This paper describes the properties and the engineering applications of the smart materials, especially in the mechatronics field. Even though there are several smart materials which all are very interesting from the research perspective, we decide to focus the work on just three of them. The adopted criterion privileges the most promising technologies in terms of commercial applications available on the market, namely: magnetorheological fluids, shape memory alloys and piezoelectric materials. Many semi-active devices such as dampers or brakes or clutches, based on magnetorheological fluids are commercially available; in addition, we can trace several applications of piezo actuators and shape memory-based devices, especially in the field of micro actuations. The work describes the physics behind these three materials and it gives some basic equations to dimension a system based on one of these technologies. The work helps the designer in a first feasibility study for the applications of one of these smart materials inside an industrial context. Moreover, the paper shows a complete survey of the applications of magnetorheological fluids, piezoelectric devices and shape memory alloys that have hit the market, considering industrial, biomedical, civil and automotive field.
Although many new materials are developed in laboratories, most of them do not get commercialized. The ranking of applications gives material engineers a better understanding of the advantages and disadvantages of any new or improved material under development. This is possible through simultaneously considering different technical, economic, and environmental criteria. It also helps to guide future research on developing new materials and identify the requirements that any new material must fulfill for the most fitting applications. The appropriateness of the proposed approach for evaluating promising applications of a new material is demonstrated using a case study in nanostructured Al/Al2O3 metal matrix composite produced via the accumulative roll bonding process. Al/Al2O3 metal matrix composite provides superior mechanical and physical properties and accumulative roll bonding is a severe plastic deformation process that can be applied to the continuous production of bulky sheet materials. The material is in growing use and becoming indispensable in several key industrial sectors such as aerospace, automobile, marine, and defense, and the enhanced properties created by accumulative roll bonding will only increase its potential. The innovative approach described in this paper will be of interest to academic researchers and practitioners involved in new materials, processing, and product development.
To improve the microstructure density of high-velocity arc spraying coating and enhance its adhesive strength and wear resistance, a plasma remelting investigation of the FeNiCrAl sprayed coating was carried out in this study. The microstructure and phase composition of the sprayed coating and the remelted coating were compared by using metalloscope, scanning electron microscope and X-ray diffractometer. The microhardness distribution and friction wear characteristics of the plasma remelted FeNiCrAl sprayed coating were investigated by microhardness tester and CETR sliding friction wear testing machine. The results showed that the remelted coating has more compact microstructure and presents metallurgical bonding with the substrate. The generation of hard phases such as (Fe,Cr)7C3 and Cr23C6 as well as solid solution (Fe,Cr) increases the microhardness of the remelted coating significantly, about 1.4 times higher than that of the sprayed coating. According to sliding friction wear test, the abrasion losses of the sprayed coating under 10 N and 20 N loads are 4.6 and 10.5 times higher than those of the remelted coating, indicating the better wear resistance of the remelted coating.
A three-dimensional finite element model for scarf-repaired composite laminate was established on continuum damage model to predict the load capacity under tensile loading. The mixed-mode cohesive zone model was adopted to the debonding behavior analysis of adhesive. Damage condition and failure of laminates and adhesive were subsequently addressed. A three-dimensional bilinear constitutive model was developed for composite materials based on damage mechanics and applied to damage evolution and loading capacity analyses by quantifying damage level through damage state variables. The numerical analyses were implemented with ABAQUS finite element analysis by coding the constitutive model into material subroutine VUMAT. Good agreement between the numerical and experimental results shows the accuracy and adaptability of the model.
Despite offering very attractive advantages over traditional joining methods, one of the setbacks of adhesive bonding is its long-term strength in aggressive environments, such as environments with high moisture and extreme temperatures. With the rise of new lightweight materials and their recent use in everyday vehicles, transportation industries have been very interested in determining the long-term behavior of adhesive joints. The aim is to build durable, lighter vehicles, which consume less energy and emit less pollution. The two main factors that affect the strength of vehicle adhesive joints are exposure to moist environments and high and low temperatures. There are some works concerning the effect of these two factors separately and some predictive models have been developed, which help the engineer to design reliable, safe, and efficient adhesive joints. However, the combined effect of temperature and moisture is not yet totally understood. This paper presents a review on the temperature and moisture degradation of adhesive joints.
Axially compressed buckled beams have been used for several decades as elastic suspensions characterized by high static stiffness and low dynamic stiffness. The most comprehensive mathematical modelling of buckled beams is based on the elastica theory, a rational framework that seeks the equilibrium configuration for arbitrarily large deflections and rotations. The use of the elastica model is straightforward for analysis purposes but is rather awkward for design tasks because it requires handling of elliptic functions. This paper presents approximate equations developed from the elastica solution to facilitate the structural synthesis of buckled-beam suspensions starting from high-level engineering specifications. The step-by-step design procedure is illustrated by means of a case study and the theoretical predictions are validated against test data and finite element results.
In the present research, vibration and instability of orthotropic graphene sheet subjected to thermo-magnetic fields are investigated. Orthotropic visco-Pasternak foundation is considered to analyze the influences of orthotropy angle, damping coefficient, normal and shear modulus. New first-order shear deformation theory is utilized due to accuracy of its polynomial functions compared to other theories of plate. Motion equations are obtained by means of Hamilton’s principle and then solved analytically. Influences of various parameters such as small scale, magnetic field, orthotropic viscoelastic surrounding medium, thickness and aspect ratio of single layer graphene sheet on the vibration characteristics of nanoplate are discussed in detail. The results indicate that the stability of single layer graphene sheet is strongly dependent on applied magnetic field. Therefore, the mechanical behavior of single layer graphene sheet can be improved by applying magnetic field. The results of this investigation can be used in design and manufacturing of micro/nano mechanical systems.
Mechatronic agricultural machines and equipment are continuously increasing their complexity and cost. In order to ensure their efficiency and reliability and preserve their value, it is important to actively monitor the working loads and register damaging and wear occurring on critical components. This approach needs the introduction of sensors on the machine, which allow continuous monitoring and evaluate the residual life of components. The work presents the development and testing of an innovative low-cost systems for monitoring and diagnostic of off-highway vehicles. The sensor measures the torque of a mechanical power transmissions, and it was designed especially for agricultural machinery. The torque transducer monitors the mechanical power flowing from the tractor into the gearbox and the agricultural implement and is fully integrated with the power take-off driveshaft, thus being generally applicable. The design and development of the transducer was performed following a quality function deployment approach. The system is less expensive considering the typical torque measuring system commercially available and, thanks to its wireless module and integrated power supply, it is reliable and generally applicable to many power take-off to implement combinations.
In this work, a characterization of a NiTiCu (Ti44.6Ni5Cu (at.%)) shape memory alloy (tube specimens) has been done via tension, compression and torsion tests conditions. Torsion tests were done in a special homemade equipment, which is based on an instrumented dividing head with a specifically designed thermal chamber. This configuration is able to measure torque and twist angle with isothermal tests at different temperatures as well as to apply thermal cycles with a fixed twist angle. Moreover, tube specimens were instrumented with stacked strain gauges rosettes in order to obtain the strain tensor. Strain gauges were also used to calibrate the equipment and to identify the real stress state in torsion tests. The results have shown differences between the shear modulus measured on torsion tests and the shear modulus calculated from the measurements at tension and compression tests due to the tension/compression asymmetry and a non-constant strain ratio value. Thermal cycling tests at different values of fixed twist angles not only have led to characterize the evolution of torque as a function of the temperature but also to understand the different interacting mechanisms in torsion tests.
Geopolymers exhibit various unique properties and characteristics, including high compressive strength, high temperature stability, and low thermal conductivity. As a relatively new and perspective material, the behavior of geopolymers subjected to high temperatures is being intensively studied nowadays. This review summarizes the recent achievements in the development of geopolymer-based fire resistance materials. Technological parameters, which influence thermal behavior of geopolymer-based materials, are also discussed. Besides that, recent applications of geopolymers according to their composition are presented.
This article describes an investigation of Veerman’s interpolation method and its applicability for determining sheet metal formability. The theoretical foundation is established and its mathematical assumptions are clarified. An exact Lagrangian interpolation scheme is also established for comparison. Bulge testing and tensile testing of aluminium sheets containing electro-chemically etched circle grids are performed to experimentally determine the forming limit of the sheet material. The forming limit is determined using (a) Veerman’s interpolation method, (b) exact Lagrangian interpolation and (c) FE-simulations. A comparison of the determined forming limits yields insignificant differences in the limit strain obtained with Veerman’s method or exact Lagrangian interpolation for the two sheet metal forming processes investigated. The agreement with the FE-simulations is reasonable.
Magnetorheological fluids are smart materials responsive to magnetic field, widely applied in dampers and shock absorbers but also in clutches and brakes. The magnetorheological fluid gap shape is a very important topic in the design of clutches, since it directly influences the transmissible torque and the power loss. In this paper, an approach to magnetorheological fluid clutch design based on optimization is proposed and tested on four different layouts. Starting from a given available volume, two magnetorheological fluid gap shapes, namely single cylinder and multi-disc, and two coils positions, i.e. internal or external, were considered. A lumped parameter model was developed to analytically compute the magnetic flux along the clutch magnetic circuit and to calculate the transmissible torque of the clutch. The optimal geometry of the clutch for maximum transmissible torque, in terms of number and dimensions of the coil sectors, was determined for each shape and coil configuration and the results were validated by finite element models.
A critical distance based method was proposed for predicting the strength of adhesive single lap joints. Using this method, the failure of SLJs was predicted when the longitudinal strain along the adhesive mid-plane reached a critical value at a specific critical distance. The two parameters of the method including the critical longitudinal strain and the critical distance can be determined using experimental results. Several single lap joints with different overlap lengths and substrate thicknesses were manufactured and tested under quasi-static loading. It was found that the critical distance was independent of the overlap length and the substrate thickness while the critical longitudinal strain was found to be dependent on the substrate thickness. However, the effect of substrate thickness on the critical longitudinal strain decreased by increasing the substrate thickness. The correlation between the experimental and predicted failure loads was found to be very well.
The tire and vehicle setup definition, able to optimise grip performance and thermal working conditions, can make the real difference as for motorsport racing teams, used to deal with relevant wear and degradation phenomena, as for tire makers, requesting for design solutions aimed to obtain enduring and stable tread characteristics, as finally for the development of safety systems, conceived in order to maximise road friction, both for worn and unworn tires. The activity discussed in the paper deals with the analysis of the effects that tire wear induces in vehicle performance, in particular as concerns the consequences that tread removal has on thermal and frictional tire behaviour. The physical modelling of complex tire–road interaction phenomena and the employment of specific simulation tools developed by the Vehicle Dynamics UniNa research group allow to predict the tire temperature local distribution by means of TRT model and the adhesive and hysteretic components of friction, thanks to GrETA model. The cooperation between the cited instruments enables the user to study the modifications that a reduced tread thickness, and consequently a decreased SEL (Strain Energy Loss) and dissipative tread volume, cause on the overall vehicle dynamic performance.
This work presents a study regarding the influence of the cooling process, as a result of different mould insert materials, on ceramic parts dimensions obtained by low-pressure injection moulding process. Discs of ceramic with Ø80 x 2 mm, composed by 86 wt.% alumina (Al2O3) and 14 wt.% organic vehicle, were produced. An experimental injection mould was designed and manufactured with built-in heating and cooling systems, controlled by a DAQ (Measurement Computing – USB-TC) and thermocouples K type. Four types of insert materials were used: aluminium alloy (AA7075-T6), electrolytic copper, brass alloy (C36000) and SAE1045 steel. Tests were carried out considering injection moulding parameters constant, i.e. initial mould temperature, injection pressure and time and extraction temperature. All the post-process (debinding by wicking; final debinding and sintering) parameters were also kept constant. Parts were analysed considering dimensions, mass, geometry, visual aspects and defects. The results showed that the cooling rate resulting from the thermal conductivity of each material has influenced more significantly the dimensional shrinkage and mass reduction of the samples during the intermediate post-processes phases. The geometric deviations were different for each condition throughout the process and they increased in the final parts. The parts produced with higher cooling rate had higher geometric deviations.
In this work, a unit cell-based micromechanical model with a proper representative volume element is proposed to evaluate the coefficients of thermal expansion of carbon nanotube-reinforced polyimide nanocomposites. The model takes an interphase between carbon nanotube and polyimide matrix into account which characterizes the non-bonded van der Waals interaction between two phases. The effects of some important parameters on the coefficients of thermal expansion such as thickness and adhesion exponent of interphase, temperature deviation as well as volume fraction, diameter and waviness of carbon nanotubes are investigated in detail. It is found that the interphase plays a critical role in determining the coefficients of thermal expansion and should be incorporated into the modeling of nanocomposite. According to the obtained results, there exists a specific value for carbon nanotube diameter beyond which further increasing in carbon nanotube diameter does not affect the coefficients of thermal expansion of nanocomposite. Also, the results reveal that the carbon nanotube waviness has a significant influence on the coefficients of thermal expansion of the nanocomposite. The results of the present model are compared with those of finite element method and a very good agreement is pointed out.
Fusion bonding is an innovative joining technology which enables connecting load-adapted material combinations, such as metals with thermoplastic polymers or fibre-reinforced polymers. The bonding process is facilitated by inductively or conductively heating the metallic joining partner and pressing it onto the plastic joining partner. Due to heat conduction, the plastic melts and wets the metallic joining partner, so that after a holding and cooling phase a bonding results without applying additional joining technologies. The connection quality and bonding strength are linked to the selected process parameters and to achieve the desired outcome, it is crucial to choose the appropriate bonding process parameters. The experimental determination of such is an intricate and complex procedure in terms of costs and time efficiency, and hence simulations have become the preferred method for the dimensioning of joints. This paper discusses the numerical illustration of the fusion bonding process between a metal and a pure plastic hybrid joint. The temperature distribution in the joining partners is a significant process parameter that affects the connection quality and bonding strength. Simulations already exist that can predict such temperature distributions.4,5 This paper builds upon a fully coupled thermal-stress analysis of the fusion bonding process and examines a possible numerical illustration of temperature distribution and mechanical displacements to make predictions about the geometric quality of the joints. For this purpose, the paper sets out to characterize the material behaviour of the polymer and hence generates material core values for the implemented material model in the simulation. The primary focus in this paper is on the temperature and shear rate-dependent viscoelastic behaviour of the plastic throughout the entire joining process temperature range. For the validation of the simulation, a real experiment has been carried out under ideal conditions.
The innovation in the railway industry is focused on the production of lightweight vehicles with high performance, in order to obtain an energy power saving and to satisfy the environmental and global community requests. To pursue this aim, new materials have been increasingly used for vehicle structures. The selection of innovative materials and the definition of the relative properties represent, however, one of the most critical aspects for the design. Several factors, such as technical requirements, strength- and stiffness-to-weight ratios, crash resistance, and cost, are involved in material selection for rail vehicles. In addition, materials have to be chosen in accordance with the reference standards concerning fire resistance. This paper describes the activity carried out in order to acquire the needed information about selected composite materials to be used in the design and validation phases for a structural rail vehicle end and a roof. The material under investigation has been manufactured in order to satisfy the strict railway light metro fire normative. Due to the novelty of the adopted composite materials, a full mechanical characterization of the lamina was needed. The orthotropic material properties were verified and tuned using further tests on laminate and sandwich configurations in order to take into account, also, the influence of manufacturing process parameters. Analytical and numerical approaches have been used to validate and optimize the structural layout. Results of the multistep material characterization, acquired during the above phases, have been used to perform computational analysis in order to further improve the component design.
Lightweight metallic lattices in the form of honeycombs are long known to exhibit a good mechanical strength/weight relation, given their geometry and relative density, in comparison with bulk materials. Due to the current developments in additive manufacturing techniques, the production of honeycombs by investment casting is now easier and may be a competitive route when compared to welding and gluing of sheet metal. This study explores the importance of the manufacturing design when producing honeycombs by investment casting. It is shown by numerical simulation and experimental procedures that mold filling in directions where horizontal ribs are present may induce defects such as interdendritic porosities. These defects have a relevant role in the elastic domain of the lattices, decreasing the apparent Young’s modulus and the plastic collapse stress. In terms of energy absorption, it is shown that these porosities have no significant effect due to the fragile fracture of both casting directions.
Dimensionally stable material design is an important issue for space structures such as space laser communication systems, telescopes, and satellites. Suitably designed composite materials for this purpose can meet the functional and structural requirements. In this paper, it is aimed to design the dimensionally stable laminated composites by using efficient global optimization method. For this purpose, the composite plate optimization problems have been solved for high stiffness and low coefficients of thermal and moisture expansion. Some of the results based on efficient global optimization solution have been verified by genetic algorithm, simulated annealing, and generalized pattern search solutions from the previous studies. The proposed optimization algorithm is also validated experimentally. After completing the design and optimization process, failure analysis of the optimized composites has been performed based on Tsai–Hill, Tsai–Wu, Hoffman, and Hashin–Rotem criteria.
The automobile industry is presently focusing on processing of advanced steels with superior strength–ductility combination and lesser weight as compared to conventional high-strength steels. Advanced high-strength steels are a new class of materials to meet the need of high specific strength while maintaining the high formability required for processing, and that too at reasonably low cost. First and second generation of advanced high-strength steels suffered from some limitations. First generation had high strength but low formability while second generation possessed both strength and ductility but was not cost effective. Amongst the different types of advanced high-strength steels grades, dual-phase steels, transformation-induced plasticity steels, and complex phase steels are considered as very good options for being extended into third generation advanced high-strength steels. The present review presents the various processing routes for these grades developed and discussed by different authors. A novel processing route known as quenching and partitioning route is also discussed. The review also discusses the resulting microstructures and mechanical properties achieved under various processing conditions. Finally, the key findings with regards to further research required for the processing of advanced high-strength steels of third generation have been discussed.
Coating of hydroxyapatite using the pulsed laser deposition technique, on medical grade UNS S31254 stainless steel (254SS), to yield a biomaterial for potential orthopedic implant applications, is unreported so far in the literature. In this paper, the pulsed laser deposition process was used to improve the physiological response of 254SS. The surface morphology of the deposited hydroxyapatite coatings was characterized using scanning electron microscopy and atomic force microscopy, while the phase composition of the deposited hydroxyapatite coatings was determined using the X-ray diffraction method. The thickness and adhesive strength of the hydroxyapatite coatings were determined using an ellipsometer and a tensometer, respectively. The antibacterial efficacy of the deposited hydroxyapatite coatings was confirmed using the modern technique of fluorescence-activated cell sorting. Finally, the bioactivity of hydroxyapatite coatings was investigated by conducting immersion test in simulated body fluid environment. The scanning electron microscopy and atomic force microscopy results revealed higher (~8 nm) average surface roughness, which is likely to facilitate better osseointegration. X-ray diffraction analysis confirmed that postdeposition annealing is essential to achieve the desired crystallinity and uniformity of coatings. Tensile pull-out tests confirmed adhesive strength of hydroxyapatite coatings beyond the standard expected values. Immersion tests inferred high bioactivity of pulsed laser deposition hydroxyapatite coatings. The promising results obtained in this research signify the potential application of hydroxyapatite coatings in orthopedic implants.
This paper presents a combined numerical–analytical approach to consider the effects of shot-peening surface treatment on the fatigue performance of metallic parts. This approach has the advantage to take into account both the favorable and unfavorable shot-peening effects. It is constituted by three principle steps: (i) a 3D finite element active simulation of the shot-peening process; (ii) prediction of the change of the shot-peened surface properties during the applied cyclic loading; and (iii) prediction of the change of the fatigue performances for both limited and high number of cycles. An application has been carried out on the aeronautical-based nickel super-alloy material, Waspaloy. The obtained results are in good correlation with available experimental investigations results and physically consistent. This proposed approach can be used to determine the optimum shot-peening conditions.
This study presents a low-cost and environmentally friendly medium for the pack boriding (boronizing) of a Ti6Al4V alloy. Titanium and its alloys are known to be highly reactive and to have extreme oxygen affinity. Therefore, boriding is performed under vacuum or in protective atmospheric conditions. This work evaluated the pack boriding heat treatments of a Ti6Al4V alloy under atmospheric conditions via the various boriding media used by previous researchers. In addition, a new pack boriding medium was developed by adding aluminum. Consequently, this study demonstrated that it is possible to obtain an undamaged titanium surface by applying solid-state boriding under atmospheric conditions.
Nowadays, natural fibre-reinforced composites find applications in almost all engineering fields. This work is an attempt to realise improvement in dynamic characteristics of micro lathe bed using Himalayan nettle (Girardinia heterophylla) polyester (NP) composite as an alternate material. In order to study and validate the improvements envisaged, a cast iron micro lathe bed is considered as reference. Numerical (FE) model of the cast iron micro lathe bed was developed and validated through experimental static and modal analysis. Finite element analysis of the micro lathe bed with the existing cast iron material as well as with nettle–polyester composite as alternate material was also carried out using worst case cutting forces, and based on the relative performances, the need for form design modification for the proposed material was identified. To enhance the bending and torsional stiffness of the nettle–polyester composite lathe bed, various cross sections and rib configurations were studied and the best among them was identified and the same was implemented in the nettle–polyester composite micro lathe bed design. Finite element analysis of the newly designed nettle–polyester composite micro lathe bed was performed and the improvements in dynamic characteristics were evaluated. The newly designed nettle–polyester composite micro lathe bed was fabricated and the predicted enhancement in static and dynamic characteristics was verified experimentally. The studies indicated that nettle–polyester composite could be considered as a suitable alternate to cast iron structures in machine tools.
The availability of additive manufacturing technologies in particular the selective laser sintering process has enabled the fabrication of high strength, lightweight and complex cellular lattice structures. In this study, the effective mechanical properties of selective laser sintering produced periodic lattice structures were investigated. Three different types of lattice structures were designed by repeating three types of open-form unit cells consisting of triangular prism, square prism and hexagonal prism. A novel approach of creating the complex and conformable lattice structures using traditional modelling software such as Creo® proposed by the authors was used. Based on the predesigned lattice structures, finite element analysis was carried out to evaluate the mechanical properties of these structures. For the experimental study, nylon samples were printed using a plastic selective laser sintering system and tested using a universal testing machine. Finite element analysis results show that lattice structures with triangular prism perform better than the other two prisms in terms of Young’s modulus to relative density ratio. Tensile tests results show good conformance with the results obtained from finite element analysis.
The characteristic highly non-linear biomechanics of soft tissues within their physiological range often involve degradation of the material properties. Some evidence shows that the stretch patterns induced in this (bio)structures lead to pathological conditions associated with the continuous degradation of the collagen fibres and ground substance of the material. In this work, a computational framework for modeling local anisotropic damage within non-linear geometrical considerations is proposed. Due to tissue and subject variability observed in the mechanical characterization of these types of materials, we adopt a strongly objective approach able to compute the material response for any functional form of the hyperelastic constitutive equations. The numerical examples of three-dimensional displacement and force-driven boundary value problems describe the capability to use multiple material models within the same computational framework. Particularities in the behaviour of the considered material models and the implications of considering damage effects to represent the Mullins effect are discussed.
Drop hammer impact experiments have been carried out to assess the dynamic plastic response of fully clamped circular and rectangular plates made of aluminum and steel subjected to hydrodynamic impact loading at various energy levels. Also, the effective parameters in forming process are proposed in non-dimensional forms for modeling and prediction of the central deflection of plates using adaptive neuro-fuzzy inference system in conjunction with genetic algorithm and singular value decomposition method. Genetic algorithm is used for optimal scheme of Gaussian membership function’s variables and multi-objective Pareto optimal design of adaptive neuro-fuzzy inference system model. Also, the singular value decomposition method is applied to compute the linear parameters of the adaptive neuro-fuzzy inference system method. The important conflicting objectives of developed adaptive neuro-fuzzy inference system, namely, training error and prediction error, are obtained by dividing date sets into two parts. Hence, various optimal choices of adaptive neuro-fuzzy inference system model are provided which are non-dominated states from each other. Moreover, optimal Pareto front of such model leads to trade-off between the conflicting pair of considered objectives for two series of experiments. The results of this work indicate that multi-objective Pareto optimal design of adaptive neuro-fuzzy inference system predicts central deflection of plates with a good accuracy. In addition, the comparison between the adaptive neuro-fuzzy inference system model and exiting one demonstrates superior performance of the present approach in simulating central deflection of plates.
This investigation essentially highlights development of novel high-performance fire-resistant polymeric nanocomposite with respect to its orientation towards future generation aviation. Therefore, an attempt has been made to increase thermal stability and fire resistivity of phenolic/cotton fabric reinforced polymer composite, which is desirable for aircraft interiors. There is considerable increase in adhesion characteristics of phenolic fabric reinforced polymer composite due to atmospheric pressure plasma treatment. The phenolic fabric reinforced polymer is subsequently coated with nanosized calcium silicate reinforced polybenzimidazole composite in order to increase thermal stability and fire resistance property. Thermogravimetric analysis reveals that polybenzimidazole-coated fabric reinforced polymer shows significantly better thermal stability than the uncoated phenolic fabric reinforced polymer. There is a significant increase in the limiting oxygen index characteristics of polybenzimidazole-coated fabric reinforced polymer when compared to the uncoated phenolic composite resulting in considerable improvement in fire resistivity of the polymers.
The purpose of this investigation is to test the laser cladding of different alloy powders onto 1045 medium-carbon steel substrates for parts remanufacturing. The types of alloy powder, laser output powers, and scanning speeds are selected as influencing factors to conduct laser cladding experiments with orthogonal design on the carbon steel 1045 substrate. Bonding shear strength and microhardness of the cladding layer and the substrate are tested and analyzed. The high resolution scanning electron microscopy and energy dispersive X-ray spectroscopy are also used to analyze cladding layers, microstructures, and elements. The experimental results show that a good metallurgical bond is formed between the cladding layer and the substrate without porous cracks and other defects. Shear stress intensity of nickel-based powder is two to three times higher than that of substrate material, while iron-based powder is five times higher than the substrate material. The type of the powder is the most significant factor and laser power is the least. The hardness of outer cladding layer is higher than that of bonding section and inner section. In the heat-affected zone, hardness is higher than that of the substrate material.
Proposing a comprehensive model to predict the fatigue life of composite structures under dynamic loading has always been a challenging problem. In this study, an attempt has been made to develop a polynomial model by utilization of experimental data together with singular value decomposition technique to estimate the fatigue life of composite materials. The model is based on a nonlinear mathematical function with effective parameters related to fatigue phenomenon in a nondimensional form. For this, four effective parameters such as cyclic stress amplitude, static strength, stress ratio, and fiber angle have been considered in modeling process. To evaluate the capability of this model a comparison has been made with some available experimental results where a good agreement is achieved. So, the obtained results demonstrate that despite system complexity and inability to extract an analytical model for estimating the fatigue life of composite materials, singular value decomposition method could be known as a useful and powerful tool for modeling.
BLOODHOUND SSC is a World Land Speed Record Vehicle designed to travel at speeds of up to 1050 mph (469 m·s–1), with the lower chassis and suspension extremely close to the ground. The shockwave from the nose of the car is expected to fluidise the desert surface of the track in Hakskeen Pan, South Africa. Sacrificial materials must be added to the exterior of the car to limit erosive wear. An open loop gas blast erosion rig was used to test materials at velocities predicted by computational fluid dynamics in the front wheel arches, an area highlighted by the BLOODHOUND SSC engineers as requiring extensive protection. Tests of potential erosion protection materials were performed at 15° and 90° Impact angle using alumina as a substitute for Hakskeen Pan soil. Testing resulted in the use of a 2-mm thick Kevlar 49 laminate and 1.2 mm thick titanium Ti 15 V-3Cr-3Sn-3Al sheet for the wheel arch liner, with titanium Ti 6Al-4V used for the wheel arch lip. The erodent mass flow rate for the application was an unknown variable during testing; the test rig used a specific erodent mass flow rate of approximately 300 kg·m–2·s–1. Depending on in-service erosion rates, the titanium liner may be replaced with either a more durable liner made from Stellite 6B or a less dense liner made from aluminium Al 6082-T6.
In our recent work, a side-vent-channel blast-mitigation concept/solution for light tactical vehicles was proposed. As a part of this solution, side-vent channels are attached to the V-shaped vehicle underbody, in order to promote venting of the soil ejecta and gaseous detonation products and, in turn, generate a downward thrust on the targeted light tactical vehicle. As a consequence, the blast loads resulting from a shallow-buried mine detonated underneath a light tactical vehicle are mitigated, improving the probability for vehicle survival. The concept was motivated by the principles of operation of the so-called "pulse detonation" rocket engines. To quantify the utility and blast-mitigation capacity of this concept, use was made of several computational and design optimization methods and tools in our prior work. It was found that the capacity of the proposed blast-mitigation solution is relatively small, but still noteworthy. The present work focuses on further improvements in the blast-mitigation capacity of the side-vent-channel solution. Specifically, the benefits offered by substitution of the all-steel side-vent channels with side-vent channels made of sandwich structures (consisting of steel face-sheets and aluminum foam core) for all-steel side-vent channels are explored. The results obtained clearly demonstrated that this substitution can improve the blast-mitigation efficiency of the side-vent-channel solution. In addition, through the use of a design optimization analysis, it was established that this improvement can be further increased through proper grading of the aluminum foam density profile through the sandwich structure core.
The creep response of a highly oriented polypropylene tape used for the manufacture of self-reinforced polypropylene or all-polypropylene composites was studied over a range of stresses and temperatures. Similar to oriented polyethylene, the creep compliance is linear viscoelastic at short loading times, whereas pronounced stress dependence is observed at longer loading times. A mathematical model is proposed, where the total deformation of the fibre is regarded as being composed of a stress-linear delayed elastic component and a nonlinear plastic flow contribution. Model predictions are in good agreement with the experimental data.
In the present work, dry sliding wear behaviour of hybrid aluminum metal matrix composites is carried out. A mixture of silicon carbide and boron carbide is used in equal fraction as reinforcement with base material AA6082-T6 to prepare AA6082-T6/SiC/B4C hybrid metal matrix composites using stir casting technique. The weight percentage of silicon carbide and boron carbide mixture taken to prepare hybrid composites is 5, 10, 15 and 20. The wear behaviour of Al-SiC-B4C composites is investigated using a pin-on-disc apparatus at room temperature, and optimization of process parameters is done using response surface methodology. The weight percentage of reinforcement, sliding speed, load and sliding distance are selected as process parameters with five levels of each. Analysis of variance shows that wear increases with increase of load or sliding distance and decreases with an increase in reinforcement or sliding speed. The experimental results revealed that the wear of Al-SiC-B4C hybrid composites has been influenced most by the sliding distance and least by weight percentage of reinforcement. The interaction between load–sliding speed is the only significant two-factor interaction in the present model which increases wear rate in fabricated hybrid composites. Further, the experimental results obtained are verified by conducting confirmation tests, and the errors found are within 3 to 7%.
The utilization of natural fiber-reinforced polymer composites is rapidly increasing in many industrial applications and fundamental research. In this work, short banana-jute fiber-reinforced epoxy-based hybrid composite was prepared by varying the fiber loading (0–40 wt.%) and different weight ratios of banana and jute fiber (1:1, 1:3, and 3:1). The physical and thermal properties such as density, water absorption, thermal conductivity, specific heat and thermal diffusivity were evaluated as per ASTM standards. A new micromechanical model was developed for evaluating the effective thermal conductivity of short fiber-reinforced hybrid composites by using the law of minimal thermal resistance and equal law of specific equivalent thermal conductivity. The thermal conductivity was calculated numerically by using the steady state heat transfer simulations. The proposed model and numerical results were validated with the experimental results and analytical methods existing in the literature. The effective thermal conductivity was predicted with the proposed model, and the finite element method is in good agreement with the experimental values and observed an acceptable range of 0–6.5% and 0–11% error, respectively. The results reveal that the composite made with banana and jute in the weight ratio of 1:3 shows minimum void content, water absorption, thermal conductivity, and thermal diffusivity at all fiber loadings. The fabricated hybrid composites were suitable for building components and automobiles in order to reduce the energy consumption.
Excellent and superior properties of alumina ceramic make it a one of the highly demanded advanced ceramics in the present competitive scenario of manufacturing and industrial applications. However, its effective and economic processing is still a challenge. The present article has targeted to experimentally investigate the influence of several process variables, namely spindle speed, feed rate, coolant pressure, and ultrasonic power on different machining performances, i.e. surface roughness, and chipping thickness. Response surface methodology has been employed to design the experiments. Microstructure of the machined samples has been evaluated and analyzed through scanning electron microscope. This analysis has revealed and confirmed the presence of plastic deformation of work surface that caused the material removal along with the dominated brittle fracture in the processing of alumina ceramic with rotary ultrasonic machining. The multi-response optimization of machining responses has been done by using desirability approach. At the optimized parametric setting, the obtained experimental values for surface roughness and chipping thickness are found to be 0.215 µm and 0.159 mm, respectively.
In the present work, short glass fiber-reinforced polyester-based hybrid composites are fabricated by the incorporation of Al2O3 particulates with three different weight percentages (0 wt.%, 10 wt.% and 20 wt.%) to evaluate their physical, mechanical, and thermo-mechanical behavior. A theoretical model has been developed for erosive wear conditions and results are compared with the experimental outcomes in order to validate the model. The mechanical properties are simulated using an explicit FE code software ANSYS. In this work, erosion test is conducted by using popular evolutionary Taguchi’s (L27) orthogonal array design to optimize the experimental results. It is observed from the analysis that the peak erosion rate occurs at 75° impingement angle for Al2O3-filled composites, whereas for unfilled composites, it occurs at 60° impingement angle. The thermo-mechanical characteristics such as storage modulus (E'), loss modulus (E''), and damping properties (Tan ) are investigated in the temperature range of 25–200 ℃. It is observed that the slope corresponding to the temperature-dependent decay of the storage modulus for 10 wt.% and 20 wt.%, Al2O3-filled composite is much higher as compared to 0 wt.% Al2O3-filled composite in the temperature range of 25–75 ℃. However, the storage modulus for 10 wt.% and 20 wt.% Al2O3-filled composites remain almost same in the range of 25–60 ℃. Finally, the surface morphology of the eroded composites is examined by using scanning electron microscope and the possible wear mechanisms are discussed.
As the mechanism by which material is lost from ductile surfaces during solid particle erosion is still a matter of scientific debate, the work presented in this paper is aimed at trying to shed more light on the mechanism by which material is detached from ductile surfaces during solid particle erosion. Moreover, validating some of the most widely accepted models that predict erosive wear rate will form part of the paper. A specially designed test rig was used to facilitate test condition of an extensive experimental program. Results of the test program showed that plastic strain accumulation is largely responsible for material loss from ductile surfaces, even at cute impact angles. The key to this finding is the drop of erosive wear upon impact angle reversal indicates. It has been shown that none of the most widely accepted models of erosive wear could explain the result obtained under condition of impact angle reversal.
The objective of this research is to study the strain forming limits of Al–Mg alloy (5083) sheet, fabricated by equal channel angular rolling process at room temperature. For this purpose, the equal channel angular rolling process was executed at room temperature in three passes. Mechanical properties, microhardness, and microstructure were investigated after the equal channel angular rolling process. Uniaxial tensile tests of the equal channel angular rolling process produced samples and showed that yield and ultimate stresses increase, while the uniform elongation to fracture decreases in comparison with the annealed state. There was a continuous hardness enhancement by increasing the number of the equal channel angular rolling passes. After the third pass, the amount of hardness raised by 73% in comparison with the annealed sample. In the fourth pass, the hardness reduced slightly, that was attributed to the strain saturation in room temperature and was followed by high surface cracks. In the annealed condition, the average grain size was 45 µm, and after the third equal channel angular rolling pass, this amount was reduced to 10 µm. Furthermore, the forming limit diagrams were determined experimentally, using the Nakazima test. The obtained results show that after the third pass, the forming limit diagrams’ level move downward, meaning that a reduction occurred in the forming limits of equal channel angular rolled samples.
This study introduces an empirical analysis approach to assess mechanical behavior of thin circular mild steel plates subjected to uniform and localized impulsive loading. The empirical models have been derived by singular values decomposition procedure to predict midpoint deflection of circular plates. The essence of empirical analysis is based on dimensionless numbers. For this, Jones’s dimensionless number is considered as a dimensionless number for both uniform and localized loading. This number has some features such as considering plate geometries, mechanical properties of material, and loading conditions. The well-known Cowper–Symonds constitutive equation has been used to investigate the potential influence of material strain rate sensitivity where the constant parameters in this equation are considered as a function of plate thickness. In localized impulsive loading, two other dimensionless numbers are appended to investigate the effects of changing load ratio and standoff distance. The results of empirical models are compared to the other experimental and theoretical studies which have been performed by different researchers. Also, the obtained results show that the presented models have much less root mean square error than the other ones. Hence, these models are suitable to predict midpoint deflection of thin circular plates subjected to both uniform and localized impulsive loading.
Short fibre reinforced thermoplastics are being considered for light- and medium-duty engineering applications because of their improved mechanical strength combined with cost-effective advantages. In recent years, the carbon nanotube reinforced thermoplastics are being preferred over the short fibre reinforced thermoplastics because of the absence of directional shrinkage characteristics, directional mechanical and tribological properties. In this work, 1 wt% carbon nanotube–polypropylene material was injection-moulded to spur gears and evaluated for the durability using in-house developed power absorption gear test rig. During testing, the net surface temperature of the test gears and in-line torque available at the driver and driven shafts were continuously measured. The measured torque was used to evaluate the transmission efficiency of the test-steel gear pair. The measured net surface temperature was correlated with the gear failure mode. Test gears were run up to failure or up to 8.6 x 105 cycles, whichever occurred first. Worn-out gear tooth surfaces were observed using an optical and scanning electron microscope to understand the wear mechanism. In the initial stage of service, test gears exhibited less wear near the pitch region compared to the tip and root regions. This behaviour is due to the maximum sliding velocities at the tip and root regions compared to the pitch region. The carbon nanotube–polypropylene gears exhibited lower surface temperature (5–10 ℃), improved service life (30%–80%) and higher transmission efficiency (1–1.5%) compared to the polypropylene gear.
In this study, 6 mm thick AA6061-T6 plates were friction stir welded (FSWed) at different traveling speeds while Al2O3 nano-particles were incorporated between adjoining plates. The solution heat treatment was applied on samples for one hour at 540 ℃ and subsequently aged for 18 h at 180 ℃ to investigate the effect of post-weld heat treatment on mechanical properties of specimens. All joints were investigated macro- and micro-structurally. The microstructural characterization of the FSWed samples was carried out using scanning electron microscopy (SEM) and light microscopy techniques. Distribution of Al2O3 nano-particles in the stir zone was studied by SEM. The specimen FSWed at 40 mm/min exhibited the most homogeneous particles distribution. Tensile properties including ultimate tensile strength, elongation, and fracture surfaces were studied. Microhardness of specimens was also investigated. Surprisingly, all specimens exhibited inferior hardness compared to the as-received AA6061-T6 alloy. This phenomenon was attributed to the dissolution of precipitates during FSW process.
Quartz ceramic has been well observed as one of the highly demanded advanced ceramics which is receiving enlarging industrial approbation owing to its excellent and superior properties. However, its fruitful processing with traditional and non-traditional machining methods is still a challenge. The current article has aimed to experimentally investigate the influence of several process variables, namely, spindle speed, feed rate, coolant pressure, and ultrasonic power on machining characteristics of interest, i.e. chipping size, and material removal rate in rotary ultrasonic machining of quartz ceramic. Response surface methodology has been employed to design the experiments and the variance analysis test has also been performed with a view to observe the significance of considered parameters. Microstructure of machined samples has also been evaluated and analyzed using scanning electron microscope. This analysis has revealed and confirmed the presence of dominating brittle fracture that caused removal of material along with the slighter plastic deformation in rotary ultrasonic machining of quartz ceramic. The soundness and competence of the developed mathematical model have been established with test results. The multi-response optimization of machining responses has also been done by utilizing desirability approach, and at optimized parametric setting, the obtained experimental values for material removal rate and chipping size are, 0.6437 mm3/s and 1.3326 mm, respectively, with the combined desirability index value of 0.949.
Equal channel angular rolling process is defined as a severe plastic deformation method that imposes very large plastic strain on a material in order to enhance its mechanical properties and grain structure refinement. In this study, residual stress profiles through the thickness of St12 strips that were subjected to different passes of equal channel angular rolling were investigated by slitting method. Also, the effects of different routes of equal channel angular rolling (A and C) were studied on the mechanical properties and residual stress. Furthermore, the effect of post annealing on the mechanical properties and residual stress of 4-pass equal channel angular rolled strip was examined. The results showed significant increase in the yield strength, ultimate tensile strength, and micro hardness of the samples in both routes. But the elongation decreased. Considerable magnitude of residual stress was created through the thickness of equal channel angular rolled samples such that the maximum tensile residual stress of some samples raised to about half of the corresponding yield strength. The maximum magnitude of residual stress in route C was smaller than that in route A.
This paper presents a topology optimization method to design periodic unit cell in cellular materials with extreme properties using a moving iso-surface threshold method. The aim is to determine the optimal distribution of material within the periodic unit cell. The effective properties of cellular material are obtained by using a finite element-based homogenization method. The penalty function approach is introduced to construct the objective function for designing material with extreme properties under condition of square or isotropic symmetry. New characteristic response functions of moving iso-surface threshold are proposed for maximum shear or bulk modulus, maximum shear modulus or negative Poisson’s ratio under isotropic symmetry. Several examples are presented and the results are compared to those obtained with the solid isotropic material with penalization method to demonstrate the validity of the method. A series of new and interesting microstructures with extreme properties are found and presented.
In this study, the effect of tool shoulder diameter (D) to the plate thickness (Tp) ratio on tensile and impact toughness properties of friction stir-welded naval grade high-strength low-alloy steel was investigated. A naval grade high-strength low-alloy steel of 5 mm thick plates was welded with tool rotational speed of 600 r/min and welding speed of 30 mm/min using tungsten-based alloy tools having D/Tp ratio varying from 4 to 6. Microstructural characteristics of the weld joints were analyzed using optical microscopy and scanning electron microscopy with energy dispersive spectroscopy along with the evaluation of tensile properties. From this investigation, it was found that the joint fabricated using a D/Tp ratio of 5 (25 mm shoulder diameter) exhibited superior mechanical properties compared to other joints.
Three arrangements of reinforced A356-based composites were fabricated. Samples with 3 wt% Al2O3 (average particle size: 170 µm), 3 wt% SiC (average particle size: 15 µm), and 3 wt% of mixed Al2O3–SiC powders (each reinforcement 1.5 wt%) were fabricated. The novel fabrication process of two-step stir casting followed by rolling was utilized. Analysis of the effect of using bimodal-sized ceramic particles and process parameters on the microstructure and mechanical properties of the composites was examined. Electroless deposition of nickel was used to improve the wettability of the ceramic reinforcements by the molten metal. From microstructural characterization, it was found that fine SiC particles were agglomerated, including when coated with Ni–P. It was also revealed that the rolling process broke the fine silicon platelets within the A356 matrix, which were mostly observed around the Al2O3 particles. The processed microstructure of the composite was altered in comparison to conventionally cast A356 MMC by translocation of the fractured silicon particles, by improving the distribution of fine SiC particles, and by elimination of porosities remaining after casting. A good bonding quality at matrix–ceramic interface was formed during casting and no significant improvement was found in this regard after the rolling process. The mechanical properties of the composites tested showed that the samples, which contained the bimodal ceramic particle distribution of coarse Al2O3 and fine SiC particles produced the highest levels of composite strength and hardness.
Experimental studies are presented on the high velocity impact behavior of nanomaterial dispersed resin viz laminates made using E-glass fabric with epoxy resin. The nanomaterials used are silica nanoparticles and carboxyl functionalized multi-walled carbon nanotube (COOH-MWCNT) for polymer matrix composites. The composites' ballistic limit (Vbl) and impact energy absorbed (Eab) were determined by subjecting the material to impact loading of 85, 100, and 112 m/s by conical nose projectile. It was found that the high velocity impact response of epoxy composites improved when a nanomaterial was used as reinforcement. COOH-MWCNTs reinforced composites exhibited better energy absorption than silica nanoparticles composites. Moreover, the damage pattern for different types of materials studied is presented. It is observed that the damage size on the target around the point of impact decreases on addition of nanoparticles especially COOH-MWCNTs. Quantitative data are presented for high velocity impact behavior of the seven types of specimens studied.
The present work aims at the determination of thermal buckling loads of various functionally graded material beams with both ends clamped. Thermal loading is applied by applying linear temperature distribution and nonlinear temperature distribution at steady state heat conduction condition, across the beam thickness. Temperature dependences of the material properties, considered in the formulation, make the present problem physically nonlinear. Also, the effect of limit thermal load at which the effective elastic modulus and/or thermal expansion coefficient become theoretically zero is considered. The mathematical formulation is based on Euler–Bernoulli beam theory. An energy based variational principle is employed to derive the governing equations as an eigenvalue problem. The solution of the governing equation is obtained using an iterative method. The validation of the present work is carried out with the available results in the literature and with the results generated by finite element software ANSYS. Four different functionally materials are considered, namely, stainless steel/silicon nitride, stainless steel/alumina, stainless steel/zirconia, and titanium alloy/zirconia. Comparative results are presented to show the effects of variations of volume fraction index, length–thickness ratio, and material constituents on nondimensional thermal buckling loads.
In this study, a damage model that accounts for the effect of seawater ageing is proposed. The model is based on a failure criterion that takes into account the effect of the ply thickness, while the kinetics of the damage development are based on a Finite Fracture Mechanics approach. The stiffness degradation is identified by a multiscale approach. The parameters of the model are physically based which facilitates the identification and the coupling with the ageing. These and their evolution as a function of the time of immersion in seawater have been identified for a carbon/epoxy composite. The changes in crack density as a function of the applied load for three ageing times are quite well predicted by the model. The model explains why the damage threshold is strongly influenced by the ageing while the kinetics of the crack propagation remain quasi-constant.
A newly developed Ag–9Pd–9Ga active filler was vacuum brazed, and the mechanical properties between the metallic interconnects (SS430, Crofer22 APU, Crofer22 H) and a Ni–yttria-stabilized zirconia cermet anode were systematically investigated. The results indicate that the bonding between metal and cermet is well established and that the interface is smooth. The joint strength evaluated at both 25 ℃ and 800 ℃ under shear and tensile loading conditions confirmed that the brazed Ag–9Pd–9Ga sealant compared favorably with its commercially available glass-ceramic GC-9 counterpart.
Electrochemical machining is a promising method for titanium alloy processing. The polarization characteristics of Ti6Al4V were studied in detail in order to provide a deeper understanding of this method. The polarization curve of the alloy, which shows the relationship between current density and potential under an external electric field, was obtained in NaBr electrolyte at three different concentrations in a three-electrode electrochemical test system. The surface topography of the polarization zone and pits was examined by scanning electron microscopy, and their fractal features were calculated by the picture point cover method. The results show that Ti6Al4V in the more concentrated electrolyte has higher dissolution rate, lower decomposition potential, and more uniform surface topology in the polarization areas.
The aim of the present study is to investigate the dynamic mechanical and thermal properties of hybrid jute/sisal fibre reinforced epoxy composites. The hybrid composites were prepared by hand layup technique having total fibre loading of 30% by weight with different weight ratios of jute and sisal fibres. Dynamic mechanical properties such as storage modulus (
The presented work focuses on the effects of water degradation on the long-term behaviour of adhesive joints. The objective of this study is to measure the evolution of various mechanical properties such as tensile stress and fracture toughness as a function of humidity for two distinct adhesives, using bulk adhesive and double cantilever beam specimens in unaged and aged conditions in order to understand the influence of humidity on the adhesive properties. A mathematical equation that allows the prediction of each property degradation as a function of water is proposed and validated, which takes into account various parameters such as the diffusion coefficient, resulting in a general equation for mechanical property degradation prediction of potentially any adhesive. It was also found that the distinct adhesive properties such as strength, stiffness and fracture toughness all decreased due to water degradation with the exception of the strain that increased, concluding that water reduces the joint strength and lifespan of the studied adhesives, although in different ways.
The Advanced Combat Helmet (ACH) currently in use is designed for maximum protection against ballistic impacts and hard-surface collisions. It has been well-established now that the ACH provides relatively little protection against blast, and that a significant fraction of the soldiers returning from the recent conflicts suffer from traumatic brain injury (TBI). In the present work, an augmentation of the ACH, which involves the use of a polyurea (a nano-segregated elastomeric copolymer)-based external coating for improved blast protection is considered. To test the utility of this approach, blast experiments are carried out on instrumented head-mannequins. Three configurations of the head-mannequins are investigated: (i) unprotected; (ii) protected using a standard ACH; and (iii) protected using an augmented ACH. To provide additional insight into the problem of blast-wave interaction with a head-mannequin, a series of complementary combined Eulerian/Lagrangian transient non-linear dynamics computational fluid/solid interaction finite-element analyses is carried out. The results obtained clearly demonstrated that the use of the augmented ACH affects (generally in a beneficial way) head-mannequin dynamic loading and kinematic response as quantified by the intra-cranial pressure, impulse, acceleration, and jolt.
In the present study, wave propagation characteristics of double-walled boron nitride nanotubes (DWBNNTs) conveying ferrofluid is investigated. Magnetite (Fe3O4) nanofluid is selected as a conveying fluid which reacted in presence of magnetic field. Shear effects of surrounded medium are taken into account using Pasternak model. Stress and strain–inertia gradient elasticity theories are used due to their capability to interpret size effect. Based on Hamilton’s principle and employing Euler–Bernoulli, Timoshenko and Reddy beam models, wave equations of motion in double-walled boron nitride nanotubes are derived and solved by harmonic solution. Regarding the various types of flow regimes in fluid–structure interaction, the upstream and downstream phase velocities of double-walled boron nitride nanotubes conveying ferrofluid are calculated. A detailed parametric study is conducted to clarify the influences of the beam models, size effect theories, magnetic field, surrounding elastic medium and fluid velocity on the wave propagation of double-walled boron nitride nanotubes conveying ferrofluid. The results indicated that in lower wave numbers, the effect of flowing fluid and the difference between the upstream and downstream phase velocities were considerable. The results of this work can be used in design and manufacturing of nanopipes and nanovalves conveying fluid flow to avoid water hammer phenomenon.
This study investigates the thermal stress and deformation states of bi-directional functionally graded clamped plates subjected to constant in-plane heat fluxes along two ceramic edges. The material properties of the functionally graded plates were assumed to vary with a power law along two in-plane directions not through the plate thickness direction. The spatial derivatives of thermal and mechanical properties of the material composition were considered, and the effects of the bi-directional composition variations and spatial derivative terms on the displacement, strain and stress distributions were also investigated. The heat conduction and Navier equations describing the two-dimensional thermo-elastic problem were discretized using finite-difference method, and the set of linear equations were solved using the pseudo singular value method. The compositional gradient exponents and the spatial derivatives of thermal and mechanical properties of the material composition were observed to play an important role especially on the heat transfer durations, the displacement and strain distributions, but had a minor effect on the temperature and stress distributions.
This paper presents a new combined experimental and theoretical methodology for determining the formability limits by wrinkling in sheet metal forming. The methodology is based on the utilization of rectangular test specimens clamped along its narrower sides and compressed lengthwise and is aimed at replicating the physics behind the occurrence of wrinkling in deformation regions submitted to in-plane compression along one direction. The methodology draws from a previous development in the field of flexible roll forming, and the overall objectives are to enhance and improve its methods and procedures and to provide a new level of understanding on the onset of wrinkling in sheet metal forming. Experimentation and finite element modelling of cylindrical deep-drawing without blank holder combined with the utilization of the space of effective strain vs. stress triaxiality are employed to discuss the applicability and validity of the new proposed methodology for determining the formability limits by wrinkling.
Forming limit diagram is often used as a criterion to predict necking initiation in sheet metal forming processes. In this study, the forming limit diagram was obtained through the inclusion of the Marciniak–Kaczynski model in the Nakazima out-of-plane test finite element model and also a flat model. The effect of bending on the forming limit diagram was investigated numerically and experimentally. Data required for this simulation were determined through a simple tension test in three directions. After comparing the results of the flat and Nakazima finite element models with the experimental results, the forming limit diagram computed by the Nakazima finite element model was more convenient with less than 10% at the lower level of the experimental forming limit diagram.
This paper investigates the effect of nickel particulate on mechanical behavior and sliding wear performance of novel Co30Cr4Mo alloy for orthopedic hip implant application with and without an introduction of distilled water (i.e. both dry and wet conditions) medium. The mechanical behavior is examined by the micro-hardness tester and the compression testing machine, while the wear performance is analyzed through a pin-on-disc tribometer where the samples slide against a counter disc made up of hardened alloy steel (EN-31) under different operating conditions at room temperature. Scanning electron microscope, atomic force microscopy, and X-ray diffraction are used to examine the surface morphology, worn surface profile, and cross-sectional microstructure of the fabricated alloy (Co30Cr4Mo) composite. In this study, at the beginning, steady state experimental analysis is carried out to find the volumetric wear loss and friction coefficient by varying the sliding velocity and normal load, respectively. After obtaining the steady state results, the Taguchi design of experiment has been conducted followed by statistical analysis of variance to identify the significant factor setting for obtaining better performance output. From the analysis, it is found that by increasing the nickel wt.%, the hardness and the compression strength of the fabricated alloy composites are increased. Furthermore, the fabricated alloy composite with 1 wt.% Ni shows the better wear resistance under different operating conditions in both dry and wet media. This study will give an idea for hip implant application but not direct replacement of human joints. In future, this study may be extended in more detail for biomedical applications for replacement of either human hip implant or animal implant, respectively.
A laser source is most popular in industrial world for its high cutting efficiency and productivity. In the present research work, laser cutting of aluminium metal–matrix composite has been studied. The investigations have been done to analyse the influence of various parameters on surface and quality characteristics of aluminium alloy 5052 reinforced with ZrO2 particles. The effect of laser parameters was analysed on striation angle, heat affected zone and kerf deviation. Response surface methodology has been applied using Box-Behnken design for the statistics analysis. Heat affected zone and striation formation of laser cut surface were examined using scanning electron microscope and optical microscope. The effect of arc radius, cutting speed and percentage of reinforced particles was found to be significant on all output characteristics. The predicted response surface methodology (RSM) model was validated with experimental data for determination of accuracy level.
In this work, carbon nanotube (CNT) reinforced polypropylene (PP) composites (0.5, 1.0, 3.0, and 5.0 wt%) were developed using the melt compounding process. The developed composites were injection-molded into tensile specimens and pins to evaluate the mechanical and tribological properties of the composites. As the CNT content increased, the tensile strength and Young’s modulus of the PP composites increased. The addition of the CNTs to the PP matrix beyond 1 wt% demonstrated agglomeration, and fractured tensile specimens confirmed this behavior. Developed materials demonstrated enhanced crystallinity up to 1 wt% CNT and, subsequently, decreased crystallinity beyond 1 wt% CNT, and an X-ray diffraction investigation confirmed this behavior. The measured coefficient of friction, online wear, and weight loss from the sliding wear test confirmed the least frictional resistance and maximum wear resistance for the 1 wt% CNT–PP composite. As the CNT content increased, the hardness of the CNT–PP composite increased up to 1 wt% CNT and decreased beyond this threshold. The worn-out surfaces of the CNT–PP composite observed using a scanning electron microscope and noncontact three-dimensional profiler confirmed the superior wear resistance of the 1 wt% CNT–PP composite. The CNT–PP composites considered in this study exhibited increased surface temperatures in the sliding wear condition because of the addition of the CNTs. The addition of the CNTs to the PP material increased the thermal conductivity of the composite.
Boron carbide /aluminum composites have been produced on an aluminum–silicon cast alloy using friction stir processing. Effect of pin profile on the distribution of boron carbide in the stir zone of the friction stir processed specimens was investigated experimentally and numerically. The material flow generated by the threaded and circular tool pin profiles, being the main reason for the distribution of particles in the metal matrix, was numerically modeled using a thermomechanically coupled three-dimensional finite element model. Numerical and experimental results show that threaded pin profile produces a more uniform distribution of B4Cp than other pin profiles. Hardness tests were performed in order to investigate mechanical properties of the composites. Wear resistance of the composite was evaluated and obtained results showed that the hardness and wear resistance of the composite significantly improved.
Riblets are a well-researched and understood passive method for achieving viscous drag reduction. Since the 1970s, researchers have found that, with riblets, viscous drag reduction in the order of 8% is achievable in turbulent air and fluid flows. Most of the relevant literature provides insight into the drag-reductive mechanisms of riblets and the effect of riblet morphological design in varying flow conditions. A few recent studies have begun to investigate the influence of material properties on the drag-reductive ability of riblet surfaces with promising results. We here provide an updated review of material selection and riblet manufacture and show current trends. A brief summary is provided of the theories of riblet drag-reductive ability, riblet surface design, the role of material selection for drag reduction and current manufacturing techniques.
This paper investigates the collapse by buckling of hollow polyvinylchloride profiles with various cross sections. The presentation identifies the modes of deformation and the critical buckling loads and investigates the possibility of developing innovative mechanical joining processes built upon the formation of bellow shapes (wrinkles) by radial outward flow. The methodology draws from the fundamentals of material characterization and plastic buckling by compression between flat parallel platens to the experimental and finite element analysis of the formation of wrinkles by compression in a semi-closed tool. Results show that the formation of wrinkles in hollow polyvinylchloride profiles at room temperature is limited to geometric features within a compact range. The connection of hollow polyvinylchloride profiles to polycarbonate sheets is given as examples of application of wrinkles in mechanical joining.
Characterization of yttria-stabilized zirconia coatings deposited on AA2024-T351 aluminum alloy by air plasma spraying is carried out in the present work to assess its applicability as a thermal barrier coating on automotive components aluminum alloys. Tetragonality of coating microstructures was confirmed through X-ray diffractometer, transmission electron microscopy, and high-resolution transmission electron microscopy. Lattice-image spacing obtained from high-resolution transmission electron microscopy confirmed multilayer structure of the coating and that the tetragonal phases are stable. From the optical microscopy it was found that there are good coating particle distribution and homogeneity of coating particles on the substrate while atomic force microscopy provided information about surface bumps and pits. Small roughness of the coating microstructure was found to be very low. Small roughness showed good deposition efficiency of the coating structures.
In this study, strip cyclic extrusion-compression was introduced as a modified counterpart of cyclic extrusion-compression process for producing ultrafine grained strips. The strip cyclic extrusion-compression method was applied to the pure aluminum and mechanical properties of the processed strips were investigated. The ultrafine grained strips were successfully processed by applying two cycles of strip cyclic extrusion-compression. The transmission electron microscopy observations revealed that the initial microstructure was refined to 1 µm and 650 nm after the first and second cycles, respectively. The yield strength was increased 3 times and the ultimate strength was enhanced 1.5 times after the application of two cycles. The microhardness of the processed strips was increased to 46 Hv and 58 Hv after the first and second cycles, respectively. Furthermore, the fatigue tests revealed that the fatigue strength was higher in the strip cyclic extrusion-compression processed material than the un-processed one. The microstructure evolution during strip cyclic extrusion-compression was also modeled by means of a dislocation density-based finite element method. The finite element method model predicted that the microstructure was refined to 950 nm and 690 nm after the first and second cycles, respectively.
This paper presents the numerical investigation results carried out on vibro-acoustic behavior of functionally graded carbon nanotube reinforced polymer nanocomposite plate using combined finite element method and Rayleigh integral. Parameter studies are carried out to analyze the influence of nature of functional grading, loading of carbon nanotube, and structural boundary conditions on free and forced vibration and sound radiation characteristics in detail. It is found that natural frequencies are significantly influenced by the nature of functional grading while the mode shapes are insensitive. The resonant amplitude of vibration and acoustic response are significantly influenced with the nature of different functional grading. This reflects in the bandwise calculation of sound power also which recommends the carbon nanotube functional grading with X distribution along the thickness direction for lower frequency level. Similar variation in vibro-acoustic response has been observed with increase in the carbon nanotube loading also.
This article presents the results of a study on the corrosion characteristics of the single and dual particle reinforced aluminum alloy 6063 based composites. The reinforcements of silicon carbide and zircon sand were utilized to fabricate the composites by stir casting technique. The influence of reinforcement and their weight percentage on the hardness variations was investigated. The electrochemical tests in sodium chloride solution were conducted to study the corrosion performance of reinforced composites and base alloy. From the corrosion analysis, it was observed that the single particle reinforcement offered better solution on enhancing the corrosion resistance of base aluminum alloy in comparison with dual particle reinforced composites. In the single particle reinforced composites, addition of zircon sand exhibited increased corrosion resistance, when compared to silicon carbide reinforced composites. The governing mechanism behind increased corrosion resistance was found to be the absence of galvanic coupling between the elemental compounds and the corrosive media at particle–matrix interface. The scanning electron microscopy of composites was performed to analyze corrosion mechanism and correlated well with the corrosion behavior.
Alumina coated lightweight brake rotors were investigated to evaluate the effect of coating properties on their friction performance and thermal durability. An alumina ceramic coating on AA6082 aluminium alloy (Al-Alloy) and on 6061/40SiC aluminium metal matrix composite (Al-MMC) prepared by plasma electrolytic oxidation was studied using a programme of brake dynamometer and material characterisation tests. The results showed that the plasma electrolytic oxidation alumina layer adhered well to the Al-alloy substrate and was more uniform and durable when compared to that on the aluminium metal matrix composite. The plasma electrolytic oxidation layer significantly improved the hardness of the rotor surface for both Al-alloy and aluminium metal matrix composite substrate. The coated Al-alloy disc brake rotor was demonstrated to give good thermal and friction performance up to high rubbing surface temperatures of the order of 550 ℃, but the rotor eventually failed due to temperature build-up at a critical location.
In the present work, equal channel angular pressing of commercial pure aluminum 1070 was performed up to 4 passes using route Bc. For equal channel angular pressing operation, a suitable die set was designed and manufactured. X-ray diffraction analysis was used to determine the microstructure of the equal channel angular pressing-ed material. The fracture surface morphology and microstructure after fatigue were investigated by scanning electron microscopy. Mechanical properties of the equal channel angular pressing-ed material were evaluated by hardness and tension tests. Also, cyclic deformation behavior of severe plastic deformation Al1070 has been studied and results show a significant variation in hardness, ultimate strength and fatigue properties in high cycle fatigue life. Coefficient of fatigue strength 'f and Bridgman correction factor have been obtained by S-N curve and tension test specimens, respectively, and compared before and after equal channel angular pressing process. Also an useful relation has been derived between fatigue life (Nf) and stress amplitude (a) in high cycle fatigue region. Results indicated that there was not clear relation between fatigue strength coefficient and true corrected fracture stress in this case.
In the present study, a crystal plasticity finite element model was developed for simulating the microstructure evolution and grain refinement during tube cyclic expansion-extrusion as a severe plastic deformation method for tubular materials. A new approach was proposed for extracting the real deformation history of a representative volume element during severe plastic deformation methods. The deformation history of a representative volume element during four cycles of tube cyclic expansion-extrusion was extracted by the proposed approach. Then, in a crystal plasticity finite element model, the deformation history was applied to a two-dimensional polycrystalline representative volume element with randomly assigned crystalline orientations. The intergranular interactions between grains and the intragranular orientation gradients were successfully simulated by the crystal plasticity finite element model. The distribution of misorientation angles, the evolution of grain boundaries, and the achieved average grain size after different cycles of tube cyclic expansion-extrusion were investigated by the crystal plasticity finite element model. On the other hand, ultrafine grained aluminum tubes were processed by four cycles of tube cyclic expansion-extrusion and the grain size of the processed tubes was studied by scanning electron microscopy observations and X-ray diffraction analyses. The experimental and predicted (by crystal plasticity finite element model) average grain sizes were compared.
To carry out virtual nano-indentation and nano-scratch Kevlar® 49 single-fiber tests, a multi-scale computational framework has been developed and employed. Such tests are generally conducted to determine fiber local properties, as well as to provide some insight into the interaction of hard nano-particles with the fibers. The Kevlar® fabric-based soft armor is infused with these nano-particles for improved ballistic resistance, and tip geometry of the nano-indentation/-scratch probes is selected to match nano-particle size and geometry. Due to the fact that Kevlar® 49 fibers (typical diameter 12 µm) are effectively assemblies of parallel fibrils (typical diameter 100–300 nm), while atomic bond length in Kevlar® fibers is of the order of 0.2 nm, a continuum-level finite-element framework has been developed. However, to more accurately account for some of the key aspects of the fiber-material constitutive behavior, e.g. inter-fibril cohesion, the continuum-level computational analysis has been supplemented with atomic-level molecular-statics/-dynamics calculations. In good agreement with their experimental counterparts, the results obtained revealed that the extent of participation of different fibril-deformation modes (e.g. transverse compression, inter-fibril shear, axial tension, axial tensile fracture, fibrillation, axial compression, buckling and pile-up formation ahead of the nano-scratch probe, etc.) is a function of the indentation/scratch depth. Also, a relatively good agreement was obtained between the computed and experimentally measured nano-indentation forces/energies for both shallow and deep indentations, and for the nano-scratch forces/energies, but only for shorter scratch lengths. At longer scratch lengths, the "short-fiber" effects cause the computation/experiment agreement to worsen.
The manufacturing process of bone scaffold structures has an important influence on the final mechanical strength of the structure. When the structures are not produced properly, i.e. have imperfections such as missing parts or slightly displaced joints, they lose some of their mechanical properties. The aim of this study was to see how different types of damage affect the structures and also if their effects are equal when the structure is subjected to different load conditions. The change of the mechanical behavior was determined using the commercial finite element software MSC Marc Mentat. In turn, the damage was introduced by manipulating the structure’s files (ASCII data files) using the programming language Fortran. Apart from the numerical simulations, experimental testing was also performed to verify the numerical results. In the frame of this study, useful information for further research is provided.
Resistance spot welding is one of the most commonly used processes for joining-metal the automotive, and electronics industry. When joining a car body, the method of welding dissimilar three sheets, including high strength steel is frequently used. Studies on the dissimilar welding of high strength steel and low carbon steel are being conducted in an attempt to improve the weldability. However, the dissimilar welding of TWIP steel with other steel grades is extremely challenging due to the high resistivity of the base metal. Therefore, further studies are required to improve the weldability of three sheets including the low carbon steel. In general, the resistance spot welding process is conducted in the field by the constant current control method. In this study, the constant power control method was applied in order to reduce the occurrence of expulsion and to improve the weldability of three dissimilar steel sheets consisting of SGACEN, DP steel, and TWIP steel. The constant current control was compared with constant power control, through the evaluation of weldability by using the suitable welding range lobe curve, which takes into account the tensile shear strength, and nugget diameter. Additionally, the current, voltage, resistance, and power signal were also analyzed. The constant power control prevented the occurrence of expulsion as a result of high heat not being generated at the early stage, compared to the constant current control method. Regarding the welding time being long, an increase in heat was applied so that there was a considerable improvement of weldability, compared to the constant current control.
Functionally graded materials (FGM) are newly developed materials described by variation in the characteristics gradually over volume. These materials find applications in very high temperature environments namely aerospace industry, nuclear reactors, gas turbines, and electronics cooling. These materials are used in high temperature environments with dynamic load conditions, so their transient thermoelastic analysis under these conditions is necessary. In this paper, transient thermoelastic investigation of FGM is carried out using finite element method (FEM). The effect of temperature dependence is considered in the thermophysical properties of a FGM plate in the direction of its thickness. FEM is applied to solve the thermo mechanical equations and Newmark direct integration scheme is used for obtaining the solution for transient loading. This method improves the accuracy for three dimensional cases and produces solutions directly in time domain. A comparative study is made with some existing methods, and it is found that temperature and thermal stresses remain within safe limits at higher temperatures while preserving the deformation in the structure. The results show that the grading parameter has a dominating effect on transient thermoelastic behavior on FGM plate.
This research work examined series of dental composite materials containing nano-fillers (nanoalumina, nanosilica, and nanozirconia) and micro-filler (gypsum) to determine their effect on the physical, mechanical, and wear properties. The proportions of the silanized fillers varied from 0 to 3 wt.% in an acrylate based (50 wt.% BisGMA, 49 wt.% TEGDMA, 0.2 wt.% Camphorquinone, and 0.8 wt.% ethyl 4-dimethylaminobenzoate by weight) matrix. The physical, chemical, and mechanical tests such as void content, polymerization shrinkage, water sorption, hardness, compressive strength, and flexural strength (FS) were performed. Three body abrasive wear tests were performed in a dental wear simulator machine under varying load, speed, and temperature conditions. The finding of research indicated that the dental composite filled with 3 wt.% silanized nanozirconia exhibited maximum hardness, maximum FS, and maximum wear resistance whereas, dental composite filled with 2 wt.% silanized nanoalumina filler indicated maximum compressive strength. Gray relational analysis method was applied to rank the dental composite using several performance defining attributes. These results indicated that the best combination of mechanical and wear properties were exhibited by dental composite filled with 3 wt.% silanized nanozirconia.
This paper focused on the effect of in-process cooling conditions (coolants and flow rate) on the temperature history, the tool applied forces, wear resistance, mechanical, and microstructural properties of friction stir processing (FSP) of Al–Si aluminum alloy. FSP was carried out using different compressed air and water coolants with different flow rates. The FSP tool force was measured experimentally using an especially designed load measuring system. Optical microscopy was used to probe the microstructures of the FSPed samples. The results showed that the Si particles size significantly decreases with increasing in-process cooling rate. Mechanical properties of each FSPed sample were also determined using hardness tests. Finally wear tests were conducted using a pin-on-disk tribometer.
The present work describes the influence of different carbon black nanoparticles with different concentrations on the mechanical properties of a structural epoxy adhesive cured by dielectric and thermal heating. This work was undertaken to improve the understanding of the effect of carbon black nanoparticles concentration on the stiffness (Young’s modulus), strength (yield strength) and deformation of the adhesive. Two kinds of spherical carbon black nanoparticles with different dielectric properties and sizes were used. Specimens with different amounts of carbon black were manufactured for each nanoparticle. The mechanical properties of the adhesive were measured in bulk specimens. The mechanical properties were found to vary as a function of the carbon black amount. For the dielectric cure, the strength and stiffness of the adhesive decrease as the amount of carbon black nanoparticles increases. On the other hand, the adhesive showed an increase of the deformation with an increase of the carbon black concentration. The thermal cure showed a mechanical behaviour similar as the dielectric cure, but the curing time increases substantially. A scanning electron microscopy analysis was performed to analyse the surface fracture of the adhesive. The fracture surfaces of specimens cured by dielectric and thermal heating and without nanoparticles are similar, typical of brittle adhesive. For high carbon black amount, the fracture surfaces are typical of ductile adhesive.
Free vibration study of non-uniform plates with in-plane material inhomogeneity is carried out in the present work considering geometric nonlinearity. Inhomogeneous plates where the material properties vary along only x-axis (unidirectional) and along both x- and y-axis (bidirectional) are considered. The analysis is performed for two boundary conditions namely clamped and simply supported at all edges, under the action of a transverse uniformly distributed load. The large amplitude problem is formulated using nonlinear strain–displacement relations along with a variational form of energy method. A two-step solution procedure is utilised where, in the first part the static problem is solved and undetermined coefficients are found, subsequently the dynamic problem is taken up on the basis of previously determined coefficients. Validity of the results is successfully confirmed by comparison with the works of other researchers. The analysis reveals that the amplitude and taper parameter affect the loaded natural frequencies significantly. Three-dimensional mode shapes for linear and nonlinear cases are presented along with their respective contour plots.
Joining of dissimilar aluminum alloys are widely used in automobile, aerospace and shipbuilding industries. The defect-free joining of aluminum alloys using conventional technique is a challenging task for a welding engineer. Friction stir welding has been established as one of the most promising processes for defects-free joining of aluminum alloys. In this study, a hybrid approach of grey relational analysis with principal component analysis, is applied for multi-objective optimization of process parameters for friction stir welding of dissimilar AA5083/AA6063 aluminum alloys. Three responses namely tensile strength, average hardness at weld nugget zone and average grain size at weld nugget zone, and four process parameters with three levels have been selected for the study. Taguchi method based L27 orthogonal array design matrix is used for experiments. The optimal set of process parameters using hybrid approach was found as 900 r/min of tool rotational speed, 60 mm/min of welding speed, 18 mm of shoulder diameter and 5 mm of pin diameter. Improved performance of each response was obtained from the confirmation tests at optimum level of parameters.
This paper addresses the problem of materials selection for springs used to clamp an inner shroud segment to the outer shroud block in utility and industrial gas turbine engines. Clamping is achieved through the application of an initial compressive load to the spring. However, since the spring is subjected to high temperature and oxidizing conditions, it experiences creep and surface oxidation. Both of these processes result in the loss of the compressive load within the spring with time. A material selection procedure is developed, which identifies optimum materials (design variables), with respect to the minimum loss in the clamping-spring load (objective function) for a given set of geometrical constraints (i.e. maximum size of the spring is constrained by the outer-shroud cavity which houses the spring) and functional constraints (force retention should persist over the expected life of the inner-shroud segment). Two material selection procedures are devised: (a) one, fairly rigorous and computationally intensive, based on the use of a finite element analysis; and (b) the other, less rigorous but computationally less expensive, based on the use of a simplified analytical/numerical procedure. In the absence of oxidation, the two approaches yielded different, but mutually consistent, results with identical ranking of the clamping-force candidate materials. The inclusion of the oxidation effects showed that oxidation-induced loss in the spring material increases the extent of clamping-force relaxation and may affect the ranking of the candidate materials.
Leaking in a CO2 pipeline could escalate to sudden crack propagation, due to a large temperature drop. The resulting drop in fracture toughness together with the pressure stresses at the defect plane leads to pipeline brittle fracture. The main objective of this study is to monitor and predict brittle fracture behaviour of API X70 pipeline steel by means of experimental and numerical approaches, respectively. Dynamic fracture properties of CO2 line pipe steels are generally assessed using the Charpy impact test. To this end, Charpy V-notch tests are performed at different temperatures in order to study the resistance of materials subjected to impact loading conditions. The Charpy test provides valuable indications on the impact properties of materials. Using the experimental results the ductile to brittle transition temperature curve is presented. The extended finite element method based cohesive zone approach is introduced to model the brittle fracture at low temperature. After validation of the developed model against experimental observation significant results from the simulation are graphically presented and discussed.
The present research investigates the application of artificial intelligence tool for modelling and multi-objective optimization of friction stir welding parameters of dissimilar AA5083-O–AA6063-T6 aluminium alloys. The experiments have been conducted according to a well-designed L27 orthogonal array. The experimental results obtained from L27 experiments were used for developing artificial neural network-based mathematical models for tensile strength, microhardness and grain size. A hybrid approach consisting of artificial neural network and genetic algorithm has been used for multi-objective optimization. The developed artificial neural network-based models for tensile strength, microhardness and grain size have been found adequate and reliable with average percentage prediction errors of 0.053714, 0.182092 and 0.006283%, respectively. The confirmation results at optimum parameters showed considerable improvement in the performance of each response.
It is hard to finish small slots in composite materials which have wide applications nowadays in aerospace, automobile and medical. Abrasive flow machining is a process that is suitable for such type of operations. In this paper, by using abrasive flow machining, investigation of SiC Metal Matrix Composites (MMCs) with aluminum as base material has been done. Material removal rate and change in surface roughness (Ra) are taken as response parameters. Response surface methodology has been applied to find out the effect of input parameters like fluid pressure, percentage of oil in media, grit size, concentration of abrasives, workpiece material and number of cycles on response parameters. Box–Behnken design has been preferred. Response parameters have been optimized using the desirability approach in response surface methodology. The significance of different parameters is identified using analysis of variance. An optimum combination of parameters is designed for the process. Furthermore, specimens were examined and analyzed using scanning electron microscope and X-ray diffraction techniques.
This paper presents the results of small punch creep testing (SPCT) of a vacuum plasma-sprayed (VPS) CoNiCrAlY coating (Co – 31.7%, Ni – 20.8%, Cr – 8.1%, Al – 0.5%, Y, all in wt%) carried out at 750 ℃. Coating cross-sections, after initial heat treatment, after sample clamping in the test rig prior to testing and after SPCT, were examined using scanning electron microscopy (SEM). A dual phase structure consisting of a fcc -Ni matrix and a bcc β-NiAl secondary phase was found to exist. A large number of partially melted powder particles, with a semi-continuous β layer surrounding most of the partially melted particles, were found in the coating. Pre-cracking was observed to occur around the partially melted particles after sample clamping was applied in the test rig prior to testing. This was due to the inherent brittleness of the β layer around those particles. Very short failure times were obtained from the SPCT of the specific VPS CoNiCrAlY coatings, due to the pre-existing cracks formed during sample clamping.
An analytical model for the prediction of springback in bending of longitudinally welded tailor-welded blanks of different thickness is presented in this paper. The effect of strain hardening, anisotropy and weld zone has been incorporated in the analytical model. Power law of strain hardening and Hill’s anisotropic yield criterion have been used in the development of the analytical model for prediction of springback in tailor-welded blanks. The predicted values of springback are validated with experiments on V-bending of laser-welded blanks of Extra Deep Drawing quality steel sheets. Longitudinally welded specimens of three different thickness combinations with weld line oriented at 0°, 45° and 90° to the rolling direction are tested to investigate the effect of anisotropy. The springback values predicted by the analytical model incorporating the weld properties are found to be in good agreement with the experimental results in all of the cases. The springback has been found to be maximum when the weld line is oriented at 45° to the rolling direction.
The microstructure evolution during recently developed severe plastic deformation method named repetitive tube expansion and shrinking of commercially pure AA1050 aluminum tubes has been studied in this paper. The behavior of the material under repetitive tube expansion and shrinking including grain size and dislocation density was simulated using the finite element method. The continuous dynamic recrystallization of AA1050 during severe plastic deformation was considered as the main grain refinement mechanism in micromechanical constitutive model. Also, the flow stress of material in macroscopic scale is related to microstructure quantities. This is in contrast to the previous approaches in finite element method simulations of severe plastic deformation methods where the microstructure parameters such as grain size were not considered at all. The grain size and dislocation density data were obtained during the simulation of the first and second half-cycles of repetitive tube expansion and shrinking, and good agreement with experimental data was observed. The finite element method simulated grain refinement behavior is consistent with the experimentally obtained results, where the rapid decrease of the grain size occurred during the first half-cycle and slowed down from the second half-cycle onwards. Calculations indicated a uniform distribution of grain size and dislocation density along the tube length but a non-uniform distribution along the tube thickness. The distribution characteristics of grain size, dislocation density, hardness, and effective plastic strain were consistent with each other.
Interest in cancellous bone analogous materials is driven by the development of tissue engineering and biomaterials. For the past decade, the research focus has been centered on biodegradable materials, in which the ability of the material to safely degrade in the human body while retaining sufficient qualities during service is conveniently cost-effective and less morbid. Among others, magnesium and its alloys have presented the best qualities especially as load-bearing biomaterials. In this article, the promising details of porous magnesium and its alloys as a cancellous bone analogous material developed during the past 10 years are highlighted. The manufacturing processes, mechanical performance, and biocompatibility of porous magnesium and its alloys are discussed. The Achilles’ heel of current evaluation was identified. Further, a few prospective developments of porous magnesium and its alloys are put forward with advanced desirable qualities as a cancellous bone analogous material.
In this study, the production and characterization of A5083–Al2O3–TiO2 hybrid surface nanocomposite by friction stir processing have been investigated. The effect of different ratios of nanosized Al2O3 and TiO2 particles on microstructural and mechanical properties was investigated. A threaded cylindrical hardened steel tool was used with the rotation speed of 500 r/min and travel speed of 56 mm/min and a tilt angle of 3°. Microhardness of base metal and treated surfaces as well as tensile strength was evaluated. The samples were characterized by means of optical and scanning electron microscopy. The results showed that the maximum tensile strength and hardness value were achieved for a mixture of Al2O3 and TiO2 in the ratio of 25–75, respectively. The microhardness and tensile strength were respectively increased by 50% and 182% while ductility was reduced by 60%.
The present work focuses on exchanging the sodium in Na-bentonite by single (Mg, Zn and Sr) and double (Zn–Mg, Mg–Sr and Zn–Sr) cations to induce the cation-exchange process. Different cation-exchange bentonites (CEBs) were used as reinforcing fillers with different loadings in acrylonitrile–butadiene rubber (NBR) composites. Curing characteristics, mechanical properties, morphology and swelling behaviour were determined. The study revealed that the performances of Mg bentonite and Mg–Sr bentonite were the best among the tested groups, while Sr bentonite showed the least performance, indicating that addition of Mg deteriorates the reinforcing efficiency of Sr. Moreover, it was observed that the preparation of some CEBs co-intercalated with a surfactant (cetyl trimethyl ammonium bromide (CTAB)) using cation-exchange process was done, and in this part there was a focus on the effect of CTAB surfactant content ratio (0.5CEC) on the CEBs and their influence on the properties of NBR composites.
Nitinol (NiTi) is categorized as a smart material which is highly recognized material for medical and other engineering applications. The behaviour of NiTi can be modified by altering the composition, modifying the porosity and applying external thermal and mechanical treatment. Due to high composition sensitivity, there are several impediments in fabrication of NiTi with conventional techniques which impel the use of additive manufacturing methods. But due to very high cost of equipments, these processes have not been commercialized till now. This paper presents a review on applications, manufacturing NiTi alloy and its various production routes from conventional to rapid prototyping, porous NiTi, effect of additives on properties of the alloy and its challenges.
Surface turbulence during the filling of the mold triggers the entrainment of oxide films, which appears to be detrimental to the soundness of the final casting. Nonpressurized and bottom-gating systems have been employed in order to avoid such casting defects by reducing the surface velocity of the liquid metal. However, recent studies have shown that the melt front velocity in the mold entrance may exceed the critical value in the nonpressurized and bottom-gating systems. Therefore, a study was conducted on numerical simulation melt flow pattern in nonpressurized and bottom-gating systems. It was noted that the liquid metal enters the gate and then mold cavity with a higher velocity by formation of dead zones and vortex flows in runner's end. Therefore, the current designs based on conventional gating system ratio seem to be not optimized and unable to avoid the surface turbulence. Numerical results were in complete agreement with experimental observations. Understanding the reasons for occurrence of the surface turbulence in nonpressurized and bottom-gating systems provides information on the required steps to improve the design of the gating systems and minimize the entrainment of oxide films during the filling of the mold.
The material selection of prostheses in developing countries is currently biased towards what is readily available and ignores important criteria such as patient comfort and structural strength. In this study, the ELECTRE III multiple attribute decision-making method was applied to the material selection of a paediatric prosthetic knee. Light metals were considered as candidates for selection. While composites are light, they are not suitable for use in components with sliding and mating surfaces such as a prosthetic knee. Plastics are prone to failure. Candidate materials were evaluated on criteria related to patient fatigue and comfort, structural stability and material cost. The patient fatigue and comfort requirement was evaluated using material density as the weight of the prosthesis affects the comfort level. Finite element analyses simulating the ISO 10328:2006 standard for structural testing of lower limb prostheses were used to evaluate the structural strength suitability of the candidate materials. The present day prices of the raw material of the candidates were used as an index of material cost. Wrought aluminium alloy aluminium 7175 was ranked highest while titanium alloys were ranked below these due to their higher cost. Cast aluminium alloys ranked lowest due to their poor structural performance. The study, using ELECTRE III, a rigorous multi-criteria decision analysis method, shows that aluminium 7175 is the optimal light metal material for a paediatric prosthetic knee.
Fibre composite guardrails are increasingly being used to ensure safety of workers from fall-from-height incidents due to its high strength, high corrosion resistance and low maintenance. In this study, the structural behaviour of pultruded glass fibre-reinforced polymer (GFRP) guardrail was evaluated following AS1657-1992. GFRP guardrail systems mounted on top and side of a steel beam with different joint connectors are loaded horizontally to top of the guardrail post and to the middle of the guardrail member. The results showed that the guardrail system with joints connected with either polypin or rivets combined with epoxy exhibited 20% higher failure load and almost double the stiffness than those connected using polypin or rivets alone. The side-mounted guardrail failed due to failure of the base connector while the guardrail mounted on top of the beam failed at the joints indicating that the structural behaviour of GFRP guardrail system is affected mainly by the type of joints.
Temperature and forces in friction stir processing (FSP) induced by process input parameters play a critical role in successful welding. In this investigation, the effect of the process parameters on the axial and longitudinal forces and temperature history of the process were investigated. The temperature distribution during the FSP was determined by placing thermocouples in the workpiece and measuring the temperature during the process. The tool forces were investigated experimentally using an especially designed load measuring system. The pin shape, rotational speed and traverse speed were the parameters taken into consideration. It was observed that increase in tool traverse speed or decrease in rotational speed leads to increase in both tool axial and longitudinal forces.
In the present study, the effect of various factors of friction stir welding including rotational and traverse speeds of tool and in fact, the amount of the heat transferred within welding was evaluated on the resistance to fatigue crack growth and fracture toughness in different zones of welding copper sheets. In order to better assess these two properties, other mechanical properties such as tensile strength and hardness were also studied and the microstructure of different zones of welds was investigated using optic and electron microscopies. By doing this study, it became clear that the less the heat transferred to the plunging during the welding process, the better properties the resulting welds will have which well justifies the use of cooling in this study. Transferring heat to plunging causes the growth of grains in various zones and can cause the fatigue crack growth in heat-affected zone to increase averagely about 4.2 times the base material for different K. In contrast, the occurrence of dynamic recrystallization in the stir zone as well as fragmentizing and alignment of grains in this zone can increase the resistance to fatigue crack growth up to 9-fold the resistance of the base material. The other interesting result of this study was that although the properties of stir zone improve by increasing the number of welding passes, the properties of its weakest zone i.e. the heat-affected zone will decline.
This paper describes a decision support approach for selecting construction materials in the field of petrochemistry. The correct selection of construction materials is the basis for the provision of durability, long lifetime, and the safety of the designed and upgraded equipment. The proposed hybrid approach is based on the joint application of case-based reasoning and multi-criteria decision-making methods, particularly the aggregation and ranking alternatives nearby the multi-attribute ideal situation (ARAMIS) and aggregation of individual ranking/ complex of aggregation of individual ranking (AIR/CAIR) methods are used. In turn, ARAMIS enables the processing of individual preferences, which are represented in the form of numeric and verbal estimates, and AIR/CAIR is used for processing rankings (strictly or partially ordered sets of alternatives). The primary advantage of this approach is that it considers the experience of previous successful solutions of the materials selection problem, demonstrates the validity of the obtained results using the mathematical theory of multi-criteria decision making and explains the decision making process. The approach is implemented in the form of the expert system. The case model, algorithms, and an illustrative example of application of the proposed approach are also presented.
TiNiCu shape memory alloys have superior properties as compared with NITINOL due to their greater ductility, reduced hysteresis temperature range, and quick actuation response. The present article investigates the surface and subsurface modifications occurring due to wire electro discharge machining of Ti50Ni50-xCux shape memory alloy. The machining experiments were performed considering the pulse on time, pulse off time, and servo voltage as the process parameters. The influence of these parameters was studied on the material removal rate, surface roughness, recast layer thickness, microhardness, and phase changes in the machined surface. Longer pulse on time causes greater discharge energy, hence leading to higher material removal rate, surface roughness, and recast layer thickness. The machined surface hardness increased up to 900 Hv, which is about 59% increase with respect to the base material for longer pulse on time due to the recast layer thickness and the formation of oxides. A phase change on the machined surface was observed to cause the shape recoverability of the alloy. The microstructure, composition through EDAX, and the phase changes of the machined surface are also discussed in the article.
The article presents microstructures and mechanical properties of near-β Ti-10V-2Fe-3Al titanium wrought alloy after two differentiated processing cycles. The assumed processing paths involved high strain rate hot deformation in β-phase range, followed by solution treatment with variation of cooling rate and subsequent single or double aging. To estimate the effects of the assumed treatment cycles, optical microscopy and scanning electron microscopy microstructure analysis was conducted, with special attention paid to evolution of alpha precipitates in consecutive stages of processing and their role in grain refinement. The correlation between tensile properties and grain size, as well as the amount of precipitates amount was found to be connected with alpha-plates’ size and morphology. It was concluded that in case of Ti-10V-2Fe-3Al titanium alloy, proposed cycles of thermomechanical processing allow reduction of inhomogeneous recrystallization resulting in necklace substructure. On the other hand, high strain rate promotes mechanical properties improvement, as it favors fragmentation of continuous grain-boundary α precipitates.
In the present work, the optimization of Activated TIG (A-TIG) welding process parameters to achieve the desired weld bead shape parameters such as depth of penetration, bead width, and heat-affected zone (HAZ) width have been carried out using response surface methodology (RSM). The main problem faced in fabrication of weld joints is the selection of optimum combination of input variables for achieving required quality of welds. This problem can be solved by development of mathematical model and execution of experiments by RSM. Central composite design of RSM has been used to generate the design matrix for generating data on the influence of A-TIG welding process parameters. The input variables considered were welding current, torch speed, electrode tip angle, and arc gap. The response variables considered were depth of penetration, bead width and HAZ width. A second-order response surface model is developed for predicting the response for the set of given input process parameters. Then, numerical and graphical optimization is performed using RSM to obtain the desired depth of penetration, bead width, and target HAZ width using desirability approach.
This paper develops a new physically based model to investigate face centered cubic (FCC) metals and alloys under high strain rate loadings (\gt104 s–1) which includes kinematics and constitutive equations for the propagation of elastic and steady plastic waves. The model’s formulations are based on the rate of the conservation energy law that includes the rate of the input energy, internal energy, and entropy generation. This formulation is obtained by incorporating the viscous drag effects and associating the entropy generation to the generation, glide, and annihilation of dislocations. The model is used for 6061-T6 aluminum alloys and the results are verified with the published theoretical models and experimental tests. Also, the effect of different parameters, such as the particle velocity, shear flow stress, shear strain rate and temperature are investigated. As a result, the presented model shows good capability in describing the mentioned parameters.
New materials are traditionally developed using costly and time-consuming trial and error experimental efforts. This is followed by an even lengthier material-certification process. Consequently, it takes 10–20 years before a newly discovered material is commercially employed. An alternative approach to the development of new materials is the so-called materials-by-design approach within which a material is treated as a complex system and its design and optimization is carried out by employing computer-aided engineering analyses, predictive tools and available material databases. In the present work, the materials-by-design approach is utilized to redesign a grade of high-strength low-alloy steels with improved mechanical properties (primarily strength and fracture toughness), processability (e.g. castability, hot formability and weldability) and corrosion resistance. Toward that end, a number of material thermodynamics, kinetics of phase transformations, and physics of deformation and fracture computational models and databases have been developed/assembled and utilized within a multidisciplinary, two-level material-by-design optimization scheme. To validate the models, their prediction is compared against the experimental results for the related steel high-strength low-alloy 100. Then the optimization procedure is employed to determine the optimal chemical composition and the tempering schedule for a newly designed high-strength low-alloy steel grade with enhanced mechanical properties, processability and corrosion resistance.
The composite wear resistant cladding of nickel-based powder matrix and 10% SiC powder as reinforced was developed through microwave hybrid heating on martenisitic stainless steel (SS-420) substrate. The development of the clad has been carried out by using a domestic microwave applicator of frequency 2.45 GHz and 900 W power level. The microstructural and mechanical characterizations of the developed clad were carried out by using scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and Vicker’s microhardness analysis. Results revealed that clads of approximately 1.25 mm thickness were developed with significantly low porosity (~1.10%). The scanning electron microscopic results show that the microstructure of clad exhibits typical cellular-like structure. The metallurgical bonding between clad and substrate surface was obtained with partial dilution. The complex carbides of chromium and silicides of chromium, iron, and nickel phases were identified in the clad region by XRD study, which may enhance the Vicker’s microhardness of the clads significantly. The average Vicker’s microhardness of the developed clad was in the range of 652 ± 90 HV.
This paper presents the results of an experimental investigation on machining of micro-hole during electrochemical micromachining (ECMM) of stir-cast hybrid aluminum/(alumina + silicon carbide + carbon particulates) metal matrix composite. An ECMM set-up was developed and utilized for carrying out the experimental investigation. The supply current (Ip), supply voltage (v), pulse-on time (Ton), pulse-off time (Toff), electrolyte concentration (EC), and electrolyte flow rate (FR) were selected as process parameters. The effect of process parameters on material removal rate (MRR), electrode wear rate (EWR), surface roughness height (SR), taper cut (TC), over cut (OC), and micro-spark-affected zone (MSAZ) were analyzed through various graphs. The surface characteristics of the micro-drilled holes were analyzed using energy dispersive X-ray spectroscopy and scanning electron microscope techniques. Experimental results revealed that the MRR, EWR, TC, OC, and MSAZ increase with an increase in supply current, voltage, and pulse-on time. The optimal parametric combination for high MRR with low TC, OC, and MSAZ was found at 1.5 A supply current, 13 V supply voltage, 10 µs pulse-on time, 10 µs pulse-off time, 15 g/L electrolyte concentration, and 0.2 L/min electrolyte flow rate.
This paper presents a new experimental test for determining the stress–strain curve and the fracture toughness of sheets to be used in sheet-bulk metal forming (SBMF) applications. The test is based on the utilization of double-notched specimens loaded in shear and combines the plane stress loading conditions of sheet metal forming with the three-dimensional plastic flow conditions of bulk metal forming, which are commonly found in SBMF processes. The methodology to obtain the stress–strain curve involves calculation of the shear stresses and strains along the two symmetric plastic shear zones of the test specimens up to point where cracks start to propagate along the ligaments that connect each pair of opposite notches. The determination of fracture toughness involves characterization of the evolution of load with displacement for a number of test cases performed with specimens having different ligaments between the two symmetric opposite notches. The work is performed on aluminium alloy EN AW 5754 H111 sheets with 5 mm thickness and the results obtained by means of the new proposed test are compared against those from conventional mechanical and fracture characterization tests.
This article is focused on the study of the contribution of aramid fibers in a hybrid carbon–aramid fiber twill weave used to reinforce epoxy resin. To evaluate the influence of the aramid fibers, a comparative study between carbon and carbon–aramid woven–reinforced composites, considering the mechanical behavior of both materials under several loading conditions, is performed. The tests used in this study are meant to analyze the effect of aramid reinforcements on the composite stiffness, strength, impact, and fracture performance. Higher values of energy absorption and fracture toughness were exhibited by the carbon–aramid composite. The mechanical tests performed indicated that the aramid phase present in the hybrid carbon–aramid composite induced an important enhancement on the impact (37.9% in energy absorption) and fracture resistance (12.7% for fracture initiation and 43% for steady state regime), compared to small reductions on the material stiffness. In addition, the ultimate strain and the through thickness compression strength were favorably affected, with an increase up to 19.5% and 8.3%, respectively, by the presence of aramid fiber that presents a more ductile response with respect to the carbon reinforcement.
The mechanical properties of hardened AISI 52100 bearing steel such as flexural strength, microhardness and Young’s modulus are considerably influenced by the austenite content retained in the microstructure. A microstructure-sensitive finite element simulation approach is presented which considers the effect of retained austenite to estimate the mechanical properties. The austenite grain size is derived as a function of austenitising temperature and holding time using a modified Arrhenius type equation. The simulation strategy involves division of the two-dimensional domain using triangular elements such that a group of six neighbouring triangular elements represented a hexagonal grain of calculated size. Material inhomogeneity is introduced by enforcing austenite properties to a fraction of the elements equal to the volume percent of retained austenite in the steel. The predictions from the simulation approach for 8% and 20% retained austenite volume fractions matched well with earlier experimental results.
To design novel high-performance aluminium alloys, the properties and microstructure of Al–4.2Cu–1.4Mg alloy containing Zn and Li have been investigated by tensile tests, fatigue crack propagation test, slow strain-rate tensile test, Kahn tear test, scanning electron micrography and transmission electron micrography. The stress corrosion cracking resistance and toughness of Al–4.2Cu–1.2Mg alloy can be markedly improved by small Zn addition. Independent Li addition has no significant effect on the corrosion resistance of Al–4.2Cu–1.2Mg alloy, but the tensile strength is improved and the fatigue crack propagation is restrained. Small Zn addition promotes the precipitation of S' phase during age treatment, and the grain boundary precipitates are scarcer than those of the base alloy. The co-effect of Li and Zn addition promotes the fine and dispersed precipitation of the S' (non-equilibrium Al2CuMg) phases in Al–4.2Cu–1.2Mg alloy. The comprehensive performance (the fracture toughness, tensile properties, stress corrosion resistance and fatigue crack propagation resistance) of Al–4.2Cu–1.2Mg alloy with 0.25% Zn and 1.0%Li is outstanding. This alloy could lay the foundation for the design of new aluminium alloys.
Bamboo fibre is becoming more important as reinforcement in polymer composites owing to its environment sustainability and cost effectiveness. This study examines the performance of bamboo/polyester concretes under impact loading. Specimens at fibre volume fractions of 40 vol.%, 50 vol.% and 60 vol.% and 3 mm, 7 mm and 10 mm fibre lengths were fabricated. Results showed that the optimum impact resistance was attained at 50 vol.%/10 mm, with 16.6 times higher compared to neat polyester. Scanning electron micrographs revealed that the failure mechanisms include matrix cracking, fibre/matrix debonding, fibre pull-out, fibre end damage, fibre splitting and sand particles debonding. In addition, by relating the experimental results to a theoretical model, the damage zone size was found to increase with the fibre length except at 60 vol.%/10 mm, which could be due to fibre–fibre interaction. Results suggest that bamboo fibre is a good candidate to enhance the impact resistance of polyester concrete.
Cohesive zone elements used in finite element analysis are a reliable way to design and predict the behaviour of the joint. The characterisation of the traction separation law used in these models is done using tensile and fracture tests, and the parameters of such laws depend on humidity and temperature. Water diffusion tests are therefore necessary, which are dependent on specimen geometry, meaning a bigger specimen takes longer to fully saturate. To solve this problem and increase the efficiency of the ageing process, smaller tensile bulk and double cantilever beam (DCB) specimens are necessary. Another advantage of smaller DCB specimens is that they can be tested in smaller high-temperature chambers, where normal DCB specimens do not fit. Smaller geometries of the bulk tensile and DCB tests are analysed, and a proposed geometry for each test is shown to produce very satisfactory results, validating the use of these specimens.
Prediction of fatigue lives of a rubber mount necessitate formulation of models for estimating fatigue life of the rubber materials used in the mount. Moreover, the prediction accuracy of the model is strongly dependent upon the choice of damage index that are based on different strain, energy or stress measures in the vicinity of critical locations of the rubber mount. In this study, relative performance of models employing different damage indices are evaluated for prediction of fatigue lives of rubber material and a drive-train rubber mount. A combined stress and an effective stress function are proposed as a damage index for predicting fatigue lives of rubber materials and the mounts. Different damage indices, identified from the finite element models of the rubber dumbbell cylindrical specimen are applied for formulations of fatigue life prediction models. The model parameters are identified from the measured data acquired for the rubber dumbbell cylindrical specimen under 31 different uniaxial displacement loads, using least squared error minimization technique. The identified models employing different damage indices are subsequently applied for predicting fatigue lives of rubber mounts under different magnitudes of loads applied along two different directions. The correlations of the predicted lives of the rubber mount from the models employing different damage indices with measured fatigue life data were subsequently investigated for the rubber mount subject to different load conditions. It is shown that the models identified for the rubber material could be effectively used for predicting fatigue lives of the mounts, which are made of same material. The fatigue lives predicted by the models considering either effective stress or combined stress as the damage index correlated with the measured data within a factor of two for the two, suggesting that stress-based damage indices could yield more accurate predictions of fatigue lives of typical mounts.
The main goal of this paper is to assess the mechanical damage in solid rigid foam materials with similar mechanical properties to the human bone induced by the cutting parameters. In the present study, a three-dimensional dynamic finite element model was developed to simulate the drilling process in solid rigid foam materials and it was validated with experimental results. Using an explicit dynamic numerical simulation, it is possible to obtain large structural deformation with high load intensity in short time frame. The developed model is used to study the effects of different high intensity loads distribution in the solid rigid foam materials. Laboratory tests were produced using biomechanical test blocks instrumented with strain gauges in different surface positions during the drilling process. The comparison between the numerical and the experimental results enables the evaluation and improvements of the cutting process. It was concluded when the feed-rate is higher, the stresses and strains in the solid rigid foam material are lower. The developed numerical model proved to be a great tool in this kind of analysis and available to use in forthcoming tests.
This research work investigates friction and wears behaviour of CaO filler / particulate reinforced ZA-27 alloy composites. Pin-on-disk tribometer confining to ASTM G 99 standard with EN-31 hardened steel disc was used to simulate the tribological performance experimentally. The tribological parameters were evaluated over a normal load range of 5–45 N, sliding velocity of 1.047–5.235 m/s., sliding distance of 500–2500 m, environment temperature of 25–45℃ and filler content range of 0–10 wt%. The various alloy composites were fabricated under vacuum environment by high-temperature gravity casting technique. The steady-state specific wear rate and coefficient of friction were evaluated under different boundary conditions and thereafter Taguchi design of experiment methodology was adopted to compute the experimental specific wear rate of the proposed alloy composites. The dynamic mechanical analysis and thermo-gravimetric analysis study were also performed in order to observe the thermal characteristics of the composites at higher temperature. Finally, the surface morphology of the worn samples was performed using field-emission scanning electron microscope to understand the wear mechanism prevailed at rubbing surfaces and then atomic force microscopy analysis was studied to evaluate the surface profile of the worn sample. At the end, energy-dispersive spectrometer analysis was also performed to find out the elemental compositions of the worn alloy composites.
This article explores the quality characteristics of laser curve cutting of metal matrix aluminium 5052 alloy reinforced with SiC particles. These alloys are extensively used in aerospace industries due to their unique mechanical properties. The response surface methodology has been used to design the mathematical models with respect to input and output characteristics parameters. The desirability function approach has been used to optimize the input parameters like cutting speed, laser power, stand-off distance, nozzle diameter, nitrogen gas pressure, percentage of reinforced SiC particles, arc radius by considering multiple-performance characteristics. The various quality aspects of machined specimens were analysed using optical microscope, scanning electron microscopy, X-ray diffraction and energy-dispersive X-ray analysis techniques. The response surface methodology predicted models were validated by performing various confirmatory experiments. The percentage of error for the dross height, kerf taper and kerf width was found to be 4.62%, 6.55% and 5.04 % which signifies that predicted model is adequate.
The objective of the present study is to investigate and compare the strength of single pin joints made with glass fiber-reinforced epoxy laminates containing two different nanoparticles, i.e. nanoclay and nano TiO2, with bare composites. The analysis has been done both experimentally and numerically. Single-hole pin-loaded specimens were tested for their tensile strength and the distance from the free edge of the specimen to the diameter of the first hole (E/D) ratio, width of the specimen to the diameter of the holes (W/D) ratio were evaluated. The influence of these geometry parameters on the strength of the pin-loaded composites was investigated. It was found that the bearing strength of pin joints increased with the addition of nanoclay as compared to that of nano TiO2.
Laser beam machining is one of the most widely used advanced processing techniques, which can be applied to compound materials. As a large number of photons are absorbed into the composite, the subsequent local heat storage, charring and potential delamination make the study for the effect of laser on complex materials become significant. In this paper, a carbon fiber epoxy composite laminated sheet is irradiated by continuous wave chemical oxygen iodine laser. The peak temperature of front surface, the temperature distribution of rear surface, and the appearance of ablation zone are presented. Further, based on the birth–death elements technique of finite element method, a three-dimensional model for simulating the transient temperature distribution and material removal has been developed under the same condition. The results reveal that the peak temperature of irradiated region ranges from 2800 K to 3100 K, and the center point shows a higher temperature rise rate than the surroundings in the irradiated zone. The measured data and predicted data are in a good consistency, which suggests that the numerical model is appropriate for simulating laser ablation of carbon fiber epoxy composites.
In this study, 6 mm thick AA6061-T6 alloy was friction stir-welded at different traveling speeds while Al2O3 nano-particles were incorporated between adjoining plates. All joints were investigated macro- and micro-structurally. In addition, distribution pattern of Al2O3 nano-particles in the stir zone was observed via scanning electron microscopes. Although the specimen friction stir-welded at 40 mm/min exhibited the most homogeneous particles distribution, friction stir welding at 1600 rpm and 45 mm/min yielded highest tensile strength. Fractographs achieved from tensile test specimens were in close agreement with corresponding percent elongations. Surprisingly, the foregoing specimen exhibited inferior hardness to the as-received AA6061-T6 alloy. Accordingly, it was concluded that dissolution of strengthening precipitates dominated the effect of hard reinforcement particles on enhancement of hardness value. As a result of Al2O3 nano-particles introduction, on the other hand, wear resistance improved tremendously.
Magnesium alloys are increasingly accepted in automobile industry owing to their greater strength-to-weight ratio. These qualities lead to less vehicle weight and better fuel economy. Therefore, in the present work an effort has been made to develop a new Mg alloy system that exhibits greater ductility together with greater mechanical strength. Misch metal is added in Mg-based alloys to investigate the changes in mechanical properties. The microstructure of alloys Mg–4Al–3Zn–3Sn–3Pb (H1) and Mg–4Al–3Zn–3Sn–3Pb–0.5MM (H2) are dendritic in nature while for Mg–3Zn–3Sn–3Pb–2Si (H3) the "Chinese script" Mg2Si intermetallic structure was obtained. The ultimate tensile strength and elongation of Mg–4Al–3Zn–3Sn–3Pb–0.5MM (H2) alloy are about 40% and 100 % higher than that of H3 alloy. The ultimate tensile strength, yield strength, and percentage elongation of H2 alloy are 170 MPa, 44 MPa, and 3.4%, respectively.
This paper proposes a technology for joining polymer and metal tubes by their ends at room temperature, which is an alternative to structural bonding and mechanical couplings. The technology is built upon a two-stage tube forming process in which the metal tube is firstly expanded with a mandrel and, subsequently, assembled and locked by compression beading with the polymer tube by means of localized plastic instability. The presentation provides details on the tooling system and on the experimental and finite element analysis that were carried out during the development of the proposed technology. Special emphasis is placed on establishing the role of process parameters in the joinability of polymer and metal tubes and determining the maximum internal pressure that these hybrid joints are capable to withstand, without leakage.
The main objective of this study is to develop a CAE-based application with a convenient GUI for identification and verification of material parameters for hyperelastic models available in the current release of the FE code ANSYS Mechanical APDL. This Windows application implements a two-step procedure: (1) fitting of experimental stress–strain curves provided by the user; (2) verification of the obtained material parameters by the solution of a modified benchmark problem. The application, which was developed using the Visual Basic.NET language, implements a two-way interaction with ANSYS as a single loop using the APDL script as input and text, graphical and video files as output. With this application, nine isotropic incompressible hyperelastic material models are compared by fitting them to the conventional Treloar’s experimental dataset (1944) for vulcanised rubber. A ranking of hyperelastic models is constructed according to model efficiency, which is estimated using fitting quality criteria. The model ranking is done based upon the complexity of their mathematical formulation and their ability to accurately reproduce the test data. Recent hyperelastic models (Extended Tube and Response Function) are found to be more efficient compared to conventional ones. The verification is done by the comparison of an analytical solution to an FEA result for the benchmark problem of a rubber cylinder under compression proposed by Lindley (1967). In the application, the classical formulation of the benchmark is improved mathematically to become valid for larger deformations. The wide applicability of the proposed two-step approach is confirmed using stress–strains curves for seven different formulations of natural rubber and seven different grades of synthetic rubber.
The creep rupture properties of AISI 347 austenitic stainless steel foil used in compact recuperators have been evaluated at 750 ℃ in the stress range of 54–221 MPa to establish baseline behavior for its extended use. The creep curve of the foil shows that the primary creep stage is brief and creep life is dominated by tertiary creep deformation with rupture lives in the range 3–433 h. Power law relationship was obtained between the minimum creep rate and the applied stress with stress exponent value of n = 4.25. The creep damage tolerance parameter for specimen tested at 750 ℃ and 54 MPa indicates that creep fracture takes place by precipitate coarsening mechanism. Nucleation of voids mainly occurs at second-phase particles (Cr23C6 carbides). The improvement in strength is attributed to the precipitation of fine niobium carbides in the matrix which prevents dislocation movement of the microstructure.
The paper presents the investigations on obtaining dual phase fillers with preset silica content running a successful impregnation of two completely different types of conventional carbon black with silicasol. The hybrid fillers studied were characterized by atomic absorption spectroscopy and inductively coupled plasma–optical emission spectroscopy. The total pore volume, the average pore diameter, the specific surface area, the oil absorption number, and iodine adsorption of the fillers were also investigated. The distribution of both phases within the hybrid filler obtained and their interpenetration were investigated with scanning transmission electron microscopy-energy dispersive X-ray spectroscopy. The hybrid products obtained were investigated as reinforcing fillers of natural rubber-based composites. The results obtained show that the suggested impregnation with silicasol of conventional carbon black is a perspective method for preparation of carbon-silica dual phase fillers. The method provides an easy control over the quantitative ratio between the two phases. The fillers thus prepared do not change significantly the curing and mechanical characteristics of the vulcanizates, but improve their thermal aging resistance. The isolation of the carbon black aggregates by the silica phase, and the interpenetration of the two phases is a prerequisite to obtain elastomer composites of good mechanical and microwave properties suitable for producing of microwave shielding devices.
Deformation at elevated temperature of Ti6Al4V sheets may represent a process route alternative to machining and Additive Manufacturing (AM) operations to produce biomedical implants characterized by a high surface-to-thickness-ratio. The paper investigates the mechanical and microstructural behaviour at elevated temperature of Ti6Al4V sheets whose surface was properly modified through thermo-electro-chemical processes to enhance the roughness, and therefore osseointegration, as well as bioactivity, to meet the requirements imposed by the specific biomedical application. After the surface characterization, tensile tests were carried out at different temperatures on samples modified on the surface in order to investigate the ductility, microstructure and micro-hardness after deformation and the effect of the surface treatments on them. The optimal surface treatment and deformation temperature were identified, which assured, at the same time, significant ductility increase compared to room temperature, and preservation of the roughness and bioactivity characteristics.
Improving quality in today’s complicated industrial systems is gaining more and more importance every day. Since applying these systems costs a lot, companies should try to offer the best outcomes and processes possible. One of the products most applied is Tailor Welding Blanks, which is widely used in automobile, aerospace, and other industries. One of the best methods of producing Tailor Welding Blanks is Friction Stir Welding. Using this technology, sheets dissimilar in material and thickness can be joined. In this paper, the possibility of welding thin sheets of 5083-H12 and 6061-T6 aluminum alloy by Friction Stir Welding with the thickness of 1.5 mm is examined. To detect the impact of Friction Stir Welding parameters, i.e. rotational speed (r/min), linear speed (mm/ min), shoulder diameter (mm), and tilt angle (°), a Box-Behnken design was used and using multiple Response Surface Methodology values of robust optimization of tensile strength and elongation were derived. The optimization and experiment results were then compared. The results of the comparison showed a good correspondence.
The purpose of this paper is to develop 7 wt% yttria stabilized zirconia (7YSZ) thermal barrier coatings by optimization of the atmospheric plasma spraying process parameters. Multiple-performance characteristics, such as coating thickness and surface roughness were considered for optimization. Eighteen experimental runs based on the L18 orthogonal arrays of the Taguchi method were used to show the best conditions among the plasma spraying parameters. Thereafter, best possible process parameters were obtained by the analysis of variance using grey relational analysis as the quality guide. Results signify the application possibility of the grey-based Taguchi technique for continuous development of quality coating in the area of advanced manufacturing technology.
Bloodhound SSC is a vehicle that aims to raise the World Land Speed Record to over 1000 mile/h in Hakskeen Pan, South Africa. Its lower chassis is a riv-bonded fabrication made using steel sheet for skins and aluminium alloy machinings for bulkheads. Fasteners alone were enough to satisfy the lower chassis structural requirements; however, Redux 312/5 epoxy adhesive was used to increase the stiffness of the structure and limit potential corrosion due to water and soil ingress. The use of dissimilar metals in the chassis could lead to panel buckling during elevated cure temperatures, meaning a low adhesive cure temperature of 80–90 ℃ was required to minimise this risk. As the cure pressure for the lower chassis adhesive was achieved using only rivets, the variation of cure pressure was experimentally investigated and found to be within the manufacturer’s recommendations for large sections of the lower chassis. Tensile testing indicated the chassis could be cured at 80 ℃ instead of the optimum 121 ℃, without significant loss of mechanical strength. A thermal characterisation of the adhesive was conducted using dynamic mechanical analysis and differential scanning calorimetry. A variety of cure profiles was investigated and resulted in a cure profile that maximised the glass transition temperature (Tg). An increase in cure duration to 8 h was recommended, which resulted in an increase in Tg by 15–24 ℃ to 83–92 ℃.
In this work, silicon nitride nanostructures were prepared by a reactive sputtering technique employing, a novel design of closed-field unbalanced dual magnetron system. The optical properties of the prepared nanostructures were studied by their absorption and transmission spectra in the range of 200–800 nm. As well, the structural properties of these structures were studied to determine the optimum geometry of the employed closed-field unbalanced dual magnetron configuration. The produced Si3N4 nanostructures showed high absorption in the ultraviolet wavelength region (<200 nm) in addition to an absorption band centered at 389 nm. The energy gap of the prepared samples was found to be 5.2 eV of allowed and direct type. Structural results showed that the prepared samples were amorphous with average particle size of 20–30 nm, average particle diameter of 99.22 nm and average roughness of 0.777 nm. In this technique, low cost, high purity and homogeneous surfaces can be prepared by the effective control of the operation parameters, especially the geometry of closed-field unbalanced dual magnetron configuration.
In the present work, multi-length-scale physical and numerical analyses are used to derive a SiC/SiC ceramic matrix composite (CMC) material model suitable for use in a general room-temperature, finite element-based, structural/damage analysis of gas turbine engine components. Due to its multi-length-scale character, the material model incorporates the effects of fiber/tow (e.g. the volume fraction of the filaments, thickness of the filament coatings, decohesion properties of the coating/matrix interfaces, quality, as quantified by the Weibull distribution parameters, of the filament, coating, and matrix materials, etc.) and ply/lamina (e.g. the 0°/90° cross-ply vs. plain-weave architectures, the extent of tow crimping in the case of the plain-weave plies, cohesive properties of the inter-ply boundaries, etc.) length-scale microstructural/architectural parameters on the mechanical response of the CMCs. To identify and quantify the contribution of the aforementioned parameters on the material response, detailed numerical procedures involving the representative volume elements and the virtual mechanical tests are developed and utilized. The resulting homogenized turbine-engine component-level material model is next integrated into a user-material subroutine and used, in conjunction with a commercial finite element program, to analyze the foreign object damage experienced by a toboggan-shaped turbine shroud segment. The results obtained clearly revealed the role different fiber/tow and ply/lamina microstructural parameters play in the structural/damage response of the gas-turbine CMC components.
Laser forming, which is categorized as a thermal forming process, is used in forming and bending of metallic and non-metallic sheets. Laser beam irradiation causes a localized temperature increase and a localized mechanical strength decrease. In this article, the effects of four process parameters, comprising laser power, scan velocity, the number of scan passes, and sheet thickness, on laser forming of Al6061-T6 sheets are studied. A design of experiment, including response surface methodology, is carried out to limit the experimental runs and costs and to identify the parameter effects on the bending angle of the sheet. Experiment results show that bending angle increases due to the decrease of scan velocity and sheet thickness. In addition, laser power and number of scan passes have a direct relation with a final sheet forming.
The high cycle fatigue tests of high-strength austempered ductile iron of grade 1200/850/04 (ASTM 897 M-06) were conducted by the high frequency fatigue machine. The results show that the S–N curve decreases continuously and there is no conventional fatigue limit at 107 cycles. According to the fracture surface observations, at short fatigue life region the specimens fail from defects at specimen surface and at long fatigue life region the specimens fail from internal defects with fish-eye area around it. According to the defect sizes measured in the standard inspection areas of the material, the maximum defect size evaluated by the statistics of extreme values method is in accordance with that of the fatigue test results. Meanwhile, it is obvious that the fatigue strength of austempered ductile iron is influenced by the original defect size and the fatigue limit can be well evaluated by the Murakami equation.
In this article, the static and the free vibration behavior of laminated woven glass/epoxy composite plate have been investigated numerically and validated through subsequent experimentation. The laminated composite shear deformable plate has been modelled mathematically using two different higher-order kinematic theories and the commercial finite element package (ANSYS). The domain has been discretized using the finite element steps and the desired responses (deflections and frequencies) are computed numerically using homemade computer code developed in MATLAB environment. The validity and the convergence behavior of developed models have been established by comparing the responses with those available published literature, simulation and the corresponding experiment. Finally, the effects of geometrical and material parameters (thickness ratio, modular ratio and support conditions) and the necessity of higher-order model for the analysis of laminated structure have been highlighted by solving wide variety of static and vibration examples.
Aluminum matrix composites reinforced with micro- and nano-sized Al2O3 particles provide desirable characteristics for high-performance applications in aerospace, automobile, and military industries, because of their improved physical and mechanical properties. Selection of the best combination of ultimate strength and formability properties of the composites is a multiple attribute decision making problem where some criteria must be considered. In this study, A356/Al2O3 composites were prepared with different conditions such as the fabrication method, size, and weight fraction of reinforcement. These alternatives were ranked by analytic hierarchy process method. Analytic hierarchy process results revealed that the composite with 2 wt% nano-Al2O3 fabricated by compo-casting method was the preferred composite material.
An experimental study has been carried out to investigate the mechanical and tribological characteristics of chopped carbon fiber (CCF) reinforced epoxy composites filled with nano-Al2O3 particulates, as a function of fiber and filler contents. The experiments were conducted using a pin-on-disc wear test apparatus under dry sliding conditions. The coefficient of friction and specific wear rate of these composites was determined as a function of applied normal load, sliding velocity, sliding distance, and reinforcement content. The tensile, flexural, and compression strengths of ortho cresol novalac epoxy and chopped carbon fiber (OCNE/CCF) filled composites are found to be within the ranges of 48–58.54 MPa, 115–156.56 MPa, and 48–61.15 MPa. Whereas the tensile, flexural, and compression strengths of OCNE/CCF/Al2O3-filled composites are found to be within the ranges of 96–110 MPa, 176–204.66 MPa, and 72–85.65 MPa, respectively. It has been observed that the coefficient of friction decreases and specific wear rate increases with increase in the applied normal loads. Further increases in the fiber (6 wt%) and particle (3 wt%) contents in the epoxy matrix resulted in a decrease of both the mechanical and tribological properties, but remains above that of the CCF reinforced epoxy composites. The worn surfaces of composites were examined with scanning electron microscopy equipped with energy dispersion X-ray analyzer and X-ray diffraction analysis technique to investigate the wear mechanisms.
The behavior of woven glass fiber reinforced plastic laminates containing interacting circular holes off the loading axis under cyclic loads in tension–tension has been investigated with a fiber volume fraction of 0.65. The tests were conducted in load control mode from 80% of the ultimate tensile strength to the threshhold to draw the stress–life curves. For the unnotched, central holed, and off-center interacting holed specimens, the damage pattern and its evolution are extensively discussed. The damage development in interacting holed specimens occurs in four different stages namely matrix cracking, edge delamination, matrix splitting, and final fracture. The damage pattern depends on the location of the interacting circular hole and stress level. The sectioned parts of laminates fatigued at different stress levels were examined on scanning electron microscope for the damage evaluation.
A considerable residual stress distribution can be produced while bending of parts. This stress distribution depends on material behavior. In this article, residual stress distribution has been determined through the thickness in beam bending. For three different models of elastic–plastic behavior, the stress distribution and maximum residual stress are derived analytically. The residual stress is compared for three different bending radii as a case study. Also, finite element analysis has been carried out for two material properties. The results show that material behavior has little effect on stress distribution for large value of bending radius. As the bending radius decreases, difference of stress distribution increases rapidly among three plastic behaviors. Comparing the results of finite element and analytical stress distribution shows good accuracy for suggested formulations.
Ceramics reinforced aluminum metal matrix composites are mostly used in automobile, aerospace, and its related industries because of its superior mechanical and tribological properties. In the present work, the drilling studies of LM25 aluminum-based composite is selected to carry out the experiments. Novel industrial waste red mud particles are used as the reinforcement material, which can reduce the environmental hazards and the problem of disposing. The effect of three input factors such as speed, feed, and point angle over the output response such as surface roughness, vibration, and power consumption are studied using L27 orthogonal array. The optimal factor settings for each output performance are determined by employing the Taguchi method. Further, the analysis of variance is also performed for each parameter to know the significant contribution. However, in order to minimize the responses simultaneously, multi-objective optimization by ratio analysis based entropy method is adopted and the optimum levels of the drilling process are found. When the optimum parametric setting is used, the surface roughness is reduced by 13.63%, power consumption by 9.1%, and vibration by 15.14%.
This paper presents the experimental investigation on the electro-discharge machining of aluminum alloy 6061 reinforced with SiC particles using sintered Cu–W electrode. Experiments have been designed as per central composite rotatable design, using response surface methodology. Machining characteristics such as material removal rate (MRR), electrode wear ratio (EWR), and surface roughness (SR) have been investigated under the influence of four electrical process parameters; namely peak current, pulse on time, pulse off time, and gap voltage. The process parameters have been optimized to obtain optimal combination of MRR, EWR, and SR. Further, the influence of sintered Cu–W electrode on surface characteristics has been analyzed with scanning electron microscopy, energy dispersive spectroscopy, and Vicker microhardness tests. The results revealed that all the process parameters significantly affect MRR, EWR, and SR. The machined surface properties are modified as a result of material transfer from the electrode. The recast layer thickness is increased at higher setting of electrical parameters. The hardness across the machined surface is also increased by the use of sintered Cu–W electrode.
This paper reports the development of unidirectional natural fiber-reinforced thermoset composites and their mechanical properties. A thermoset epoxy resin was used as the matrix polymer, with abaca fiber as the reinforcing phase. The tensile strength and Young’s modulus of the proposed thermoset composites respectively reached maxima of 520 MPa and 17 GPa at the fiber volume fraction of 79%. Such high strength and high modulus apparently derived from good permeability of resin into abaca fiber stocks and also from the acceptable stress transfer between the fiber and matrix. The experimental tensile strength was compared with the theoretical prediction derived from the Curtin model in which the stochastic fiber fracture is considered. It is apparent that the tensile strength of the abaca fiber-reinforced thermoset composites was slightly lower than that estimated using the Curtin model, and that this deviation derives partially from insufficient stress transfer between the fiber and matrix.
The continuation from rapid prototyping into rapid tooling technologies allows speedy fabrication of sacrificial patterns for investment casting process. Direct expendable pattern fabrication with intricate features using rapid prototyping techniques significantly reduces the fabrication cost when associated with single- or low-volume production. During investment casting process, rapid prototyping patterns are subjected to high melting temperatures, high viscosities, and high thermal stress such as dewaxing and shell mold cracking. Furthermore, ceramic shell may cause crack during melting and burning out of the patterns and also incomplete collapsibility. Although rapid prototyping process can build parts with high stiffness rapidly, the part surface suffered a staircase effect and shrinkage during investment casting process solidification. This paper presents a direct approach of multijet modeling and fused deposition modeling on acrylate- and acrylonitrile–butadiene–styrene-based materials to be used as expendable patterns for the investment casting process. Thermal analyses were conducted on the rapid prototyping materials that exhibit mass loss and expansion. Quality assessment and benchmarking were performed between the rapid prototyping and the metal part on accuracy, surface roughness, and part built time. It was found that both the materials have dimensional deviation when employed in investment casting process and acrylate patterns have better surface roughness as compared to acrylonitrile–butadiene–styrene patterns. Additionally, multijet modeling recorded a significantly shorter lead time when more than a single part can be produced during the rapid prototyping process. It was observed that the shell mold after burnout experiences cracking. Results also showed that acrylate-based materials decomposed above 500℃, meanwhile acrylonitrile–butadiene–styrene was above 600℃. Acrylate material had a coefficient of thermal expansion and linear dimensional deviation as compared with acrylonitrile–butadiene–styrene. No ash was observed in the ceramic molds when the part burnout temperatures are above 500℃ acrylate material and 600℃ for acrylonitrile–butadiene–styrene.
The nondestructive test method (eddy current) was employed to study the effect of different heat treatment cycles (normalizing, annealing, quenching, and tempering) on chromium–vanadium (CrV) spring steel. The calibration of eddy current setup was carried out as per ASTM E566 and frequency optimization for the evaluation of heat treatment was carried out in absolute mode using shielded eddy current testing core probe. The eddy current signatures successfully distinguished the effect of different heat treatments cycles and variation in hardness for CrV samples. Scanning electron microscopy images confirmed the different microstructures as predicted by the eddy current testing.
Leak before break is a fail–safe design concept for application in pressure vessels and piping of power and process plants. A quantitative maximum allowable flaw size is required to establish to set acceptance/rejection limit to predict whether the specific cracked pipe will leak or break. A new modification and its boundary based on Modified Two Parameter Fracture Criterion is capable of separating the leak and break cases distinctly in order to predict the behavior of cracked cylinders, pipelines and pressure vessels in advance for taking necessary precautions by the plant operator and also very much handy for the designers. For the given operating pressure under the observed crack dimensions, whether the crack will leak or break can be assessed from the boundary generated for the material concerned using Modified Two Parameter fracture assessment procedure.
Design optimization of defense hole systems placed near the main circular cutout of composite laminated plates subject to biaxial loading is performed in this study. For that purpose, a numerical framework based on finite element models validated experimentally via RGB-photoelasticity and by reproducing selected cases available in literature is developed. Redesign optimization technique is utilized to reach the optimum geometric design parameters of the defense hole system, i.e., size and location. Parametric study for fiber orientation, biaxial loading ratio, stiffness ratio and stacking sequence is conducted as well. Stress concentration near circular cutouts can be reduced by 24.5%, 25.5%, 29.1%, 31.7% and 20.6% for values of the loading ratio equal to, respectively, 0, 0.25, 0.50, 0.75 and 1. Such significant reductions are obtained by introducing four elliptical defense holes along the principal stress direction lined up with fibers.
The paper reports on investigations into the erosion, microstructural features, and material removal mechanisms of AISI H13 core boxes eroded by two types of core sand (silica and chromite). Different heat treatment operations are carried out, namely martempering, carbonitriding, quenching, and tempering, in order to vary hardness, microstructure, and surface morphology. Scanning electron microscopy inspections show that erosion is not only a function of surface hardness of the target material but also of its microstructure. Erosion of martensitic microstructure, consisting of very fine carbides with a uniform martensitic substructure, is much less severe than erosion of a material characterized by dispersed coarse carbide. Hardness effects on the erosion process are discussed in terms of material removal modes.
DMR249A steel is indigenously developed high strength low alloy (HSLA) steel. The steel is being used for construction of Indian Aircraft Carrier and other new ships under construction at various ship yards in India. In order to enhance the depth of penetration (DOP) achievable in a single pass for gas tungsten arc welding (GTAW) process, activated fluxes were developed for the steel. The process is called activated flux gas tungsten arc welding (A-GTAW). Design of experiments (DOE) approach was employed using response surface methodology (RSM) and Taguchi technique to optimize the welding parameters for achieving maximum DOP in a single pass. Design matrix was generated using DOE techniques and bead on plate experiments were carried out to generate data for influence of welding process variables on DOP. The input variables considered were current, torch speed, and arc gap. The DOP was considered as response variable. The equations correlating DOP with the process parameters were developed for both the optimization techniques. The identified optimum process parameters were validated by carrying out bead on plate experiments. The RMS error of the predicted and measured DOP values for the validation experiments of the RSM (D-optimal) and Taguchi optimization technique was found to be 0.575 and 0.860, respectively. Thus, RSM (D-optimal) was observed to predict optimized welding process parameters for achieving maximum DOP with better accuracy during A-GTAW process.
In the present study, friction stir welding (FSW) and tungsten inert gas (TIG) techniques were used to join the dissimilar aluminum alloys of 5083-H12 and 6061-T6. The laboratory tests were designed using design of experiment (DOE) method. Variables for the FSW process were the rotational speed, traverse speed, shoulder diameter, and pin diameter. They changed in ranges of 700–2500 r/min, 25–400 mm/min, 10–14 mm, and 2–4 mm, respectively. In the case of TIG process, the variables were current intensity, traverse speed, and tilt angle. These parameters varied from 80 to 90 A, 200 to 400 mm/min, and 3° to 12°, respectively. The optimum amounts of parameters were obtained using response surface methodology (RSM). The RSM-based model was developed to predict ultimate tensile strength (UTS) of the welds produced. In FSW, the difference between predicted and measured UTS was about 1.28% and in TIG it was 1.78%. The good agreement between experimental and predicted results indicates the high accuracy of the developed model. Mechanical properties and also the microstructure of the welds were compared after optimizing both welding processes using RSM. The results showed that the welds produced by FSW indicated a considerably higher quality and also improved mechanical properties compared to TIG. Properties of the joints obtained by FSW in single-sided joints were more desirable. In the double-sided welds obtained by FSW these differences were of an even higher significance.
In the present work, microscale deformation behavior, plastic strain localization, and plastic instability of rheocast Al–Si–Mg (A356) alloy have been investigated using micromechanical approach. For this purpose, two-dimensional microscale models (representative volume elements) have been developed using actual microstructure of the cast samples made under three different process conditions. Microstructure of the above-mentioned alloy consists of two different phases, such as aluminum-rich primary phase and silicon-rich eutectic phase. In line with that, composite micromechanical models have been developed to analyze them within the finite element framework. Rheocasting has been performed using cooling slope with two different slope angles of 45° and 60°, and comparison has been made with the conventional cast samples of the alloy that has been cast directly from the superheated molten state. Different boundary conditions have been assumed to perform finite element based simulation, using a popular finite element solver ABAQUS, depending upon the position of representative volume elements on the cylindrical tensile specimen. Under uniaxial tensile loading, ductile failure mode is predicted in the form of plastic strain localization due to incompatible deformation between the phases. This indicates inhomogenity of microstructure that determines the damage initiation process within this material, as there is no damage or failure criterion specified during the finite element analysis. Grain size, shape, and orientation of the primary aluminum phase are found to play a vital role on deformation behavior and failure mode of the materials investigated in this study.
In the present investigation, the influence of tool pin profile and postweld heat treatment on microstructure, hardness, and static immersion corrosion behavior of AA7020-O Al plates joined by friction stir welding was investigated. Friction stir welding was conducted using two tools having different pin profiles, typically, a tool with tapered cylindrical pin and a tool with two flat-sided cylindrical pin. Postweld heat treatment was carried out using a solution heat treatment temperature of 540 ± 1℃ for 12 h followed by aging at 155 ± 1℃ for 6 h. Corrosion tests were carried out by immersing the welds in an aqueous solution containing NaCl and H2O2 for 6 h according to ASTM-G110. The results revealed that the two flat-sided cylindrical pin tool produces finer α-Al grains, at the center of dynamically recrystallized zones, than the tapered cylindrical pin tool. The postweld heat treatment slightly increases the size of the α-Al grains at the center of dynamically recrystallized zones. In the as-welded conditions, the friction stir welded regions exhibited lower hardness values than the base alloy. However, the regions friction stir welded using two flat-sided cylindrical pin tool showed relatively higher hardness values than those regions friction stir welded using the tapered cylindrical pin tool. The postweld heat treatment slightly increases the hardness of the welded regions to values that are still lower than the base alloy. Generally, the dynamically recrystallized zones are more susceptible to corrosion than the base alloy. In both AW and postweld heat treatment conditions, the thermomechanically affected zones showed the lowest corrosion resistance when compared with dynamically recrystallized zones and heat affected zone regions. In the as-welded conditions, regions friction stir welded using tapered cylindrical pin tool exhibited better corrosion resistance than those friction stir welded using two flat-sided cylindrical pin. The postweld heat treatment improves the corrosion resistance of the dynamically recrystallized zones friction stir welded using two flat-sided cylindrical pin tool.
Forming limit curve (FLC) is a suitable method for determining the metallic sheets formability. The purpose of the present research is to expose a simulation-based approach to predict the FLC in two-layer metallic sheets. In this paper, the formability of two-layer (AA3004-ST12) metallic sheets, with an aluminum inner layer (in contact with the punch) and a steel outer layer (in contact with the die) was numerically investigated. Two distinct criteria, including the acceleration (i.e. the second time derivatives) of thickness, and major strain extracted from the strain history information of finite element software, were applied to determine the commencement of local necking in FLCs. It shows that the localized necking starts when the acceleration of the thickness or major strain, is maximized. The published experimental results for AA3004/ST12 two-layer metallic sheets were employed in order to evaluate the simulation results. It is shown that the presented methods are noticeably aligned with the published experimental data. By the grace of present methods, the effects of some process parameters on the FLC have been investigated. It is shown that process parameters such as thickness and lay-up of each layer will have significant influences on FLC of two-layer metallic sheets.
This research work focuses on comparison of the weld geometry, distortion, microstructure and mechanical properties of thin SS 304 L sheets (0.8 mm thickness) welded using micro-plasma arc welding and tungsten inert gas welding process. Initial experiments were performed to identify suitable processing parameters for micro-plasma arc welding and tungsten inert gas welding processes. Microstructures of welds were analysed using scanning electron microscopy, X-ray diffraction and energy dispersive spectroscopy. The results indicate that the joint produced by micro-plasma arc welding exhibited higher tensile strength, higher ductility, smaller dendrite size and a narrow heat affected zone. Samples welded by micro-plasma arc welding process had lower distortion as compared to that welded by tungsten inert gas process. Micro-plasma arc welding was shown to be the suitable process for welding of thin 304 L sheets owing to its higher welding speed and better weld properties as compared to the tungsten inert gas welding process.
A judicious material constitutive model used as input to the numerical codes to denote elastic, plastic, and thermomechanical behavior under elevated temperatures and strain rates is essential to analyze and design a process. This work describes the formulation of different constitutive models, such as Johnson–Cook, Zerilli–Armstrong, Arrhenius, and Norton–Hoff models for high-strength aeronautic aluminum alloy AA7075-T6 under a wide range of deformation temperatures and strain rates. The adeptness of the formulated models is evaluated statistically by comparing the value of the correlation coefficient and average absolute error between experimental and predicted flow stress results, and numerically when simulating AA7075-T6 machining process. Though all the models show a reasonable degree of accuracy of fit, based on the average absolute error of the data and finite element predictions when simulating the AA7075-T6 machining process, Zerilli–Armstrong model can offer an accurate and precise estimate and is very close to the experimental results over the other models.
In this study, porous hydroxyapatite structures were produced by using urea particles of 600–850 µm size. Samples with two different urea composition (25 and 50 wt%) were prepared along with samples without any urea content by adding urea to commercially available hydroxyapatite in its as purchased and calcined states. The produced pellets were sintered at 1100 ℃ and 1200 ℃ for 2 h. Compression tests and microhardness measurements were conducted and changes in density values were examined in order to determine the effect of the calcination state of the prior hydroxyapatite powder, the sintering temperature and the amount of urea added. Also X-ray diffraction, Fourier transform infrared, and scanning electron microscopy analyses were conducted to determine the phase stability, functional groups, and pore morphology, respectively. Calcination is found to negatively affect the densification and sinterability of the produced samples, resulting in a decrease of compressive strength and microhardness. With the control of the urea content and sintering temperature uncalcined hydroxyapatite can successfully be used to tailor the density and mechanical properties of the final porous structures.
Microstructure and mechanical properties of microwave welded Inconel 718/ austenitic stainless steel (SS-316L) were investigated in this work. Principles of microwave hybrid heating were effectively applied for joining of Inconel 718/SS-316L using Inconel 718 powder as an interfacing layer between the candidate surfaces. Experiments were carried out in a thermally insulating box placed inside an industrial microwave applicator for a duration of 600 s. The microwave-induced dissimilar welds were characterized using X-ray diffraction, field emission scanning electron microscope, microhardness tester, and universal testing machine. The X-ray diffraction study of the fusion zone showed the presence of various carbides and intermetallics. Microstructural study revealed metallurgical bonding between the two faying surfaces with no sign of interfacial cracking. The elemental analysis of the welded zone confirms dilution of Inconel 718 powder across the joint interface during microwave hybrid heating. The average microhardness on the joint interface was observed to be 230 ± 5 HV; the average porosity was monitored to be 0.94%. The average ultimate tensile strength of the microwave welds was monitored as 517.5 MPa with 18.18% elongation. The fractography study reveals a mixed mode of failure of the joints during tensile testing.
Due to numerous difficulties associated with the experimental investigation of the single-walled carbon nanotubes (SWNTs), computational modelling is considered to be a powerful alternative in order to determine their mechanical properties. In this study, a novel three-dimensional finite element model incorporating a beam element with circular cross section is developed based on equivalent-continuum mechanics approach. The beam elements are used as the replacement of C–C chemical bonds in modelling SWNTs. Finite element models are generated for a range of SWNTs and employed for the evaluation of effects of diameter and chirality on the mechanical properties including Young’s modulus, shear modulus, shear strain and Poisson’s ratio of SWNTs. The results of this study are in good agreement with those reported in literature.
Titanium and its alloys are known as one of the most significant metallic materials used in the orthopedic and dental implants due to their excellent mechanical properties, corrosion resistance, and biocompatibility. One of the main issues in dental implant is the fabrication of the biomaterials that have early and sufficiently strong bonding with the surrounding bone. In the present study, porous Ti6Al4V scaffolds were synthesized using the powder metallurgy with various amounts of magnesium. The specimens were sintered at 950 ℃, close to magnesium vaporization point, because of the remaining magnesium in the scaffolds. The microstructure and mechanical properties of the specimens were investigated. Electrochemical characterization was carried out to indicate the effect of porosity on corrosion resistance. This investigation showed that the porous Ti6Al4V scaffolds containing 5–10 volume percent of magnesium with 28–31% porosity as a semi-degradable implant could be an advanced alternative for clinical application under load-bearing conditions such as dental implants which require two factors of strength and osteointegration.
Wettable nonwoven topsheets are traditionally spunbond polypropylene nonwoven fabrics. The fluid handling performance of hydroentangled greige cotton nonwovens was studied to determine their suitability for topsheet applications based upon analysis of fluid rewet, strikethrough, and acquisition properties; and the relative contributions of nonwoven cotton’s cellulosic and wax components to hydrophobic and hydrophilic fluid transport properties are addressed. It was observed that mechanically cleaned greige cotton nonwovens exhibit certain fluid handling properties that are similar to polypropylene spunbond-meltblown topsheets, partly as a result of the residual wax content. Subsequently, the surface polarity, swelling, and moisture uptake of 100% greige cotton and 50:50 blends of greige cotton and polypropylene hydroentangled nonwovens were studied in comparison with the performance of a commercially available 100% polypropylene spunbond-meltblown topsheets. The surface polarity, swelling, and wettability values obtained from electrokinetic and water contact angle analysis were found to be in agreement with the hydrophobic polypropylene topsheets. Additionally, comfort assessment was undertaken based upon fabric handle profiles using the Leeds University Fabric Handle Evaluation System, which is an objective evaluation based on the quantification of fabric buckling deformations. Of the fabrics studied in this work, 50:50 greige cotton/polypropylene hydroentangled fabrics were the softest as determined by the Leeds University Fabric Handle Evaluation System and exhibited fluid handling properties consistent with the requirements of commercial topsheets.
The time has come for natural fibres to stand as potent substitutes for synthetic fibres in various industrial applications. Recently, jute fibre is being used as reinforcement material in the development of reinforced plastics for various engineering products. The production cycle of a composite product often necessitates certain degree of machining operations. Drilling is one of the most widely practised machining operation for making holes in composite laminates. Hole making is imperative to ascertain the assembly of intricate composite products. The literature available indicate that not much research work has been reported on the machining behaviour of jute fibre-reinforced polypropylene composites. Hence, in the present experimental endeavour, drilling of woven jute fabric-reinforced polypropylene composite has been performed. The effect of operating variables on thrust force and torque signals was investigated. Drilling-induced damage in the developed composite was quantified using stereo microscope. The experimental values indicate close relationship between the tool geometries and the delamination factor. SEM analysis was also conducted to understand the drilling behaviour and surface morphology of the drilled holes. Among the solid drills compared, parabolic drill reveals better cutting behaviour in terms of lower drilling forces and better quality of holes. This may be attributed to the better tool-work piece interaction in case of parabolic drill point geometry.
To improve the simulation accuracy in sheet metal forming, an improved equivalent drawbead restraining force model is proposed considering the offset of the neutral layer and Bauschinger effect. It is validated with Nine's experimental data. BP neural network is optimized by the regularization and pruning theory to decrease neural network redundancy. The weights and threshold values of BP network are optimized by dynamic Particle Swarm Optimization (PSO) algorithm to reduce the possibility of local values. The surrogate mapping model of input–output variables is obtained from the improved PSO-BP model. The fender from NUMISHEET'93 is selected as case study. The main factors are sampled making use of Latin hypercube. The Latin hypercube sampling is optimized by simulated annealing algorithm. Based on the improved PSO-BP neural network, the metamodel between drawbead forces and forming objectives is established. Based on the multi-objective PSO optimization method, the mapping model is optimized to obtain the optimum drawbead restraining forces. The inverse model of drawbead is established based on the proposed drawbead force model to obtain its geometric parameters. The actual drawbeads based on the inversed parameters are simulated to verify the feasibility of the method. The results show that proposed method can significantly improve the forming quality.
This paper extends recent developments in the mechanical joining of metallic tubes by their ends at room temperature to polymer tubes. The presentation describes the experimental and finite element research work with commercial PVC tubes that was performed to characterize the deformation mechanics of the process and to identify the workability limits as a function of the major operating parameters. Experiments with water tightness destructive tests demonstrate the capability of the mechanical joining process to produce tight, structurally sound joints that are able of withstanding internal pressures above the maximum operating pressure of the individual PVC tubes, while eliminating extra components and facilitating the ease of installation.
Gas metal arc welding (GMAW) is extensively used for joining of different graded steels as well as aluminium and other nonferrous materials. GMAW offers clean welding with low defects without using flux and suitable for different positional welding. In the present work, a fabricated automatic movement setup is used for GMAW to study the influences of four different process parameters during joining of austenitic stainless steel AISI 316 using AISI 304 (ER304) filler wire. With this setup, welding is carried out maintaining a constant contact tube-to-workpiece (CTW) distance and uniform heat input. Experimental results and subsequent analysis show that the toughness is most significantly influenced by voltage followed by welding speed, gas flow rate, and current. Toughness reduces with the increase in shielding gas flow rate and welding speed as austenite and traces of retained delta ferrite may be present due to high solidification rate. Metallurgical observations by X-ray diffraction (XRD) and scanning electron microscopy indicate that solidification mode is mainly characterized by formation of fully austenite or austenite and ferrite at cell and dendritic boundaries. XRD results revealed that higher toughness is observed due to minimum formation of carbides.
The purpose of this paper is to investigate the structural behavior of aluminum alloys used in the aerospace industry when exposed to conditions similar to those of an accident scenario, such as a fuel fire. This study focuses on the role that the aluminum oxide layer plays in the deformation and the strength of the alloy above melting temperature. To replicate some of the thermal and atmospheric conditions that the alloys might experience in an accident scenario, aluminum rod specimens were subjected to temperatures near to or above their melting temperature in air, nitrogen, and vacuum environments. The characteristics of their deformation, such as geometry and rate of deformation, were observed. Tests were conducted by suspending aluminum rods vertically from an enclosure. This type of experiment was performed in two different environments: air and nitrogen. The change in environments allowed the effects of the oxide layer on the material strength to be analyzed by inhibiting the growth of the oxide layer. Observations were reported from imaging taken during the experiment showing creep behavior of aluminum alloys at elevated temperatures and time to failure. In addition, an example of tensile load–displacement data obtained in air and vacuum was reported to understand the effect of oxide layer on aluminum deformation and strength.
In the present work, optimum A-TIG welding process parameters have been determined using the design of experiments approach to achieve the desired depth of penetration (DOP) during welding of duplex stainless steel (DSS) alloy 2205. The design matrix for welding experiments was generated using the central composite design of response surface methodology. Bead-on-plate welds were made on 10 mm thick DSS alloy 2205 plates to generate data and to study the influence of process parameters on DOP. ANOVA analysis was carried out to determine the significance of the process parameters. Current was found to be a significant parameter influencing DOP. A second-order response surface model was developed to predict the response for the set of given input process parameters. Then, numerical and graphical optimization was performed to obtain the maximum DOP using desirability approach. Validation of the model showed good agreement between the predicted and actual values of DOP.
In this paper, springback of anisotropic sheet based on the modified form of the asymmetric non-quadratic yield function (YLD96) for plane stress conditions due to Barlat et al. (Yield function development for aluminium alloy sheets. J Mech Phys Solids 1997; 45: 1727–1763), suitable for describing mixed (isotropic and kinematic) hardening in aluminium alloy sheets under the Bauschinger Effect was compared with the results of tests. Simulation of uniaxial tensile and cyclic tests including both nonlinear isotropic and nonlinear kinematic hardening showed the necessity of including the Bauschinger effect in the constitutive equations at both small and large strains. Following the application to prediction of springback in draw bending of these alloys oriented in the rolling direction, draw-bending tests on AA2024-O and AA7075-O alloy sheets are described. The springback parameters of specimens with axes oriented at 45° and 90° to the rolling direction were measured and compared with prediction based on the modified form of the YLD96, which captured the hardening response at small and large strains when combined with the mixed hardening model, predicting springback in very good agreement with experimental results. The number of components of back stress used in this model depends on the nature of the nonlinear behaviour of the material. For alloys AA2024-O and AA7075-O, excellent agreement with experiments required the use of up to three nonlinear components of back stress. Prediction suggested values of friction consistent with published values and showed that friction inversely affected the radius of sidewall curl, but was not sensitive to lower and upper opening angle. This was consistent with the findings of Carden et al. (Measurement of springback. Int J Mech Sci 2002; 44: 79–101), although those authors also reported that very low friction may increase springback in their proposed draw-bending test. The results confirmed the efficacy of the yield surface model based on YLD96, modified to include nonlinear isotropic and nonlinear kinematic hardening, for predicting deformation subject to the Bauschinger effect.
A finite element method is developed and validated for the estimation of loss factors of a viscoelastically damped plate. Viscoelastic layer is used as constrained layer and is sandwiched between an aluminum base plate and a constraining layer. Frequency-dependent material properties are used for the viscoelastic material in the finite element model. The derived dynamic equations of motion are used to carry out harmonic analysis to determine the natural frequencies and loss factors of sandwich plate and validated with experimental results for cantilever boundary condition. The validated finite element model is then used to estimate the loss factors of sandwich plate with various boundary conditions and different thicknesses of constraining and constrained layer for a given base plate thickness. The results show that the loss factor is maximum for a constraining layer to sandwich plate thickness ratio of 0.40–0.45 and is independent of boundary condition. The loss factor increases with increase in thickness of the viscoelastic layer. The loss factor increases for higher mode for all boundary conditions.
In order to ensure good quality joints between aluminum sheets by resistance spot welding, a new approach involving the addition of metal powder to the faying surfaces before resistance heating is proposed. Three different metal powders (pure aluminum and two powders corresponding to the alloys AA2024 and AA7075) are investigated for the resistance spot welding of AA1050 aluminum sheets of three different thicknesses. Microstructural and mechanical analysis demonstrates that significant improvement in weld bead morphology and strength are obtained with the addition of metal powder. The improvement obtained is shown to be due to the development of a secondary bond in the joint beside the weld nugget increasing the total weld area. The application of powder additive is especially feasible, when using welding machines with insufficient current capacity for producing the required nugget size. In such cases the best results are obtained with pure aluminum powder.
In this study, the micro-droplet debonding test for three kinds of different single fiber composites (CCF/epoxy resin-128, CCF/epoxy resin-5228, and CCF/ bismaleimide resin-5428) is carried out. Then the corresponding numerical model for the test is established in the general finite element software ABAQUS and the process of the elastic load transferring in the test is simulated. Based on the numerical results, the reasonable critical debonding load "F" in the test is analyzed and is extracted from the scattered experimental datum. And it is used to combine with the numerical simulation for the "interphase" debonding process in the test. So the strength parameters of the "cohesive element" in the numerical are analyzed and determined. It turned out that in the numerical model for the CCF/Bismaleimide5428 single fiber composite, the strength parameter of the "cohesive element" is much higher (they are 130 MPa). It is demonstrated that the strength of the "interphase" in this single fiber composite is much stronger than that in the other two single fiber composites. These parameters can also be used to characterize the properties of "interphase" in composites.
Laser beam forming process being a non-contact process requires no hard tooling systems and presses. Hence, it is considered suitable for low-volume and high-variety production of sheet metal parts for different industrial applications. This paper reports on the experimental and finite element-based numerical investigation of the laser beam forming process. The experimental setup for the investigation includes an Nd: YAG laser with a maximum power of 4.4 kW and adjustable beam diameter. The L-27 Taguchi Orthogonal Array Design of Experiment was employed in this study in order to identify the variables that mostly influence the outcome of the experiment. The optimised process parameter window employed for the laser beam forming process was further classified into the minimum, medium and maximum parameter window settings. The finite element analysis was performed using the commercial package ANSYS to validate the experimental results. This investigation was able to validate the response related to deformation and identify the effect of the laser power on the bending angle for the mild steel sheets used in this study. The finite element models were parametrically developed using the ANSYS Parametric Design Language, the scripting language provided in ANSYS version 14.0. The maximum variation in the bending angle between the experiment and the finite element simulation was 9%, recorded at the maximum parameter setting during the laser beam forming process. The results showed that there was a strong correlation between the numerical and the experimental results.
An experimental study of void distributions for rotationally moulded polyethylene is presented. The effects of key variables such as maximum process temperature and nominal wall thickness (via powder mass) are studied. Analytical models and finite element mass diffusion models for the permeability of heterogeneous polymers with air voids are presented and comparatively assessed. The FE method allows modelling of realistic (measured) void distributions. A preliminary estimation method for void volume fraction and mean void radius is presented. This approach is based on hot plate measurements and is shown to give good correlation with the rotationally moulded material for different process temperatures. Key objectives of the present work are (i) to develop an understanding of the factors affecting gas permeability in rotationally moulded polymers and (ii) to develop experimental and computational methods to help design low permeability rotomoulded polymer liners.
This paper evaluates the effect of auxeticity on the extent of shear deformation in isotropic beams. It is herein shown that the ratio of maximum deflection by Timoshenko theory to the maximum deflection by the Euler–Bernoulli theory reduces as the Poisson’s ratio of the beam material becomes more negative. The obtained results suggest that the ratio of shear deformation to bending deformation is lower in auxetic beams than in conventional beams, and that the use of Euler–Bernoulli beam theory for quantifying the deflection in auxetic beams gives lesser deviation from the Timoshenko beam theory than in conventional beams. Specifically, the shear deformation becomes insignificant for square beams with Poisson’s ratio of –1. A set of design equations that allows the use of simpler Euler–Bernoulli beam theory instead of the Timoshenko beam theory for the considered cases are proposed herein to justify the use of the former theory on beam analysis on the basis of reduced shear deformation as the beam’s Poisson’s ratio becomes more negative. The findings obtained herein also suggest that in comparison with conventional beams (of equal Young’s modulus, load distributions, and boundary conditions) the lower shear deformation in auxetic beams translates into smaller transverse deflections and hence better dimensional stability.
A non-linear cohesive zone model is developed for predicting stress–strain behaviour of unnotched aluminium alloys. A uniform cohesive layer is added into the middle of a dogbone-type specimen. Mechanical properties of aluminium alloy 6082 are used as those of a cohesive layer; Voce equation is used for describing the softening behaviour of heat treated and non-heat treated plates. Damage state of a cohesive zone due to tensile loading is evaluated with the damage variable expressed as a function of strain. Predicted engineering stress–strain curves are directly compared with experimental ones. Results show that a proposed model provides the prediction of stress–strain behaviour of aluminium alloys.
The effect of heat treatment on the axial crushing behavior of thin-walled aluminum 6061 alloy tubes is studied in this work. For this purpose, thin-walled grooved specimens were subjected to different aging heat treatments to obtain different work hardening behaviors. Afterward, quasi-static axial compression tests were achieved to evaluate the crushing behavior. Additionally, a finite element method simulation was employed to determine the distributions of stress, strain, and imposed damage during axial compression. Results show that the optimum energy absorption characteristics can be obtained using moderated strain hardening exponent, "n". Low strain hardening exponent results in the fracture of tube during axial compression while high strain hardening exponent causes lowered absorbed energy. On comparing the results of experiments and finite element method simulations, the fracture of tube during axial compression can be predicted using a simple fracture criterion.
Resin infusion process with/without the application of external pressure was employed for fabrication of unidirectional carbon fiber reinforced plastic composites. The prepared samples were tested under compression loads. Three kinds of fracture modes, viz., in-plane shear, complex fracture and through-thickness shear fractures were noticed. It was observed that samples fabricated with application of pressure exhibited in-plane and complex fracture modes whereas other samples displayed through-thickness fracture. Detailed fractographic analysis suggested that in-plane and through-thickness shear fractures resulted due to microbuckling of individual fibers; on the other hand, complex failure is governed by longitudinal splitting followed by microbuckling. Microbuckling directions for both in-plane and through-thickness shear fractures were established. These and other microstructral characterization results were analyzed and an effort was made to identify the reasons for variations in fracture modes and resulting compression properties.
This paper presents the first investigation on square hole-flanging produced by single point incremental forming. The aim and objective is to provide readers with a broad understanding on the deformation mechanics of the process that will enable them to understand plastic flow resulting from the interaction between the tool and the blank, to identify the influence of the pre-cut geometry in the overall formability, and to characterize the physics of failure. The methodology comprises the mechanical characterization of the material, the use of circle grid analysis, and the fabrication of square flanges with round corners by multistage single point incremental forming using blanks with different pre-cut hole geometries. The investigation is performed in aluminium AA1050-H111 and the overall results widens and enhances current research work in hole-flanging of cylindrical parts by giving the first contribution towards the understanding of plastic flow and failure in hole-flanging of square parts produced by single point incremental forming.
This review outlines some of the issues which have to be addressed when selecting an adhesive for a particular structural adhesive bonding application. The designer may find that a number of adhesives provide the required load bearing properties and the selection may require a more detailed consideration of the processes involved in the fabrication of the joint, the temperature over which it is to work and the environment in which it will have to operate. The article attempts to provide the reader with an insight into the effects of factors such as time and temperature used in the cure process, details of the components in the mixture and the effects of various additives on the physical properties of the adhesives which are created. The performance of an adhesive may vary with time as a consequence of stress-induced changes which are triggered by thermal effects or by hygrothermal factors. The review considers joints created using metal substrates and carbon fibre composites. The performance and durability of an adhesive bond is critically dependent on the stability of the interface between the adhesive and adherend and is sensitive to the pre-treatment processes used in the creation of the bond. The review outlines how broadband dielectric measurements can be used to non-destructively monitor the cure of adhesive bonds and the processes involved in ageing of joint. The dielectric method gives an insight into the fundamental processes which are giving rise to the changes in the mechanical properties of the joint as they age.
Functionally graded joints with an adhesive functionally modified by induction heating confer a more uniform stress distribution along the overlap and reduce the stress concentrations located at the ends of the overlap. The adhesive stiffness varies gradually along the overlap, being maximum in the middle and minimum at the ends of the overlap. This work studies the effect of post-curing on functionally graded joints obtained by induction heating. The performance of functionally graded joints, when submitted to different post-cure temperatures, was experimentally tested. Three different post-curing conditions were considered, with temperatures above and below the glass transition temperature of the fully cured network, Tg . The functionally graded joints (with and without post-cure) were compared with joints cured isothermally (with and without post-cure). The cure temperature values applied to the ends and to the middle of the graded joint are the same temperatures used to cure the isothermally cured joints. Analytical modelling was used to predict the failure load and to assess the effectiveness of the graded joint concept. The functionally graded joints subjected to post-cure at low temperatures (below Tg ) show a slight decrease of the strength and the joints cured isothermally show a slight increase of the strength. With increase of the post-cure temperature (above Tg ) the functionally graded joints exhibit strength similar to that of the joints cured isothermally. However, even for the highest post-cure temperatures, the functionally graded joints have a slightly higher strength.
A material’s inherent ability of strain distribution decides forming limits and affects the overall formability. In the present work, aero space grade titanium alloy – Titan 31 developed by MIDHANI India is selected. The material is hot rolled under alpha–beta-rolling process and heat treated at different temperatures and subjected to various cooling rates in the alpha plus beta regime to obtain a fine equiaxed alpha–beta microstructure that ensures high formability . Taguchi’s design of experiments approach is used to optimize the processing parameters (temperature, crosshead speed and angle-to-rolling direction specimen tested) to maximize formability depending on intrinsic material properties. Percentage contributions of these parameters towards maximizing the formability are also determined using analysis of variance. The optimal combination of parameters is evaluated as a temperature of 998 K, a crosshead speed of 1.25 x 10–5 m/sec and an angle of testing the specimen from rolling direction 45°, among all the parameters selected in the study.
In this study, indentation of circular metal tubes during lateral compression process between a V-shape indenter and a rigid platen is investigated by the experimental and theoretical methods. A new analytical model of plastic deformation in the circular metal tubes during the process is introduced and the theoretical analysis is performed based on the energy method and several relations are derived to predict the average lateral load and absorbed energy by the tubes as functions of lateral displacement, geometrical characteristics, and material properties of the tube. Also, to verify the theoretical analysis, some lateral compression tests were performed on circular metal tubes and the results were compared with the corresponding theoretical predictions. The comparison shows a good agreement between the theoretical predictions and experimental results and so, it confirms general form of the present theoretical formula. Also, effects of each geometrical dimension and material properties of the tubes on the average lateral load are investigated using the experimental measurements and the theoretical predictions.
Life cycle assessment methodology was applied as a tool to evaluate the real environmental benefit of using recycled waste tyres in mixture with virgin rubber. Styrene–isoprene–styrene rubber was mixed with different amounts of ground tyre rubber and vulcanised. Thermomechanical analysis (i.e. differential scanning calorimetry and thermogravimetric analysis) and dynamic mechanical thermal analysis were carried out in order to evaluate the compatibility of the rubber mixture and the chemical–physical properties of the vulcanised products. Experimental analysis results show that the addition of ground tyre rubber up to 50 phr does not sensibly affect the vulcanisation reaction, the wet skid resistance and the rolling resistance. Life cycle assessment results show that the main environmental impacts of the ground tyre rubber are associated to the use of virgin rubber (47.1%) and carbon black (34.3%) while the tyre grinding process contributes only for 4%. Because ground tyre rubber contains carbon black in its formulation, the substitution of virgin rubber with ground tyre rubber has double environmental benefits: to reduce the need of both amounts of virgin rubber and fresh carbon black in the new formulation.
Due to the rise of structural multi-material concepts in automotive and aerospace industries the role of adhesive bonding is becoming more important in the joining process. In contrast to joining technologies like welding or riveting, an electrical separation of the material by an insulating adhesive layer is given. This might be a problem if humans or electronic devices need to be protected against static discharge. This study investigates the effect of the alignment of non-magnetic spherical carbon black particles by magnetic forces enabled by adding secondary magnetic-sensitive fillers. To achieve this, an epoxy resin filled with carbon black and a small concentration of metal-based particles is used. The metal-based particles are aligned by magnetic forces provided by an external source. During the migration of the metal particles through the viscous epoxy adhesive, the carbon black particles are attached by adhesive forces. It is shown that this effect provides the alignment of non-magnetic carbon black particles, which results in an increased conductivity in carbon black filled epoxy resins.
In this paper, a comprehensive model of a piezoelectric laminated micro-switch subjected to electrostatic excitation, which accounts for the nonlinearities due to inertia, curvature, and electrostatic forces, is presented. Dynamic equations of this model is derived by the Lagrange method and solved by the Galerkin method using five modes. The laminated micro-switch is assumed as an elastic Euler–Bernoulli beam, and the piezoelectric material is bonded onto a portion of it. The electrostatic actuation results are compared with other existing experimental results. Whereas the major drawback of electrostatically actuated micro-switches is the high driving voltage, using the piezoelectric materials in these systems can provide less driving voltage. The effect of variation in the length, thickness, and applying voltage of the piezoelectric materials on mechanical characterizations is discussed. The aim of this work is design and control of a micro-switch using three different methods: the softening effect due to electrostatic actuation, the hardening effect due to piezoelectric materials, and varying the length and thickness of the piezoelectric materials. Also, this model can be used to design an actuator-sensor smart micro device.
This study elucidates how annealing temperature affects the mechanical properties and sensitization of 5083-H116 aluminum alloys. Nitric Acid Mass Loss Test was conducted to investigate the sensitization behavior of the annealed specimens. The results indicated that the mechanical properties were more sensitive to the annealing temperature than to the annealing time. The mechanical properties of the alloys became rapidly worse upon annealing between 250 and 350 °C. 5083-H116 aluminum alloy became sensitized and susceptible to intergranular corrosion at an annealing temperature of 175 °C for 48 h. The distribution and shapes of β-phase particles markedly affected the sensitization. Exposing at the temperatures of 230–250 °C for 10–30 min could effectively improve the sensitization of the 5083-H116 alloys.
The effects of sprue base size and design on flow pattern during aluminum gravity casting have been investigated by employing different sprue base sizes and using computational fluid dynamics. Calculations were carried out using SUTCAST simulation software based on solving Navier–Stokes equation and tracing the free surface using SOLA-volume of fluid algorithm. Flow pattern was analyzed with focus on streamlines and velocity distribution in sprue base, runner and ingate. Increasing well size produced a vortex flow at the bottom of sprue base, which increased the surface velocity of liquid metal in runner. Using a rather big sprue well could eliminate vena contracta but ingate velocity was observed to be independent of well size. It is assumed that ingate velocity may be more influenced by other casting considerations. Using a curved sprue base could remove vortex flow at the bottom of sprue while keeping a nearly full contact between liquid metal and runner wall.
In this research work, short glass fiber has been used to fabricate polyester-based homogeneous composites and their functionally graded material. Vertical centrifugal casting technique and simple mechanical stirring is used for fabricating functionally graded materials and homogeneous composites, respectytively. Wear tests are conducted over a range of sliding velocities (1.57–3.66 m/s), normal load (10–30 N), fiber contents (0–6 wt%), and sliding distances (1–3 km). Friction and wear characteristics of developed materials are successfully analyzed using Taguchi design of experiment scheme and analysis of variance (ANOVA). Artificial neural network approach is also applied to the friction and wear data for subsequent validation. Out of all samples fabricated it is found that 6 wt% short glass fiber polyester-based functionally graded materials exhibit lowest specific wear rate. Additions of short glass fiber in polyester-based functionally graded materials have an incisive effect on tensile and flexural strength in comparison to homogeneous composites. The morphology of worn composite specimens has been examined by scanning electron microscopy to understand about dominant wear mechanisms.
This study carries out the thermal residual stress analyses of functionally graded clamped hollow circular plates for in-plane constant inner and outer edge heat fluxes. The material properties of the functionally graded plates were assumed to vary with a power law along an in-plane direction not through the plate thickness direction. The transient heat conduction and Navier equations describing the two-dimensional thermoelastic problem were discretized using finite difference method, and the set of linear equations were solved using the pseudo singular value method. In order to determine the effect of the plate material properties on the thermal deformation and stress states the circular plates were designed in the way that their material compositions can vary from a pure ceramic (C) outer edge to a pure metal (M) inner edge and vice versa, such as ceramic-to-metal or metal-to-ceramic circular plates. The compositional gradient and direction affected considerably both in-plane temperature levels and heat transfer period whereas similar temperature distributions existed. The displacement components exhibited similar symmetrical distributions and were at lower levels in the metal-rich compositions. The normal strain components had similar distributions to those of the displacement components and were critical around both the inner and outer edges. A metal-rich composition resulted in lower normal strain levels. The equivalent strain distributions were always critical around the heat flux edge and became highest for a ceramic-rich composition. The normal stress components and equivalent stresses were critical in the ceramic-rich regions and the equivalent stress exhibited a sudden increase near the pure ceramic-edge subjected to the heat flux. The lower stress levels were also observed for a metal-rich composition variation. The ceramic material, a good thermal insulator, makes a metal-to-ceramic and a ceramic-to-metal material system suitable for outer and inner edge heat fluxes, respectively in practice. The metal-rich material compositions (with n = 0.1 and 10.0) can prevent the local cracks in the ceramic-rich regions induced by high heat gradients.
In this study, elastic plastic fracture toughness parameters of laser-welded 6013 aluminium alloy are investigated. For this purpose, compact tension specimens used in the experimental study are modelled using the finite element software. In the analyses, crack tip opening displacement (5) and J-integral values are determined and crack tip opening displacement, 5 and J-integral resistance curves (R-curves) are generated. Crack tip opening displacement, 5 resistance curves are compared with those obtained from the experimental work, and J-resistance curves are compared with those obtained from formulation. Effect of weld strength undermatching on crack tip opening displacement, 5 and J-resistance curves is discussed. ph values obtained by the plastic hinge method are compared with the crack tip opening displacement, 5 values. Fracture toughness parameters obtained from the finite element analysis showed a good agreement with those obtained from the experimental work and formulation. It is observed that the resistance curves obtained using the crack tip opening displacement, 5 and J-integral characterize the resistance of the material against crack growth in a similar manner, and strength undermatching decreases the fracture resistance. The relationship between ph and crack tip opening displacement, 5 is nonlinear, and as crack tip opening displacement increases, crack tip opening displacement, 5 becomes larger than ph.
This study focuses on the processing, analysis and optimization of parameters for mechanical properties (flexural and tensile) of multiphase hybrid composite consisting of bi-axial glass and jute mats reinforced polyester composites. An attempt is made to identify the main factors that affect the responses. The seven factors considered were presence of silicon carbide, percentage of NaOH used for alkali treatment of jute fibers, oven curing time for composites, stacking sequence of jute and glass fibers mat, hardener percentage in 50 mL resin, oven temperature and mixing time. The test specimens were prepared and tested according to ASTM standards. Taguchi design was used for design of experiments and experimental results were analyzed using ANOVA. The results revealed that for flexural strength the significant factors were stacking sequence and silicon carbide with p-values of 0.002 and 0.005 for mean analysis, respectively. Stacking sequence, silicon carbide and hardener percentage in 50 mL resin were found as significant factors with p-values of 0.010, 0.014 and 0.017 for tensile strength, respectively. These responses were further optimized for 95% confidence level. Further confirmatory test were carried out with optimum level parameters and results obtained were compared with estimated S/N ratio, which were within ±5%.
In the present study, gears made of 21NiCrMo2 (AISI 8620) steel were subjected to heat treatments including carburizing, decarburizing, boriding and hardening. Carburizing, decarburizing and boriding were performed in a gaseous atmosphere, a salt bath consisting of 60% NaCl and 40% NaCO3, and a liquid medium containing borax and silicon carbide, respectively. Borocarburazing was carried out in two steps: carburizing and then boriding. Some specimens were treated to obtain different carbon concentrations and to observe the effect of carbon content on the boriding process. This process, consisting of carburizing followed by decarburizing and finally boriding, is named borodecarburizing. The microstructures and phase compositions of the diffusion layers were examined by means of X-ray diffractometry, scanning electron microscopy and optical microscopy. The microhardness profiles of these layers were studied by a Vickers indenter. The hardness value obtained by the borodecarburizing process is 10% higher than a borocarburized specimen’s hardness. One-phase iron boride zone (Fe2B) was observed in the layers. This phase is preferred due to its mechanical properties.
In this study, scaling effects on fiber metal laminates under tensile and three-point bending tests were investigated numerically and experimentally. The fiber metal laminate specimens were made of aluminum 1050 and unidirectional glass–epoxy. Two scaled sizes of specimens were prepared based on [ A1n, 0n / 90n ]s. Some specified mechanical properties of these samples were investigated and results showed that fiber metal laminates obey scaling law under quasi-static loading. Explicit finite element code LS-DYNA was utilized for numerical simulation. After validating numerical simulation with experiments, scaling law was studied numerically for four different sample sizes. Finite element analysis demonstrated that scaling law is valid for fiber metal laminates. In final part, hole size effect in FML specimen was investigated numerically.
The welding tool geometry plays a critical role in acquiring desired microstructures and the heat-affected zones, and consequently improving the strength of the joint in friction stir welding. In this study, a friction stir welding process with different tool pin and shoulder diameter was numerically modeled. A thermomechanically coupled, 3D FEM analysis was used to investigate the effect of tool pin and shoulder diameter on welding force, material flow, thermal, and strain distributions in AA5083 aluminum alloy. Then, an artificial neural network model was employed to model the correlation between the tool parameters (pin and shoulder diameter) and heat-affected zone, thermal, and strain value in the weld zone.
Polymers and their composites are one of the most advanced and adaptable engineering materials. The strength of any composite depends upon number of factors such as volume/weight fraction of reinforcement, L/D ratio of fibers, types of fibers, orientation angles, chemical treatment of reinforcement, and many others. The present work focuses on the analysis of mechanical properties (tensile, flexural, and impact) of synthetic and natural fiber (glass/jute)-reinforced polyester composites. An attempt is made to reduce the usage of synthetic glass fibers by incorporating natural jute fibers such that the resultant hybrid composite shows increased strength when compared with single reinforcements of glass or jute fibers. The test specimens were prepared and tested according to ASTM standards. Experimental results revealed that reinforcement of natural fibers up to some extent increases the mechanical properties and reduces the overall cost of fabrication of composites.
Conventional indentation tests do not provide an accurate estimation of viscoplastic material properties. In this work, a combined finite element analysis and optimization approach is developed for the determination of elastic–plastic and creep material properties using only a single indentation loading–unloading curve based on a two-layer viscoplasticity model. Utilizing the indentation loading–unloading curve obtained from a finite element-simulated experiment with a spherical and a conical indenter, a set of six key material properties (Young’s modulus, yield stress, work hardening exponent and three creep parameters) can be determined. Non-linear optimization algorithms are used with different sets of initial material properties, leading to good agreements with the numerically simulated target loading–unloading curves.
In this paper, the elasto-plastic pre- and post-buckling behavior of beams made of functionally graded materials subjected to mechanical loading is investigated. A continuum-based finite element formulation is developed to determine the major characteristics of buckling. The arc-length algorithm is employed to analyze the stability problem. A plane stress von Mises model with isotropic hardening is utilized for the elasto-plastic nonlinear analysis of the beam. Basic idea in geometric and material nonlinear analysis of functionally graded material beams is to use the plasticity capacity of metal phase as a ductile material during loading. The influences of number of axial modes, material index, geometrical parameters and boundary conditions on the critical buckling point, pre- and post-buckling paths, plastic bifurcation point and stress distribution are fully studied. A good agreement between generated results and existing data in the literature is observed.
The mechanical behaviour of the commercial aluminium alloys EN AW-5182, EN AW-6016 and EN AW-7021 is investigated at temperatures ranging from 298 to 77 K and strain rates from 1.7 x 10–3 to 6.6 x 10–2 s–1. A device that allows testing at cryogenic temperatures is developed and demonstrated, where the specimens are subject to uniaxial tensile loads. The influence of a solution heat treatment for precipitation hardenable alloys is shown. The strain-hardening coefficient is determined and mapped in terms of the experimentally investigated uniform elongation. The experimental data of tested aluminium alloys are compared with EN AW-1050A-H14, which is used as a reference. The effect of the Portevin–LeChatelier effect on ductility and strength is discussed. The Ludwik relationship is adapted to describe materials showing a Portevin–LeChatelier effect.
In this study, the effect of milling time of processed powder coatings on the properties of 7Ch3 tool steel during plasma spray process was investigated. For this purpose, raw materials containing powders of titanium and carbon with stoichiometric ratio were milled and samples were taken in different time intervals. After phase investigations by X-ray diffraction, three milled samples as just mixed, activated and synthesized specimens were selected and coated on the substrate. The obtained results showed that titanium carbide can be successfully synthesized by mechanical alloying based on a gradual mechanism. Crystalline sizes of the synthesized carbide were found to be in nano-meter scale. Deposited coating leads to an increase in mechanical and wear properties of the substrate. The average sizes of coatings remained in nano-meter order too. Studies revealed that the sample which was coated by activated mixture had the best measured properties among the other specimens.
Various types of sandwich beams with viscoelastic cores are currently used in aerospace and automotive industries, indicating the need for simple methods describing the dynamics of these complex structures. In order to understand the effectiveness of the sandwich structures, the dynamics of bare beam with unconstrained and constrained viscoelastic layers are investigated in this study. The viscoelastic layer is bonded uniformly on the beam. The effects of distributed viscoelastic layer treatment on the loss factors are studied. From the experiments it is observed that beams with constrained viscoelastic layer provide higher loss factors than those with unconstrained layer. The dynamics of sandwich beams is modeled using Euler and Bernoulli beam theory. Frequency-dependent Young’s modulus and loss factors are considered in the model of viscoelastic material. The predicted Eigen frequencies obtained from the model are compared with the experimental results for two viscoelastic materials with aluminum base material. Frequency response functions are obtained from the finite element model and compared with experimental results for harmonic input. Reductions in vibration amplitudes for two viscoelastic materials (EAP-2 and EAP-43) are also compared. Based on the experimental results, it has been observed that the loss factors of EAP-43 are higher than that of EAP-2.
Heat generation due to dynamic loading has been a major concern for rubber component manufacturers over many years. In engineering design and applications, current practice is to monitor the component surface temperature in accelerated durability tests. However, a number of unexpected early failures from heat generation during accelerated durability tests for rubber components have been observed even the surface temperature was well-controlled. This situation has led to the development of heat generation prediction methodology. An integrated simulation and test programme has been set up on a case investigation on a solid rubber wheel. A drum test was carried out in the laboratory. Heat conductivity, convection and radiation are included in the simulation. Important rubber heat-transfer properties were measured in the laboratory and used for the simulation. A mixed Lagrangian/Eulerian method was successfully introduced in the simulation, due to the limitations of traditional FE methods, to reduce a great amount of cost and to make the simulation possible in practice. In this case, the degrees of freedom can be reduced by three times and about 170,000 rotations saved. The temperature change in real time-domain was recorded and failure regions located. The simulation results have shown that the temperature difference between the surface and inside in the solid rubber wheel can go about four-folds. The results have been compared with the laboratory test and shown very good agreement. From this investigation, it is shown that a proper calculation is needed when a product involves a large volume of the rubber during dynamic-loading tests, and the criterion to monitor the surface temperature alone is not always reliable and could lead to a potential unexpected failure. The principles and techniques can be employed for the prediction on heat generation in industries.
In this study, a new class of low cost hybrid composites consisting of glass-epoxy and filled with four different weight proportions (0 wt%, 10 wt%, 15 wt% and 20 wt%) of granite particulates (a solid waste generated from stone processing industries) are developed. Mechanical study reveals that hardness, tensile modulus and impact energy of these composites are improving with filler addition while a steady decline in tensile and flexural strength is observed. The erosion rates of these composites are evaluated at different impingement angles (30–90°), impact velocities (33–68 m/s) and erodent sizes (100–250 µm) following the erosion test experiments in an air jet type test rig. An optimal parameter setting is determined for minimum erosion rate and subsequently validated by conducting confirmation experiment as per Taguchi methodology. Erosion test results indicate that the incorporation of granite particulates results in improvement of erosion wear resistance of glass-epoxy composites. Different modes of material removal, wear craters and other qualitative attributes are examined by a scanning electron microscopy during erosion experiment of the samples.
The abrasive water jet is a 30-year old technology widely used to compete conventional machining capabilities. While it is mainly used for cutting applications, studies demonstrated its ability for milling, turning and micro-piercing. But as long as abrasive water jet issues are not clearly identified and analyzed, these processes can hardly be industrialized. This paper proposes an innovative methodology for studying abrasive water jet milling. Its main purpose is to consider the machined depth as an experimental factor and the feed rate as a product. A large-domain full-experimental-design on the pressure, the orifice diameter, abrasive mass flow rate, the milled depth and the feed rate on milling of aluminum 2024 T3 is presented. Finally, a mathematical model on the optimal abrasive mass flow rate and the milled depth are developed. The good correlation of these models within the large experimental domain suggests the pertinence of the proposed methodology.
In the present study, silicon carbide (SiC) filled cast aluminum (A356) alloy composites were fabricated using stir casting technique by varying SiC weight percentages from 0 wt.% to 25 wt.% at a range of 5 wt.%, respectively. The spherical shaped SiC particles of 60 µm size were uniformly mixed with the semi-solid alloy by mechanical stirrer. The physical and mechanical properties along with the fracture toughness of SiC filled A356 alloy composite were evaluated experimentally and compared with finite element analysis results for the validation purpose. It was found that the void content of A356 alloy composites varied from 1.01% to 2.69% and hardness from 21.25 HRB to 33 HRB with the increased SiC wt.% from 0% to 25%. The maximum experimental value of Young’s modulus and flexural strength at 25 wt.% SiC filled A356 alloy composite was found to be 150.55 MPa and 315.94 MPa, respectively. Impact energy of the SiC filled A356 alloy composite also increased from 3.92 J at 0 wt.% to 7.82 J at 25 wt.% SiC. It was established that the stress intensity factor for unfilled and SiC filled A356 alloy composites increases with the increased crack length for 0–25 wt.% SiC content. The tensile and flexural behavior of the composite is simulated by three-dimensional (3D) unit cell model using appropriate boundary condition in ANSYS. Finally, stress intensity factor for the crack propagation is determined using 2D simulation of single side edge cracked specimen in compact tension. The maximum percentage error for tensile strength and fracture toughness as calculated experimentally and by finite element method was found to be 5.74% and 7.69%, respectively, which is within the acceptable range.
This paper presents the results of micromechanical failure analyses of titanium metal matrix composite shafts, under cyclic torsional loading. Two different fibre orientations were used to investigate the failure mechanisms, namely +45° and ±45° fibre orientations. The fracture surfaces, after fatigue testing, were examined using a scanning electron microscope. Evidence was found of the existence of both ductile failure which occurred in the matrix material and brittle failure which occurred in the fibres. These modes of failure both played important roles in the overall shaft failure for a +45° fibre orientation. In the case of the ±45° fibre orientation, failure of the matrix, on the plane of the +45° fibres, was the main factor which influenced the fracture of the shaft.
In the present work, alumina (Al2O3)-filled cast aluminium alloy (A356) composites were fabricated using stir casting technique by varying Al2O3 contents (0, 5, 10, 15, 20 and 25 wt.%). The fabricated composites were studied for their physical, mechanical and fracture toughness behaviour experimentally, theoretically and compared with finite element analysis method to validate the experimental and theoretical results. The physical and mechanical results showed that the addition of alumina to A356 alloy led to the improvement in tensile strength, flexural strength, hardness and impact strength. The void content of A356 alloy composites increased from 1.01% to 3.30% from 0 to 25 wt.% Al2O3. Young’s modulus value varied from 80 GPa to 111.27 GPa at 0 to 25 wt.% Al2O3 filled A356 alloy composite. The maximum value of flexural strength as calculated experimentally is found to be 389 MPa at 25 wt.% Al2O3. A 3D simulation of the composite using the unit cell model was developed in ANSYS using appropriate boundary conditions for tensile and flexural strength. Stress intensity factor for the crack propagation is determined using 2D simulation of the single side edge cracked plate in compact tension. The mechanical properties determined in papers I and II are used for the optimization purpose. Technique for order preference by similarity to ideal solution was applied to rank the composites using criteria based on mechanical properties like tensile strength, Young’s modulus, flexural strength and stress intensity factor. As per the results obtained from the optimization, the composite with 25 wt.% SiC exhibits the optimal properties.
In this paper, butt joining of Al5083 to commercially pure copper by friction stir welding method has been investigated. The effect of welding parameters, rotational speed of the tool and tool offset on joint strength and microstructure have been studied experimentally. By examining different situations, joint strength was optimized in terms of rotational speed and offset. Results show that tool offset to the copper side reduces defects and increases the joint strength. Welded joint that was conducted at the rotation speed of 800 r/min, tool traverse speed of 40 mm min–1 and 1 mm offset to the copper side had the highest tensile strength, about 96% of the weak base metal strength. Microstructure in the stir zone had different morphology from that observed in the base metal. The analyses were performed in intermetallic compounds formed in this area. Al4Cu9 and Al2Cu, were the intermetallic compounds detected in stir zone.
Bicycle helmets are designed to reduce the acceleration/deceleration of the head during impacts. During an accident, the main parts of a helmet responsible for shock absorption are the energy-absorbing liner and the outer shell. In the present study, several geometrical structures of convex acrylonitrile butadiene styrene plastic shell, such as a truncated conical form and a semi-spherical form, were investigated for their energy-absorbing capacity. Moreover, several liner dimension parameters were also optimised. The energy was absorbed in these structures by a combination of folding and collapsing. The idea of a sandwich liner using the aforementioned structures was also constructed to analyse its advantages compared to their single structures. This study performs finite element analyses on helmet impact tests using LS-DYNA software based on the EN1078 standards. The purpose of the present study was to determine a structure of liner that reaches high effective protection and to design helmet models with single and dual liners. The final work in this study was performed to optimise the height cone of linear semi-sphere cones. This innovative design for a helmet liner demonstrated high energy-absorbing capabilities. Moreover, this helmet impact test model can serve as a valuable tool to assist future development of safety-helmet technologies.
Bending, buckling and free vibration behaviors of functionally graded (FG) carbon nanotube (CNT)-reinforced polymer composite beam under different non-uniform thermal loads have been analyzed using finite element method. Extended rule of mixture is used to obtain effective material property of the composite. Four different types of FG beam exposed to four different assumed one-dimensional temperature distributions along the length of the beam are analyzed. Parameters studies are carried out to investigate influences of the volume fraction of the carbon nanotube, functional grading and the nature of temperature variation on bending, buckling and free vibration characteristics. It is found that bending deflection reduces with increase in volume fraction of the CNT except for unsymmetrical functional graded beam. The static bending deflection and deformed shape of the beams are significantly influenced by the nature of temperature field. The critical buckling temperature of the beam with symmetric CNT distribution (where CNTs concentration is far from the neutral axis) is greater than other beams under different temperature fields and its value is less when the beams are exposed to uniform temperature rise above ambient temperature compared to other non-uniform temperature variations. However, the critical buckling temperature is not increasing significantly with increase in volume fraction of the CNT. The fundamental buckling mode shape is not sensitive to the nature of temperature variation but bending amplitude of the buckling mode shape is significantly influenced by functional grading of CNT and volume fraction of the CNT. The natural frequency of the beams reduces significantly with increase in temperature and the free vibration mode shapes are not influenced by temperature rise, nature of temperature variation and volume fraction of the CNT.
Multi attribute decision making approaches are used to screen and rank selected materials for piezoelectric applications including ultrasonic transducers and actuators. We have investigated two separate multi attribute decision making techniques namely the technique for order preference by similarity to ideal solution and non-linear simple additive weighting methods to rank and compare selected materials for high and room temperature piezoelectric applications. Subjective weights have been determined using modified digital logic approach. Lead-based piezoceramics acquire all the top ranking positions, indicating their functional superiority among all the selected materials. However, some lead-free materials show comparable performance index with that of the lead-based ceramics. The KNN (K0.5Na0.5NbO3) family in particular shows positive simple additive weighting index, indicating potential lead-free candidates for piezoelectric applications.
The inclusion of particles (micro or nano) is a method to improve the mechanical properties, such as toughness, of structural adhesives. Structural adhesives are known for their high strength and stiffness but also for their low ductility and toughness. There are many processes described in the literature to increase the toughness, the use of rubber particles being one of the most common processes. In the present study, natural micro particles of cork were used with the objective to increase the ductility of a brittle epoxy adhesive. The idea is for the cork particles to act like a crack stopper. The influence of the amount of cork particles was studied. Particles of cork ranging in size from 125 to 250 µm were mixed in the epoxy adhesive Araldite 2020 from Huntsman. The amount of cork in the adhesive was varied between 0.5% and 5% in weight. This evaluation was made using tensile tests and it was evident that the failure strain was related to the amount of cork particles in the resin. The results concerning the single lap joints and the glass transition temperature confirm the increased ductility obtained in the tensile tests.
The purpose of this article is to provide readers with a broad understanding on the deformation mechanics of hole-flanging by incremental sheet forming that will enable them to identify the major operating parameters, to determine the process formability window and to successfully design hole-flanged sheet metal parts. The methodology draws upon the utilization of circle grid analysis, measurement of the gauge length strains at the onset of fracture in a wide range of sheet formability tests, determination of the failure limits by necking and fracture and evaluation of the relative performance of hole-flanging by incremental sheet forming and conventional press-working. The presentation is illustrated with selected test cases obtained from a comprehensive experimental investigation. The overall content of this article widens and enhances previous research work by the authors in the understanding of the deformation mechanics and failure in hole-flanging by incremental sheet forming and includes new experimental data in stainless steel AISI304L.
An original theoretical approach adopted in this article is applied to the structural response of fiber-metal laminate subjected to low-velocity impact of a foreign body. New expressions are derived from the energy balance approach with the inclusion of material plasticity. The important assumption used here is that the fibers in and around the impacted area will fail first, and that the metal layers over this area are in pure membrane state. The nonlinear load versus displacement response of the impactor is thus composed of three parts: indentation, elastic deflection and plastic deflection of the panel. The results of maximum contact force, contact duration and corresponding failure modes are presented, compared and discussed in this technical article.
Investment casting process, also known as lost wax process, is utilized when complex detail, undercuts or non-machinable features and accurate parts are desired. It begins with a wax pattern which is an exact replica of the as cast part. So the properties of the wax patterns are ultimately passed on to the castings. This article highlights the application of utility concept with Taguchi method for the multi-response optimization of wax patterns made by the investment casting process. The wax injection process parameters considered are injection temperature, injection pressure and injection time, whereas the responses are linear shrinkage, surface roughness and penetration, respectively. The experiments are planned as per Taguchi’s L9 orthogonal array. The utility concept converts multi-response optimization problem into single response optimization problem and thereafter Taguchi method is applied. The results indicate that injection pressure is the most significant process parameter influencing the quality characteristic of the wax patterns. The confirmation tests with optimal levels of injection process parameters are carried out to illustrate the efficacy of the proposed method. The results are found to be within the confidence interval. The optimization results revealed that a combination of lower level of injection temperature and injection time along with higher level of injection pressure leads to overall improvement in the quality of the wax patterns. It has also been established that there is some quality loss in terms of surface finish of the wax patterns in multi-response optimization as compared to single response optimization, though an overall improvement in the process is being observed.
The corrosion rate of magnesium alloys is generally too high for biodegradable implant applications. This work explored combinations of anodizing and picosecond laser surface treatments to modify the corrosion response of magnesium alloy AZ31. Anodizing of the AZ31 in NaOH solutions produced porous oxide layer structures. Shallow laser treatment of these anodized surfaces, using low pulse powers, resulted mainly in oxide ablation and impaired corrosion resistance. Higher pulse power, resulting in rapid melting and resolidification into the substrate, provided an improved corrosion response. The refined grain structure produced is approximately only 5 µm deep and therefore has minimal influence on bulk mechanical properties. It is therefore a suitable process for surface modifications on small medical device structures. Controlling the initial point of degradation has been demonstrated by the use of selective laser treatment of the AZ31 surface.
Laser transformation hardening is used to obtain the localized microstructural change, improve wear resistance and hardness to the desired area without affecting the bulk properties. In this study, laser transformation hardening of EN25 steel is performed using a 2 kW continuous wave solid-state neodymium yttrium aluminium garnet laser system. Numerical simulation of laser transformation hardening is carried out by finite element method considering the thermo-physical properties of the material. Based on the numerical simulation the temperature, hardness distribution, hardened depth and width and the phase proportions are determined. The simulation is performed by varying the travel speed of the workpiece. The simulation results are verified with the experimental data and are found to be satisfactory with less than 5% error. It is observed that almost 97% of the phases in the hardened zone is converted into martensite phase with increased hardness about two fold compared to the base material.
An alkali-activated aluminosilicate geopolymer cement was reinforced with polyether ether ketone-wound carbon fibre layers to improve the mechanical properties of the cement in flexion. Such a material, which is heat resistant and has a low coefficient of thermal expansion, will be of use in the development of out-of-autoclave processing routes for large area composite components. The mechanical and physicochemical properties of both the neat and reinforced cement were examined using Charpy impact and three-point bend testing and Fourier transform infrared spectroscopy. A five-fold improvement in flexural strength was observed for the fibre-reinforced geopolymer samples, while a three-fold improvement was observed in the impact strength. The coefficient of thermal expansion of the composite was determined using dilatometry. A number of different curing cycles were also examined using differential scanning calorimetry. The fibre reinforcement led to flexural strength improvement of up to 5 times as well as increasing the strain to failure.
In this study, measurements of nylon 11 pipes subjected to ageing at 40 °C, 70 °C and 100 °C in water, methanol and xylene using both a constant pressure of 200 bar and a cyclic pressure regime are reported. Gravimetric measurements indicate the rate at which the solvent is absorbed by the polymer, and differential scanning calorimetry follows the changes in the crystallinity as the materials are aged. Dramatic changes in the tensile properties are observed when the pipes are subjected to high pressure and reflect a relaxation of the stress in the matrix introduced by the quenching process when the pipes were extruded. The magnitude of the change varies with the fluid and reflects their relative abilities to be absorbed by the polymer. Measurements of the relative viscosity for the polymer indicated that in the case of water and methanol, hydrolytic degradation of the polymer is time-dependent. The impact of the morphological changes in the dynamic mechanical properties revealed the movement of elasticity transition to higher temperatures and reduction in the chain mobility with time. Changes in the mechanical properties are a function of the initial stress relaxation and chain scission as a consequence of degradation and thermodynamically driven morphological changes increasing the crystallinity and embrittling the polymer. As the pipes aged the burst pressures progressively decreased. Examination of the failure surfaces indicated brittle failure and clear evidence of environmental stress cracking. Whilst the data indicate that the pipes might be used effectively for hydrophobic fluids, hydrophilic fluids and in particular methanol can significantly shorten their effective life.
This study of the behaviour of high-density polyethylene umbilical hoses subjected to constant and cyclic variation of pressure and temperatures attempts to simulate the temperatures and stresses experienced in offshore operations. The hoses are used to carry fluids to the top of the wellhead and provide protection for the electrical and optical controls systems. Measurements are reported for exposures at 40°C, 70°C and 100°C in water, methanol and xylene, using an applied pressure of 200 bar. The changes in the physical properties of the hose were monitored by measurement of the tensile properties, dynamic mechanical thermal analysis, differential scanning calorimetry and gravimetric uptake of the fluids. Significant changes occur immediately on application of pressure and reflect changes in crystallinity. The rates and extent of the modifications depend primarily on the ageing temperature but are also influenced by the fluid. Water has little effect on the rate at which ageing occurs, whereas xylene, which is a potential solvent for high-density polyethylene, exhibits characteristics of plasticization. Methanol behaves as a weak solvent and shows characteristics intermediate between xylene and water. Burst tests carried out on the aged material show that significant loss in strength is only observed with the highest temperatures and most aggressive solvent systems. The study indicates that engineers should use pressure-aged rather than initial materials data when designing umbilical hose systems.
A parametric experimental study has been conducted to investigate the combined effect of fly ash, silica fume and polypropylene fiber on freezing–thawing durability of concrete composite. Four fly ash contents, four silica fume contents and five different fiber volume fractions were used. Results reveal that the addition of fly ash has lowered the freezing–thawing durability of concrete composite containing fly ash and that the freezing–thawing durability is decreasing gradually with the increase of fly ash content. It is evident that the addition of silica fume and polypropylene fiber can greatly improve the freezing–thawing durability of the concrete composite containing fly ash and the freezing–thawing durability is enhanced as the silica fume content and the fiber volume fraction increases gradually, with the fiber volume fraction below 0.08%. However, the freezing–thawing durability of concrete composite begins to decline after the fiber volume dosage exceeds 0.08%.
Investment casting is competitive with all other casting processes where the size of the product is within a mutually castable range. Though investment casting is used to produce metal parts of any intricate shapes with excellent surface finish, it suffers from long lead time and high tooling costs, which makes it uneconomical for the production of either single casting, or small and medium production units. These problems could be overcome by the applications of rapid prototyping and rapid tooling technologies for low-volume investment casting production runs. The present article analyzes different classifications of rapid prototyping techniques and it reviews various investigations made on the usability of rapid prototyping- and rapid tooling-integrated investment casting process, with their advantages and limitations. The emerging areas of applications of rapid prototyping like dentistry, jewelry, surgical implants, turbine blades, etc., are accordingly discussed. Further, an elaborate discussion is made on the application of newer technologies for directly developing ceramic shells. This article also emphasizes on various future scopes possible in rapid prototyping-integrated investment casting process.
Average plastic properties of friction stir-welded AA2024-T3 are obtained by coupling novel small punch beam testing with a neural network algorithm. The small punch beam test utilizes a cylindrical punch head and miniature rectangular beam specimens. The specimens may be manufactured by material removed from in-service components with minimal effect on mechanical performances. Specimen preparation, material model, and identifying procedure are systematically presented. Predicted load–displacement results agree well with the experimental results and the identified strain–stress relationship demonstrates useful agreement with tensile test. Since the load–displacement curve is insensitive to base material properties, knowledge of these properties is not required in the proposed method.
Two commercial Zn–Al alloys, constituting a natural composite consisting of ductile fibres of face-centred cubic aluminium in the less ductile close-packed hexagonal Zn-rich matrix, variously subjected to warm rolling and warm equal channel angular processing, were investigated to examine the factors governing strength and ductility. Comparison with the published behaviour of an aluminium–copper alloy subjected to similar treatment suggested that the observed behaviour and the interpretation offered were general. When strong crystallographic orientation occurred — as in rolling — strength, and to a less extent ductility, largely depended on crystallographic orientation; ductility strongly depended on the processing route (rolling or equal channel angular processing), but the diffuse orientation characteristic of equal channel angular extrusion allowed the inverse Hall–Petch parameter (as a measure of filament thickness) to display a role in that case. High ductility of the rolled material correlated with orientation of a large number of grains of the close-packed hexagonal matrix phase for easy slip. Strengthening by reduction in size of the units of structure is likely to be available in metallic composites only when dislocation hardening substantially outweighs orientation softening.
Assessment of different higher order shell theories for low-velocity impact response analysis of simply-supported fibre-metal laminate circular cylindrical shells is achieved. A new two-degree-of-freedom spring-mass model is adapted and used for contact force history estimation. The Fourier series method is used to solve the governing equations of fibre-metal laminate shell. The mechanical behaviour of fibre-metal laminate is assumed to be elastic. The impact behaviour is assumed to be quasi-static. In order to investigate the effect of the thickness flexibility on the impact response analysis of fibre-metal laminate cylindrical shells, different 2D and 3D higher order shell theories are evaluated. Also, effects of some parameters including metal volume fraction and fibre-metal laminate layup on the impact response are investigated. The results indicate that regardless of the fibre-metal laminate layup, as the value of metal volume fraction increases, the influence of the thickness flexibility on the impact response of fibre-metal laminate cylindrical shells is more significant. Also, as the metal volume fraction increases, the impulse (area under contact force–time) remains almost unchanged. In fact, the fundamental frequency of the shell governs both the peak value of the contact force as well as the contact duration. It is shown that Al/G 2/1 is the best layup to minimise the shell deflections due to impact load and to maximise the fundamental frequency.
In this research, the effect of heating on the mechanical alloying process for synthesizing of titanium carbide was investigated. Raw materials containing pure titanium and graphite powders were milled in different times and temperature. In order to detect phases and properties of synthesized materials X-ray diffraction was applied. Physical properties including density and specific surface area along with microstructure were studied. Results showed that heating can accelerate the mechanical alloying process. By increasing the temperature during milling, production mechanism of titanium carbide changed from self-propagating high-temperature synthesis to gradual model. Changes of density confirmed this phenomenon too. Increasing the milling time leads to particle size and crystal of synthesized titanium carbides became finer down to nanometer scale. Because of higher effective time span of produced titanium carbide, increasing the temperature produces finer particle sizes of powders in similar milling time.
In this article numerical model for prediction of phase evolution of Ti-6Al-4V titanium alloy was presented. In particular, attention was focused on alpha to beta and beta to alpha+beta phase transformations. The analysis was conducted using a commercial implicit finite element method code, considering the data and the parameters of a real case study to check the quality of the numerical model. The alpha to beta transformation was developed using the simplified form of the Avrami model and the beta to alpha+beta transformation was controlled through the generalized Avrami model. The model so-thought has been used to conduct a 2D simulation of a forging process. A comparison between the numerical and experimental data indicates that the model can be utilized as base for a design tool in complex hot-forging processes of titanium alloys.
Residual stresses, local mechanical properties, and microstructural evolution in terms of grain structures and precipitation distribution have been studied in friction stir welding of AA2017 in T4 and T6 conditions. Microstructural studies including optical and electron microscopy were made to characterize the developed microstructures in different zones of the weldment. Furthermore, X-ray diffraction technique and digital image correlation technique were also utilized to assess residual stress and mechanical properties of the welded alloy. The results show that coarsening of semi-coherent plate-shaped precipitates and formation of incoherent spherical-shaped particles occur in heat affected and thermo-mechanical affected zones while a non-uniform grain size distribution is formed in the stir zone because of asymmetric distribution of temperature. Moreover, the developed residual stresses in the welded samples significantly enhance the effect of subsequent natural aging.
This article presents an extensive experimental investigation of singly curved fibre-reinforced composite structures subjected to low energy heavy mass impact. The objective of the study is to understand the contribution the surface ply orientation makes to the resistance of the impact strike and the impact behaviour of composite cylinders of different stacking configuration. Tests were conducted on laminate configurations suitable for various structural applications, using an instrumented drop-weight (30 kg) device. Impact studies conducted were on half single curved symmetrical composite panels of (β2/452/-452/02/902)s stacking configuration, where β = 0, 30, 45, 60, 90 and also on fully single curve composite cylinders of stacking sequence (02/452/902/-452)s, (452/02/902/-452)s and (902/452/02/-452)s. The test samples were manufactured by the hand lay-up technique using unidirectional carbon fibre–epoxy matrix prepregs. The impact properties such as the absorbed energy, bending stiffness, saturation energy, damage degree and the contact period were obtained from the response data and interpreted to establish the impact effect on the composite structure. From this unique study, it was realised that surface ply orientation of half single curved composites significantly contributes to the energy absorption characteristics and that the damage effect was most severe for the (902/452/02/-452)s configuration of the composite cylinder.
The exact three-dimensional piezo-thermo-mechanical solution for a finite cylindrical composite panel composed of cross-ply and piezoelectric laminate is presented in this article. The panel is simply supported at four end edges and is subjected to thermo-mechanical loadings on its top and bottom surfaces, respectively. The piezoelectric layers are polarized along radial direction as a sensor. The variables are expanded layerwise in Fourier series to satisfy the boundary conditions at the simply supported ends. As an example, a cross-ply laminated cylindrical panel made of alumina fiber reinforced aluminum composite, associated with a piezoelectric material of crystal class mm2 is calculated. Furthermore, some numerical results for the temperature change, the displacement, stresses, electric potential, and electric displacement distributions are shown in figures and briefly discussed.
This study describes the influence of Fe (wt%) on the microstructure, hardness, and wear behavior of Al–18Si–4Cu–0.5Mg–XFe (X = Fe, at 0.4, 2.0, and 5.0 wt%) hypereutectic Al–Si alloy. The range of alloys was selected on the basis of literature study. The literature revealed that most of the studies on the effect of iron have been focused on either hypo-eutectic Al–Si alloys or lower levels of iron in the alloy. As Fe-rich intermetallic compounds are high melting point compounds, it is expected that they should improve the high temperature strength of the Al–Si alloys. The higher iron contents were specifically selected to obtain the advantage of high temperature stability leading to high wear resistance. Microstructure has been characterized using optical microscopy, scanning electron micrography, and image analysis studies. Maximum hardness of the alloy was obtained when solutionized (at 500 °C) for 4 h followed by artificial aging (at 190 °C) for 6 h. Heat-treated samples with only maximum hardness were further tested for wear behavior. The wear behavior of alloy in the as-cast and heat-treated conditions has been analyzed using Taguchi approach and analysis of variance analysis to find out the factors that affect wear significantly.
A parametric experimental study has been conducted to investigate the effect of silica fume on the durability of the concrete composites. Four different silica fume contents (3%, 6%, 9% and 12%) were used. The durability of concrete composites includes water impermeability, dry shrinkage property, the carbonation resistance and the freeze–thaw resistance. The results indicate that the addition of silica fume has a little adverse effect on the dry shrinkage property of concrete composites. With the increase of silica fume content, the dry shrinkage strain is increasing gradually. However, the addition of silica fume has greatly improved the water impermeability, the carbonation resistance and the freeze–thaw resistance of concrete composites. With the increase of silica fume content, the length of water permeability and the carbonation depth of the specimens are decreasing gradually, and the relative dynamic elastic modulus of the specimens has a tendency of increase with the increase of silica fume content.
Experimental investigation and finite element analysis model has been developed to study the physical, mechanical, thermal and thermo-mechanical behavior of titania (TiO2) (0, 4, 8 and 12 wt%) filled zinc–aluminium (ZA-27) alloy composite materials fabricated by stir casting techniques. The experimental thermal conductivity are measured and compared with both theoretical and finite element analysis model results. The error between experimental-Hasselman & Johnson model and experimental-finite element simulation for 4 wt% of TiO2-filled composite is 2.43% and 0.81% while for 8 wt% of TiO2-filled composite is 2.60% and 1.73% and for 12 wt% of TiO2-filled composite is 11% and 1.9% respectively in longitudinal direction. Similarly, in transverse direction the error lies between experimental-Hamilton & Crosser model and experimental-finite elemet simulation for 4 wt% of TiO2-filled composite is 2.62%, 3.19%, while for 8 wt% of TiO2-filled composite is 1.42%, 1.45% and for 12 wt% of TiO2-filled composite is 5.76% and 3.64%, respectively. The thermo-mechanical characteristics of the particulate-filled alloy composites are investigated in the temperature range of 80–400 °C with the single cantilever technique using dynamic mechanical analyzer. The composites with 12 wt% of TiO2 filled has been observed to exhibit superior thermo-mechanical response with highest energy dissipation/damping ability accompanied with a constant storage modulus without any substantial decay till 125 °C. Finally, the stress intensity factor for all the particulate-filled composites is studied experimentally and compared with finite element method results. The results obtained from this analysis facilitate to understand the fracture propagation in the composites.
In the present study, the corrosion behavior of Nickel-base coatings on carbon steel as a substrate was analyzed. The samples were coated using a high velocity oxy-fuel thermal spray technique. In order to investigate the effects of spray variables on coating quality as compared with corrosion behavior of NiCr alloy in NaCl 3.5% solution, six design experiments were considered. The NiCr powder alloy contained 20% Cr. The sprays variables were fuel: oxygen, 1.07 and 1.25 both in reduction condition and also the powder feed rate 18, 27 and 36 g/min were selected. The high velocity oxy-fuel coated samples were corrosion tested using the potentiostatic polarization tester. Analyzing the polarization graph allowed the selection of the optimum operating conditions to achieve the desired specifications of the high velocity oxy-fuel coatings for their best corrosion resistance in the chosen environment. The samples structures were characterized by a scanning electron microscopy, energy-dispersive X-ray spectroscopy analysis and X-ray diffraction. The analysis of the results indicated that the fuel/oxygen and the powder feed rate have a significant effect on the porosity and corrosion resistance of these coatings. Corrosion behavior of the sample coated by fuel: oxygen 1.25 and powder feed rate 18 g/min was the best.
A study on the flexural properties of hybrid glass and carbon fiber reinforced epoxy composites is presented in this article. Three combinations of the carbon and glass fibers, i.e. S-2&T700S, S-2&TR30S and E&TR30S, were chosen to make hybrid composite specimens. Specimens were made by the hand lay-up process in an intra-ply configuration with varying degrees of glass fibers added to the surface of a carbon laminate. These specimens were then tested in the three-point bend configuration in accordance with ASTM D790-07 at a span to depth ratio of 32. The failure modes were examined under an optical microscope, and it was found that the dominant failure mode was compressive failure. The flexural behavior was also simulated using finite element analysis, and the flexural modulus, flexural strength and strain to failure were calculated. Both the experiments and finite element analysis suggest flexural modulus decreases with increasing percentage of glass fibers. Positive hybrid effects exist by substituting carbon fibers with glass fibers on the compressive surface.
The goal of this research was improving elastomeric seal performance based on seal material design. The specific seal failure mode considered was permanent deformation or compression set of O-rings, and sealing performance degradation due to this process is common to all types of elastomeric seals. The basis for seal design was identified as reducing the elastic strain energy in the seal since it drives the growth of permanent material deformation. The design concept developed was using variation of material behavior over the seal section to manipulate the level and distribution of elastic strain energy. Design studies used finite element analyses with experimentally measured material behavior to quantify effects of varying seal material characteristic on seal performance. Sealing performance was described in terms of compression set and seal-counterface contact pressure. Experimental O-rings were produced based on designs that included regions of less stiff material in the larger surrounding seal section. Performance of new design seals was compared to conventional one-material seals and improved sealing performance was demonstrated. With the modified design seals, both compression set and the rate of sealing contact pressure loss over time were decreased. There was a loss of initial maximum contact pressure with the inclusion of less stiff material regions, but it was shown that this effect can be mitigated by properly locating the softer material in the overall seal section. In summary, properly implemented material variations over the seal will result in lower strain energy content, lower rate of permanent deformation development and decreasing rate of loss of seal-counterface contact pressure.
A parametric experimental study has been conducted to investigate the effect of silica fume on the fracture properties of high-performance concrete containing fly ash, with four silica fume contents (3%, 6%, 9% and 12%) used. By means of three-point bending method, the fracture toughness, fracture energy, effective crack length, critical crack opening displacement and maximum crack opening displacement of the specimen were measured, respectively. The results indicate that silica fume has great adverse effect on the fracture toughness, fracture energy, effective crack length, critical crack opening displacement and maximum crack opening displacement, and these fracture parameters decrease gradually when the content of silica fume increases from 3% to 12%. Besides, as the silica fume content increases from 3% to 12%, the relational curves between the vertical load and the mid-span deflection (PV–), crack mouth opening displacement (PV–CMOD) and crack tip opening displacement (PV–CTOD) are becoming thinner and thinner, which indicates that the capability of high-performance concrete containing fly ash to resist crack propagation is becoming weaker and weaker. It seems that the content of silica fume of high-performance concrete containing fly ash should be controlled strictly, and the silica fume content should be as low as possible on condition that the other properties of high-performance concrete can meet practical requirements.