Materials and Design

Published by Elsevier
Online ISSN: 0264-1275
Publications
Article
One major obstacle to human space exploration is the possible limitations imposed by the adverse effects of long-term exposure to the space environment. Even before human spaceflight began, the potentially brief exposure of astronauts to the very intense random solar energetic particle (SEP) events was of great concern. A new challenge appears in deep space exploration from exposure to the low-intensity heavy-ion flux of the galactic cosmic rays (GCR) since the missions are of long duration and the accumulated exposures can be high. Since aluminum (traditionally used in spacecraft to avoid potential radiation risks) leads to prohibitively expensive mission launch costs, alternative materials need to be explored. An overview of the materials related issues and their impact on human space exploration will be given.
 
Compositions of materials.
Article
The age hardening behavior of Al–4.5%Cu alloy composite reinforced with zircon sand particulates and produced by stir casting route has been investigated in different quenching media viz, water, oil, and salt brine solution (7 wt%). Optical microscopy of the as cast alloy composite indicates that the matrix of the composite has the cellular structure. Copper rich CuAl2 precipitates have been found near particle matrix interface. The results of ageing demonstrate that the microhardness of age hardenable Al–Cu based alloy composites depend on the quenching medium in which they are heat treated. Salt brine quenching is faster as compared to water and oil, even if higher strength is obtained but cannot be used for complex shapes and thin sections where oil quenching is the alternative due to minimum distortion and cracking problems. Thermal cycling studies of the composite at 25–540 °C have been also carried out to determine the extent of quenching of the matrix after each solution heat treatment cycle while varying the quenching media.
 
Article
We focus on a successive response surface method for the optimization problems. The response surfaces are built using Moving Least Squares approximations constructed within a moving region of interest. Our first approach is an extension of pattern search algorithms with a fixed pattern panned and zoomed in a continuous manner across the design space. In the second one, the region of interest moves across a predefined discrete grid of authorized experimental designs. Two applications of the sheet metal forming process are used to demonstrate the robustness of the method. We use the one-step Inverse Approach as a surrogate model during the optimization. The final design is validated with Stampack®, Ls-Dyna® and Abaqus® commercial codes based respectively on explicit dynamic and implicit static approaches.
 
Article
As alternatives to the classical finite element model (FEM), a meshless smooth particle hydrodynamics (SPH) method, in which the discrete particles represent a solid domain, and a coupled FEM/SPH modeling technique were investigated for the numerical simulation of the quasi-static axial crushing of polystyrene foam-filled aluminum thin-walled aluminum tubes. The results of numerical simulations, load-deformation histories, fold lengths and specific absorbed energies, were found to show satisfactory correlations with those of experiments and FEM. The results further proved the capabilities of the SPH Method and coupled FEM/SPH modeling technique in predicting the crushing behavior of foam-filled thin-walled tubes.
 
Article
In this paper the blast resistance of cracked steel structures repaired with fibre-reinforced polymer (FRP) composite patch are investigated. The switch box which has been subjected to blast loading is chosen to study. The steel material is modelled using isotropic hardening model, pertaining to Von Mises yield condition with isotropic strain hardening, and strain rate-dependent dynamic yield stress based on Cowper and Symonds model. Three different cracked structures are chosen to investigate their capability in dissipating the blast loading. To improve the blast resistance, the cracked steel structures are stiffened using carbon fibre-reinforced polymer (CFRP) composite patches. The repaired patches reduce the stress field around the crack as the stress is transferred from the cracked zone to them. This situation prevents the crack from growing and extends the service life of the steel structure. It will be shown that CFRP repairing can significantly increase the blast resistance of cracked steel structures.Research highlights► To simulate the blast response of steel box structures using LSDYNA. ► To predict the blast resistance of cracked box structure subjected to blast loading. ► To improve the blast resistance of cracked box structures by CFRP composite materials. ► To investigate the effect of laminate design, thickness and crack orientation on blast resistance of cracked box structures.
 
Trend of research in material screening and choosing methods. 
Classification of screening methods in material selection.  
Classification of material choosing methods.  
Article
The selection of a material for a specific engineering purpose is a lengthy and expensive process. Approximately always more than one material is suitable for an engineering application, and the final selection is a compromise that brings some advantages as well as disadvantages. One of the issues that emerges from this review is that regardless of the relation of design stages and process selection with material selection, screening and ranking are two vital steps in the material selection. A variety of quantitative selection procedures have been developed to solve this issue, so that a systematic evaluation can be made. This paper seeks to address the following questions: (1) what is the contribution of the literature in the field of screening and choosing the materials? (2) What are the methodologies/systems/tools for material selection of engineering components? (3) Which approaches were prevalently applied? (4) Is there any inadequacy of the approaches? This research not only provides evidence that the multi-criteria decision making approaches has the potential to greatly improve the material selection methodology, but also aids the researchers and decision makers in applying the approaches effectively.
 
Article
The objective of this study was to investigate the effects of material compositions on the mechanical properties of wood–plastic composites (WPCs) manufactured by injection molding. Using a ratio of wood flour/plastic matrix/MAPP (maleic anhydride polypropylene)/zinc stearate of 47:47:3:3, the tensile strength and modulus of rupture (MOR) of WPCs manufactured with LDPE (low-density polyethylene) and PP (polypropylene) were found to be larger than those of LDPE and PP themselves. However, contrasting findings were obtained when the polymer matrix was ABS (acrylonitrile-butadiene-styrene). In comparison to the mechanical properties of RPP (recycled polypropylene) itself, the MOR increased and the tensile strength decreased for WPCs manufactured with RPP.The tensile strength, MOR, and storage modulus of WPCs made from PP mixed with 47% wood flours (<180 μm) and 3–4.5% MAPP were larger than those of the other WPCs manufactured in this study. However, the polymer damping peaks showed a contrary result.
 
Article
The performance of a combustion engine is closely related to the friction force and wear between cylinder liner and piston rings. It is believed that this friction force can be significantly reduced by optimizing the surface topography of cylinder liners. Therefore, it is necessary to understand how liner surface topography affects wear, friction and lubricating oil consumption. Several experimental studies have been carried out for evaluating wear and friction in simulated engine conditions using Cameron–Plint wear testers, Pin-on-disk testers, SRV testers, etc. However, these studies do not reflect the true behaviour of inside the engine because of stroke length limitations. In this paper, a non-firing engine simulator has been developed in order to simulate engine conditions to a closer extent compared to these machines. This simulator can operate at similar linear speed, stroke, and load as real engine and can simulate almost all engine operating conditions, except firing pressures. In the present study, a production grade cylinder liner has been used for the experiments conducted using a custom-made non-firing engine simulator. The wear and surface property behaviour were evaluated at several locations in the liner and found that after running-in an engine, surface of cylinder liner exhibits plateau-honed-like characteristic. Energy dispersive analysis (EDS) has been carried out of liner and top ring for evaluating materials transfer. Coefficient of friction between three different liner segments and ring was evaluated using an SRV wear tester. Coefficient of friction in the piston ring–liner interface increases with increasing average surface roughness for liner.
 
Article
This paper presents a methodology for the selection of joining process in design, implemented in software. The method captures important coupling between the process options, material and design detail, using databases assembled by discussion with experts on mechanical fastening, welding and adhesives. The approach first eliminates solutions that are not technically feasible, with reasons, and then ranks the remaining solutions on the basis of the degree of agreement with the set of design requirements (using a fuzzy logic algorithm). The software implementation presents the designer with a questionnaire, to assemble the set of requirements in terms of the joint geometry, the materials to be joined, the functions required from the joint, and production conditions. Consideration is also given to other ‘local’ factors that may influence the selection, such as the availability of equipment and necessary skills, or current practice. The application of the methods using the software is illustrated by a case study. The selection tool successfully restricts the number of processes to be evaluated further in a given design, for example, before undertaking the more difficult task of detailed cost evaluation. The method is also successful in suggesting modifications to the design to facilitate joining, or indicating possible innovative use of unfamiliar processes.
 
Article
Ranking and choosing the best material is one of most important stages in material selection process. Using linear assignment method, the multi-criteria decision making (MCDM) approach is proposed in decision-making process to rank the materials for a given engineering component with respect to several criteria. The proposed material selection procedure is relatively simple, and can be a useful approach when material selection problem includes qualitative properties or user-interaction aspects. The suggested approach also can be use for quantitative properties. Three examples are included to demonstrate the suggested method. Result of proposed approach showed good agreement with other methods.
 
Article
Engineering design draws on tens of thousands of materials and on many hundreds of processes to shape, join and finish them. One aspect of optimized design of a product or system is that of selecting, from this vast menu, the materials and processes that best meet the needs of the design, maximizing its performance and minimizing its cost. The problem, still incompletely solved, is that of matching material and process attributes to design requirements. Some of these attributes can be expressed as numbers, like density or thermal conductivity; some are Boolean, such as the ability to be recycled; some, like resistance to corrosion, can be expressed only as a ranking (poor, adequate, good, for instance); and some can only be captured in text and images. Achieving the match with design requirements involves four basic steps. (1) A method for translating design requirements into a specification for material and process. (2) A procedure for screening out those that cannot meet the specification, leaving a subset of the original menu. (3) A scheme for ranking the surviving materials and process, identifying those that have the greatest potential. (4) A way of searching for supporting information about the top-ranked candidates, giving as much background information about their strengths, weaknesses, history of use and future potential as possible. In this paper we review the strategies that have evolved to deal with this problem, the progress that has been made and the challenges that remain.
 
Article
In industrial forming processes, the metals and alloys are subject to complex strain, strain-rate, and temperature histories. Understanding the flow behaviors of metals and alloys in hot working has a great importance for designers of metal forming processes. In order to study the workability and establish the optimum hot formation processing parameters for some metals and alloys, a number of research groups have made efforts to carry out the thermo-mechanical experiments (compressive, tensile and torsion tests) over wide forming temperatures and strain-rates, and some constitutive equations were developed to describe the hot deformation behaviors. This paper presents a critical review on some experimental results and constitutive descriptions for metals and alloys in hot working, which were reported in international publications in recent years. In this review paper, the constitutive models are divided into three categories, including the phenomenological, physical-based and artificial neural network models, to introduce their developments, prediction capabilities, and application scopes, respectively. Additionally, some limitations and objective suggestions for the further development of constitutive descriptions for metals and alloys in hot working are proposed.
 
Flexural behaviour of areca fibers reinforced urea formaldehyde composites.  
Chemical composition of natural fibers.
Flexural behaviour of areca fibers reinforced melamine urea formaldehyde composites.  
Flexural behaviour of areca fibers reinforced epoxy composites.  
Flexural strength of areca composites.  
Article
Natural fibers are considered to have potential use as reinforcing agents in polymer composite materials because of their principle benefits: good strength and stiffness, low cost, and be an environmental friendly, degradable, and renewable material. A study has been carried out to evaluate physical, flexural and impact properties of composite made by areca fibers with randomly distributed fibers. The extracted areca fibers from the areca husk were alkali treated with potassium hydroxide to get better interfacial bonding between fiber and matrix. Then composite laminates were fabricated by using urea formaldehyde, melamine urea formaldehyde and epoxy resins by means of compression molding technique with varying process parameters, such as fiber condition (untreated and alkali treated), and fiber loading percentages (50% and 60% by weight). The developed areca fiber-reinforced composites were then characterized by physical, bending and impact test. The results show that flexural and impact strength increases with increase in the fiber loading percentage. Compared to untreated fiber, significant change in flexural and impact strength has been observed for treated areca fiber reinforcement.Research highlights► Alkali treated fibers have higher intrinsic fiber strength than untreated fibers. ► Areca-epoxy has moderately higher flexural and impact strength compared to others. ► Areca fibers have a promising future in the natural fibers composite industry.
 
Different SEM images for the FEA analysis: (a) SEM1, (b) SEM2, (c) SEM3, (d) SEM4, and (e) SEM5.
Stress-strain behavior of different SEM image based FEA models. 
Stress distribution of SEM image based FEA models. 
Maximum stress induced in the particle for different SEM based FEA models. 
Micrograph showing the particle fracture near the fracture surface. 
Article
This paper discusses the methodology of microstructure based elastic–plastic finite element analysis of particle reinforced metal matrix composites. This model is used to predict the failure of two dimensional microstructure models under tensile loading conditions. A literature survey indicates that the major failure mechanism of particle reinforced metal matrix composites such as particle fracture, interfaces decohesion and matrix yielding is mainly dominated by the distribution of particles in the matrix. Hence, analyses were carried out on the microstructure of random and clustered particles to determine its effect on strength and failure mechanisms. The finite element analysis models were generated in ANSYS, using scanning electron microscope images. The percentage of major failures and stress–strain responses were predicted numerically for each microstructure. It is evident from the analysis that the clustering nature of particles in the matrix dominates the failure modes of particle reinforced metal matrix composites.
 
Article
In this study, corrosion behaviour of ultrafine-grained (UFG) commercial pure aluminium Al 1050 processed by rotary swaging (RS) was examined using potentiodynamic polarization and weight loss immersion test in 3.5% NaCl solution. Corrosion behaviour of UFG Al 1050 was compared with that of coarse grained (CG) as-received material. The results showed that ultrafine grain refinement by RS led to marked improvement of the corrosion resistance. The improvement in corrosion resistance is profited from the denser and stable passive film due to more grain boundaries, larger fraction of non-equilibrium grain boundaries and residual stress of the UFG pure aluminium. The weight loss tests revealed low corrosion rate values of RS material compared to CG as-received material. Scanning electron microscopy (SEM) analysis revealed a higher number of rectangular shallow pits (more close to patches of general dissolution); larger pits size was observed in the as-received compared to RS materials.
 
Article
One of the main concerns in cladding Inconel 625 superalloy on desired substrates is deterioration of corrosion resistance due to cladding process. The present study aims to compare the effect of fusion cladding and explosive cladding procedures on corrosion behavior of Inconel 625 cladding on plain carbon steel as substrate. Also, an attempt has been made to investigate the role of load ratio and numbers of fusion layers in corrosion behavior of explosive and fusion cladding Inconel 625 respectively. In all cases, the cyclic polarization as an electrochemical method has been applied to assess the corrosion behavior. According to the obtained results, both cladding methods aggravate the corrosion resistance of Inconel 625. However, the fusion cladding process is more detrimental to nonuniform corrosion resistance, where the chemical nonuniformity of fusion cladding superalloy issuing from microsegregation, development of secondary phases and contamination of clad through dilution hinders formation of a stable passive layer. Moreover, it is observed that adding more fusion layers can enhance the nonuniform corrosion resistance of fusion cladding Inconel 625, though this resistance still remains weaker than explosive cladding superalloy. Also, the results indicate that raising the impact energy in explosive cladding procedure drops the corrosion resistance of Inconel 625.
 
Article
The relatively new welding process friction stir welding (FSW) was applied in this research work to join 6 mm thick dissimilar aluminum alloys AA5083-H111 and AA6351-T6. The effect of tool rotational speed and pin profile on the microstructure and tensile strength of the joints were studied. Dissimilar joints were made using three different tool rotational speeds of 600 rpm, 950 rpm and 1300 rpm and five different tool pin profiles of straight square (SS), straight hexagon (SH), straight octagon (SO), tapered square (TS), and tapered octagon (TO). Three different regions namely unmixed region, mechanically mixed region and mixed flow region were observed in the weld zone. The tool rotational speed and pin profile considerably influenced the microstructure and tensile strength of the joints. The joint which was fabricated using tool rotational speed of 950 rpm and straight square pin profile yielded highest tensile strength of 273 MPa. The two process parameters affected the joint strength due to variations in material flow behavior, loss of cold work in the HAZ of AA5083 side, dissolution and over aging of precipitates of AA6351 side and formation of macroscopic defects in the weld zone.
 
Article
Development of welding procedures to join aluminum matrix composite (AMCs) holds the key to replace conventional aluminum alloys in many applications. In this research work, AA6061/B4C AMC was produced using stir casting route with the aid of K2TiF6 flux. Plates of 6 mm thickness were prepared from the castings and successfully butt joined using friction stir welding (FSW). The FSW was carried out using a tool rotational speed of 1000 rpm, welding speed of 80 mm/min and axial force of 10 kN. A tool made of high carbon high chromium steel with square pin profile was used. The microstructure of the welded joint was characterized using optical and scanning electron microscopy. The welded joint showed the presence of four zones typically observed in FSW of aluminum alloys. The weld zone showed fine grains and homogeneous distribution of B4C particles. A joint efficiency of 93.4% was realized under the experimental conditions. But, FSW reduced the ductility of the composite.
 
Article
Fly ash has gathered widespread attention as a potential reinforcement for aluminum matrix composites (AMCs) to enhance the properties and reduce the cost of production. Aluminum alloy AA6061 reinforced with various amounts (0, 4, 8 and 12 wt.%) of fly ash particles were prepared by compocasting method. Fly ash particles were incorporated into the semi solid aluminum melt. X-ray diffraction patterns of the prepared AMCs revealed the presence of fly ash particles without the formation of any other intermetallic compounds. The microstructures of the AMCs were analyzed using scanning electron microscopy. The AMCs were characterized with the homogeneous dispersion of fly ash particles having clear interface and good bonding to the aluminum matrix. The incorporation of fly ash particles improved the microhardness and ultimate tensile strength (UTS) of the AMCs.
 
Article
Aluminum rich intermetallic particles are potential reinforcements for discontinuously reinforced aluminum matrix composites (DRAMCs). The objective of the present work is to produce AA6061/Al3Ti and AA6061/Al3Zr composites using in situ casting technique and applying friction stir processing (FSP) to enhance the distribution and morphology of Al3Ti and Al3Zr particles. AA6061/Al3Ti and AA6061/Al3Zr DRAMCs were produced by the in situ reaction of inorganic salts K2TiF6 and K2ZrF6 with molten aluminum. The microstructure was observed using optical and scanning electron microscopy. AA6061/Al3Ti DRAMC exhibited clusters of Al3Ti particles while the segregation of needle shape Al3Zr particles was observed in AA6061/Al3Zr DRAMC. The prepared composites were subjected to FSP. Significant changes in the distribution and morphology of Al3Ti and Al3Zr particles were observed after FSP. The changes in microhardness and sliding wear behavior of AA6061/Al3Ti and AA6061/Al3Zr DRAMCs before and after FSP is detailed in this paper.
 
Article
Creep-aging forming, combining both the aging treatment and forming process, has recently drawn much attention of researchers. In this study, the effects of creep-aging processing on the corrosion resistance of an Al–Zn–Mg–Cu alloy are studied. Results show that the corrosion resistance of the studied Al–Zn–Mg–Cu alloy is sensitive to creep-aging processing parameters (creep-aging temperature and applied stress). With the increase of creep-aging temperature, the corrosion resistance first increases and then decreases. Increasing the applied stress can deteriorate the electrochemical corrosion resistance and improve the exfoliation corrosion resistance. The creep-aging processing can change the size and distribution of precipitates in the aluminum matrix, which significantly affects the corrosion resistance. The discontinuous grain boundary precipitates and narrow precipitate-free zones can enhance the corrosion resistance.
 
Article
In this paper, we have investigated the use of a re-scanning strategy to prevent propagation of macro-cracks during the selective laser melting of an Al85Ni5Y6Co2Fe2 bulk metallic glass composites (BMGCs). These cracks form as a result of the high residual stress caused by the rapid heating and cooling of the material by the laser beam. Unlike crystalline materials, the BMGCs possess a supercooled liquid region in which the residual stress can be relieved by plastic flow. We show that by using a high power initial scan (designed to melt the material) followed by a lower power re-scan (for stress relief) cracking can be prevented. Using this approach, crack-free Al85Ni5Y6Co2Fe2 BMGCs components have been fabricated, including a gear with a diameter ∼25 mm and height ∼10 mm.
 
Article
The purpose of this study is to investigate the effects of vanadium addition on the microstructure and mechanical properties of AlCoCrFeNiVx (x values in molar ratio, x = 0, 0.2, 0.5, 0.8, 1.0) alloys. All the alloys were found to display a crystalline structure of simple body centered cubic (BCC). For AlCoCrFeNi and AlCoCrFeNiV0.2 alloys, Cr and Fe elements segregated to the center of grain while Al and Ni elements segregated to the rest areas. With the increase of V content exceeding to x = 0.5, the homogenized polycrystalline grain can be obtained. For AlCoCrFeNiV0.2 alloy, the compressive strength and plastic strain were as high as 3297.8 MPa and 26.8%, respectively, which were rare in high entropy alloys to date. The fine nanoscale spinodal decomposition microstructure was a key factor for the high fracture strength of AlCoCrFeNiV0.2 alloy. The values of Vickers hardness increased from HV534 to HV648.8 with the increase of V content. The solid-solution strengthening of the body centered cubic matrix was found as the main factor that strengthened the alloys. With the increase of V contents from x = 0 to x = 1.0, the transformation of ferromagnetic behavior to paramagnetic behavior takes place.
 
Microstructural characteristics of samples: inverse pole figure map (a), frequency vs. misorientation map (b) and grain size distribution (c) of as-received sheets, respectively; (d), (e) and (f) are those of as-processed sheets, respectively.
Variation of elongations of ZK60 Mg alloy sheets as a function of the correlated yield strengths.
Article
Thin ZK60 magnesium alloy sheets with ultrafine-grain structure were successfully fabricated by continuous cold rolling with proper intermediate annealing treatments at 503–523 K for 30 min. Meanwhile, microstructure uniformity and planar texture anisotropy were strikingly improved by rolling deformation and static recrystallization, resulting in continuous improvement in the strength anisotropy. Excellent ductility more than 30% in fracture elongation was achieved after further annealing treatment at a lower temperature of 473 K. This was primarily attributed to the significant weakening of the {0 0 0 2} pole intensity and grain refinement during the process. It is shown that mechanical properties of the final sheets could be closely controlled by the present process.
 
Article
The hot tensile deformation behaviors of an Al–Zn–Mg–Cu alloy are studied by uniaxial tensile tests under the deformation temperature of 340–460 °C and strain rate of 0.01–0.001 s−1. The effects of deformation temperature and strain rate on the hot tensile deformation behaviors and fracture characteristics are discussed in detail. The Arrhenius-type constitutive model is developed to predict the peak stress under the tested deformation condition. The results show that: (1) The true stress–true strain curves under all the tested deformation conditions are composed of four distinct stages, i.e., elastic stage, uniform deformation stage, diffusion necking stage and localized necking stage. The flow stress decreases with the increase of deformation temperature or the decrease of strain rate. (2) The elongation to fracture increases with the increase of deformation temperature. Under the tested conditions, the strain rate sensitivity coefficient varies between 0.1248 and 0.2059, which indicates that the main deformation mechanism is the lattice diffusion-controlled dislocation climb. (3) The localized necking causes the final fracture of specimens under all the deformation conditions. Microvoids coalescence is the main fracture mechanism under relatively low deformation temperatures. With the increase of deformation temperature, the intergranular fracture occurs. (4) The peak stresses predicted by the developed model well agree with the experimental results, which indicate the validity of the developed model.
 
Article
In order to investigate the effect of twinning–detwinning on the mechanical properties of AZ31 extruded magnesium alloy pre-compression and pre-stretch deformation were conducted along extrusion direction (ED) at 1%, 3%, 5% strain levels. After pre-strain, the strain-path was inverted by performing tensile or compressive tests at room temperature. Results showed that the detwinning behavior occurred during the inverse tension after the pre-compression. Although due to the aforementioned effect the tensile yield strength decreased, by increasing the pre-compressive levels both fracture elongation and peak strength improved. In the inverse compressive tests after pre-stretch the {1 0 −1 2} twinning was restrained and the volume fraction of twins decreased, leading to the improvement of yield strength by increasing in pre-stretching levels.
 
Article
The hot tensile deformation and fracture behaviors of the hot-rolled AZ31 magnesium alloy were studied by uniaxial tensile tests with the temperature range of 523–723 K and strain rate range of 0.05–0.0005 s−1. Effects of deformation parameters on the strain hardening rate, strain rate sensitivity, microstructural evolution and fracture morphology were discussed. The results show that: (1) The flow curves show a considerable strain hardening stage and no obvious diffuse necking stage under the relatively low temperatures (523 and 573 K). (2) The elongation to fracture increases with the increase of the deformation temperature. But, the sharp drop of the elongation to fracture under 723 K and 0.0005 s−1 results from the synthetical effects of the grain growth, inverse eutectic melting reaction (α + β = L) and the incipient melting of α matrix. (3) For the case with the deformation temperature of 623 K and relatively low strain rates, the fracture mechanism is the combination of the void coalescence and intergranular fracture. (4) Under the deformation temperature of 723 K, the fine recrystallized grains experienced a rapid growth and the deformation mechanism is the dislocation creep with the help of inverse eutectic liquid phase. (5) The presence of proper amount of liquid phase on the grain boundary changes the deformation mechanisms, and makes great contribution to the high ductility. However, it will deteriorate the material ductility if the amount of liquid phase is too much.
 
Article
The hot tensile deformation behaviors of a typical Al–Cu–Mg alloy are investigated by uniaxial tensile tests with the strain rate range of (0.05–0.001) s−1 and temperature range of (673–748) K. The experimental results show that the true stress–strain curves exhibit a peak stress at a very small strain, after which the flow stresses decrease slowly until fracture, showing an obvious dynamic softening behavior. This hot tensile deformation is a thermally activated process, which indicates the competitions of work hardening, dynamic recovery, dynamic recrystallization, and the initiation and growth of voids or cracks. Considering the coupled effects of forming temperature, strain rate, and strain on the material hardening and softening behavior, a new phenomenological constitutive model is proposed to describe the hot tensile deformation behaviors of the studied Al–Cu–Mg alloy under relatively low strain rates. In the proposed constitutive model, the material constants are expressed as functions of forming temperature and strain rate. A good agreement between the predicted and measured results shows that the proposed model can give an accurate estimate of flow stress for the studied Al–Cu–Mg alloy.
 
Article
Large dimensional bulk nanocrystalline based Fe–Al–Cr alloys with 5, 10 and 15 wt.% Cr which were about 200 mm in diameter and 10 mm in thickness was prepared by an aluminothermic reaction casting method. Microstructures of the alloys were investigated by scanning electron microscope (SEM) attached with energy dispersive spectrometer (EDS) and electron backscattered diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscope (TEM). Compressive properties of the alloys were tested. The results show that the alloys were consisted of a Fe–Al–Cr nanocrystalline matrix with the grain size in a range of 15–18 nm and a precipitated Cr7C3 phase which dispersed homogeneously in the matrix. The content of Cr dissolved in the nanocrystalline matrix, volume fraction and morphology of the Cr7C3 phase varied with the increasing of Cr element added in the alloys. Compressive strength of the alloys was in a range of 1100–1200 MPa. The alloy with 10 wt.% Cr had the highest yield strength of about 1048 MPa, while the alloy with 15 wt.% Cr had the lowest yield strength of about 911 MPa. The alloys showed considerable ductility and best plastic deformation capability for that of 15 wt.% Cr.
 
Article
The effects of post-bond heat treatments on the microstructure and tensile properties of diffusion-bonded Ni-base superalloys, Alloy 617 and Haynes 230, were investigated. In the as-bonded condition, precipitates including carbides and oxides were extensively observed along the bond-line. To remove the precipitates, post-bond heat treatments were applied at temperatures ranging from 1000 to 1200 °C for up to 100 h. In the as-bonded condition, a significant loss of ductility was observed, especially at 900 °C, for both alloys. Also, the final fracture occurred at the bond-line in the form of a brittle fracture in the as-bonded condition. As the post-bond heat treatment temperature was increased, the tensile ductility at 900 °C improved significantly while the strength decreased to a certain extent. The recovery of the tensile ductility was closely related to the dissolution of precipitates during the post-bond heat treatments. Eventually, the tensile ductility of diffusion-bonded Ni-base alloys at 900 °C was increased to half that of the base metal by the post-bond heat treatments.
 
Article
Structure, electrical resistivity, hardness, elastic modulus and roughness of Sn–10%Sb–2%Cu–x%Zn [x = 0.5, 1.0, 1.5, 2.0, 2.5 wt.%] rapidly solidified alloys have been investigated. Investigations have been made by using X-ray diffraction, scanning electron microscope (SEM), double bridge, Vickers hardness tester, the dynamic resonance technique and surface roughness tester. X-ray diffraction showed that, adding different amounts of zinc to the Sn–10%Sb–2%Cu changed its structural properties which affect all measured physical properties. Elastic modulus, hardness and electrical resistivity are increased by increasing the zinc content. Internal friction and roughness are varied. According to our results, the Sn–10%Sb–2%Cu–2.5%Zn alloy has good properties for bearing applications.
 
Article
The development of Arctic oil and gas fields requires low temperature high strength steel materials that can resist critical loads in extreme environments. This paper investigates the mechanical properties such as stress–strain curves, elastic modulus, yield strength, ultimate tensile strength, and fracture strain of normal mild steel and high strength S690 steel to be used in low temperatures relevant to arctic environment. Tensile tests are carried out on steel coupons at different temperatures ranging from −80 °C to +30 °C in a cooling chamber. The influences of the low temperatures on the mechanical properties of mild steel and high strength steel are compared and their differences are discussed. Regression analyses are also carried out on the test data to develop empirical formulae to predict the elastic modulus, yield strength, and ultimate strength of the steels at ambient low temperatures. Finally, design formulae are recommended and their accuracies are further confirmed by the test data including those from the literature.
 
Article
Under extreme thermal cycling delamination initiates and propagates on the interface between top coating and bond coating in thermal barrier coating (TBC) system. The objective of this work is to study the effects of geometrical and material parameters, such as the thicknesses and moduli of top and bond coats, on the interfacial delamination behavior of TBC. The interfacial crack driving force is obtained as functions of the Young’s moduli of top and bond coats, the thicknesses of top coat and bond coat, etc. It is shown that in case of a stiffer top coat deposited on a relatively compliant bond coat the interfacial delamination can emerge more easily since the driving force approaches to an enormous value while emanating from the root of a channel surface crack. It is concluded that interfacial delamination can easily be initiated for a thick, stiff top coat. Considering the thermal barrier and mechanical loading carrying capabilities of coatings, optimal top coat thickness exists for the optimization design of TBC structure.
 
Article
This paper focuses on numerical simulation of impact tests of reinforced concrete (RC) beams by the LS-DYNA finite element (FE) code. In the FE model, the elasto-plastic damage cap (EPDC) model, which is based on continuum damage mechanics in combination with plasticity theory, is used for concrete, and the reinforcement is assumed to be elasto-plastic. The numerical results compares well with the experimental values reported in the literature, in terms of impact force history, mid-span deflection history and crack patterns of RC beams. By comparing the numerical and experimental results, several important behavior of concrete material is investigated, which includes: damage variable to describe the strain softening section of stress–strain curve; the cap surface to describe the plastic volume change; the shape of the meridian and deviatoric plane to describe the yield surface as well as two methods of incorporating rebar into concrete mesh. This study gives a good example of using EPDC model and can be utilized for the development new constitutive models for concrete in future.
 
Article
The high-temperature deformation behaviors of a typical Ni-based superalloy are investigated by hot compression tests under the strain rate of 0.001–1 s−1and temperature of 920–1040 °C. The experimental results show that the deformation behaviors of the studied superalloy are significantly affected by the deformation temperature, strain rate and strain. The flow stress increases with the increase of strain rate or the decrease of deformation temperature. The flow stress firstly increases with the strain to a peak value, showing the obvious work hardening behaviors. Then, the stress decreases with the further straining, indicating the dynamic flow softening behaviors. Considering the coupled effects of deformation temperature, strain rate and strain on the hot deformation behaviors of the studied Ni-based superalloy, the phenomenological constitutive models are established to describe the work hardening-dynamic recovery and dynamic softening behaviors. In the established models, the material constants are expressed as functions of the Zener–Hollomon parameter. The established constitutive models can give good correlations with the experimental results, which confirm an accurate and precise estimation of the flow stress for the studied Ni-based superalloy.
 
Article
An Al–Ni–Y–Co–La metallic glass was laser-melted onto an Al substrate which was at two different temperatures: 25 °C and 250 °C. It was found that the substrate temperature played a critical role in determining the interface bonding between substrate and support and final solidification microstructures. The higher substrate temperature resulted in the formation of a stronger interface bond between metallic glass and substrate while lower substrate temperature resulted in the formation of a weaker interface bond. This has been attributed to different cooling rates and thermal histories present in the two cases. A multi-physics-based computational model based on the heat transfer theory in heat transient mode of COMSOL™ was introduced to explain the underlying mechanism.
 
Article
Compression tests were carried out on ductile cast iron with different sample geometries in order to understand the influence of the stress triaxiality on the local strain. The tests were performed in dry friction conditions involving a complex local stress and strain state with a severe barrelling. The numerical simulation of the compression tests was achieved by using finite element analysis. Local strain was evaluated using microstructural quantifications. A relationship between the nodule strain, experimentally determined at different stress–strain stages, and the numerical simulation is proposed. The numerical predictions agree with the distribution of the experimental aspect ratio defined as the ratio between the major and minor axis of the graphite nodules. This study shows that the nodule strain is a good indicator of the total material strain at room temperature for different triaxiality states and complex strains. In addition, it was highlighted that graphite nodules cannot always be considered as ordinary voids during the plastic strain process.
 
Article
Solid-state ultrasonic spot welding (USW) was used to join Al/Mg/Al tri-layered clad sheets, aiming at exploring weldability and identifying failure mode in relation to the welding energy. It was observed that the application of a low welding energy of 100 J was able to achieve the optimal welding condition during USW at a very short welding time of 0.1 s for the tri-layered clad sheets. The optimal lap shear failure load obtained was equivalent to that of the as-received Al/Mg/Al tri-layered clad sheets. With increasing welding energy, the lap shear failure load initially increased and then decreased after reaching a maximum value. At a welding energy of 25 J, failure occurred in the mode of interfacial failure along the center Al/Al weld interface due to insufficient bonding. At a welding energy of 50 J, 75 J and 100 J, failure was also characterized by the interfacial failure mode, but it occurred along the Al/Mg clad interface rather than the center Al/Al weld interface, suggesting stronger bonding of the Al/Al weld interface than that of the Al/Mg clad interface. The overall weld strength of the Al/Mg/Al tri-layered clad sheets was thus governed by the Al/Mg clad interface strength. At a welding energy of 125 J and 150 J, thinning of weld nugget and extensive deformation at the edge of welding tip caused failure at the edge of nugget region, leading to a lower lap shear failure load.
 
Article
The main objective of the present study is to assess the environmental advantages of substituting aluminium for a polymer composite in the manufacture of a structural product (a frame to be used as a support for solar panels). The composite was made of polypropylene and a recycled tyres’ rubber granulate. Analysis of different composite formulations was performed, to assess the variation of the environmental impact with the percentage of rubber granulate incorporation. The results demonstrate that the decision on which of the two systems (aluminium or composite) has the best life cycle performance is strongly dependent on the End-of Life (EoL) stage of the composite frame. When the EoL is deposition in a landfill, the aluminium frame performs globally better than its composite counterpart. However, when it is incineration with energy recovery or recycling, the composite frame is environmentally preferable. The raw material production stage was found to be responsible for most of the impacts in the two frame systems. In that context, it was shown that various benefits can accrue in several environmental impact categories by recycling rubber tyres and using the resulting materials. This is in a significant part also due to the recycling of the steel in the tyres. The present work illustrates how it is possible to minimize the overall environmental impact of consumer products through the adequate selection of their constitutive materials in the design stage. Additionally it demonstrates how an adequate EoL planning can be an important issue when developing a sustainable product, since it can highly influence its overall life cycle performance.
 
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The main goal of this study is optimization of residual stresses produced by friction stir welding (FSW) of 5086 aluminum plates. Taguchi method is employed as statistical design of experiment (DOE) to optimize welding parameters including feed rate, rotational speed, pin diameter and shoulder diameter. The optimization process depends on effect of the welding parameters on longitudinal residual stress, which is measured by employing ultrasonic technique. The ultrasonic measurement method is based on acoustoelasticity law, which describes the relation between acoustic waves and internal stresses of the material. In this study, the ultrasonic stress measurement is fulfilled by using longitudinal critically refracted (LCR) waves which are longitudinal ultrasonic waves propagated parallel to the surface within an effective depth. The ultrasonic stress measurement results are also verified by employing the hole-drilling standard technique. By using statistical analysis of variance (ANOVA), it has been concluded that the most significant effect on the longitudinal residual stress peak is related to the feed rate while the pin and shoulder diameter have no dominant effect. The rotational speed variation leads to changing the welding heat input which affects on the residual stress considerably.
 
Article
Monoclinic (La0.95 − xBixEu0.05)PO4 nanowires with lengths of ~ 1.5 μm and diameters of ~ 20–50 nm (aspect ratio up to the high value ~ 75) have been synthesized via hydrothermal crystallization in the presence of sodium tartrate (Tar2 −). Detailed characterizations of the materials were achieved by the combined techniques of XRD, FE-SEM, TEM, FT-IR, and optical spectroscopies, and the formation mechanism of the nanowires was expatiated. It was found that Tar2 − as a shape modifier can cap the growth of {012} facets and thus led to nanowires of high [001] orientation. The effects of experimental parameters such as Tar2 −/M3 + (M = total cation) and PO43 −/M3 + molar ratios, hydrothermal temperature and reaction time on phase and morphology evolution of the nanowires were unveiled. The effects of shape anisotropy, calcination and Bi3 + doping on the photoluminescence properties of the (La0.95 − xBixEu0.05)PO4 nanowire phosphors were also investigated in detail, including excitation, emission, fluorescence lifetime, and CIE chromaticity coordinates. The optimal Bi3 + content was determined to be ~ 0.7 at%.
 
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This paper elucidated the effects of the Bi element (0 wt%, 0.5 wt% and 1.5 wt%) on the microstructure, electrical, wettability and mechanical properties of the Sn-0.7Cu-0.05Ni as a high strength solder. Besides using the conventional cross-sectioned microstructure image, the real-time synchrotron radiation imaging and synchrotron micro-X-ray fluorescence (XRF) technique was also used to investigate the microstructure, focusing on the in-situ growth behaviour of the primary (Cu,Ni)6Sn5 intermetallic and elemental distribution that had occurred in the Sn-0.7Cu-0.05Ni-1.5Bi. Other essential properties of solder material, such as wettability, electrical resistance, and shear strength, were also determined. The results showed that the addition of 1.5 wt% Bi refined the primary (Cu,Ni)6Sn5 intermetallics formation in the solder joint, where it grew earlier and faster relative to that in the Sn-0.7Cu-0.05Ni/Cu joint. Additionally, the addition of 1.5 wt% Bi resulted with a 3% reduction of its electrical resistance while increasing the wettability of the solder alloy. 1.5 wt% addition of the Bi element also found to have contributed to a significant increment of shear strength relative to that of the Sn-0.7Cu-0.05Ni. The results confirmed that the developed material is applicable as a potential high strength solder material in the context of advanced interconnecting applications. Keywords: Soldering, Solder, Interconnects, Intermetallics, Solid solution, Microstructure, Solder properties
 
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An investigation of the coexistent ferroelectric phase was carried out on the ternary system of 0.87BaTiO3–(0.13-x)BaZrO3–xCaTiO3 [abbreviated as BT–BZ–xCT (where 0.00 ≤ x ≤ 0.13)]. Temperature-, frequency-dependent dielectric data, electric field-dependent strain and polarization as a function of composition are presented in order to understand the relationships of structure-properties and find the high piezoelectric response in this system. Results showed that ceramics in the composition range of 0.00 ≤ x < 0.04 were of a rhombohedral structure and transformed into a tetragonal structure at x > 0.06. The multiphase coexistence of the rhombohedral and tetragonal phase in this system was identified at x = 0.06. A large, virtually hysteresis-free electric field induced strain of 0.23% was achieved with the composition, x = 0.06, at 40 kV/cm on the boundary between rhombohedral and tetragonal phase. This relates to an extraordinarily high and normalized piezoelectric coefficient (Smax/Emax) of 1280 pm/V, which was reached at a low electric field applied at 10 kV/mm. These results indicated that a high piezoelectric response may stem primarily from the rhombohedral-tetragonal phase boundary, due to greater lattice softening and reduced energy barriers for polarized rotation.
 
Article
(Na0.85K0.15)0.5Bi0.5TiO3 (NKBT) multilayer thin films with different thicknesses of 100–700 nm, corresponding to 2–14 layers with each layer of ~50 nm thickness, are synthesized on Pt(111)/Ti/SiO2/Si substrates to form Pt/NKBT/Pt/Ti/SiO2/Si heterostructures using different spin-coating and annealing conditions in a modified aqueous sol-gel process. The multilayer thin films spin-coated by two steps (step 1/2) at 600/4000 rpm for 6/30 s and annealed at 700 °C for 5 min with a heating rate of 30 °C/s show a dense, uniform, and continuous morphology as well as a pure perovskite structure with a rhombohedral–tetragonal phase transition at ~140 °C and no preferential orientation in the heterostructures. Their structural and electromechanical properties exhibit consistent improvement trends with increasing thickness from 100 to 550 nm (i.e., 2–11 layers). The 550 nm-thick, 11-layer films demonstrate the best ferroelectric, dielectric, piezoelectric, and electric performance in terms of the highest remnant polarization, saturation polarization, dielectric constant, and effective piezoelectric constant of 18.3 μC/cm², 53.6 μC/cm², 463, and 64 pm/V, as well as the lowest coercive field, dielectric loss tangent, and leakage current density of 116 kV/cm, 0.057, and 27 μA/cm², respectively. The observed thickness-dependent improvement is explained by an interfacial passive layer effect where the motion of both 180° and non-180° domain walls is enhanced in the thicker multilayer thin films by weakening the influence of domain pinning in the interfacial passive layers between the multilayer thin films and the substrates.
 
(a) XRD patterns of Na 3 V 2 (PO 4 ) 3 /C & Na 3 V 2-x Fe x (PO 4 ) 3 /C + rGO (x = 0, 0.05, 0.10, and 0.15), (b) crystal structure of Na 3 V 2-x Fe x (PO 4 ) 3 at different orientations, (c) and (d) XRD spectra and Rietveld refinement results of Na 3 V 2 (PO 4 ) 3 /C and Na 3 V 1.90 Fe 0.10 (PO 4 ) 3 /C + rGO, and (e) the Rietveld refined cell parameters in the R-3c space group for Na 3 V 2-x Fe x (PO 4 ) 3 (0 ≤ x ≤ 0.15).
SEM images of (a) NVP/C, (b) Fe0.05-NVP/C + rGO, (c) Fe0.10-NVP/C + rGO, (d) Fe0.15-NVP/C + rGO, (e) TEM images of NVP/C, and (f) and (g) TEM images of Fe0.10-NVP/C + rGO.
(a) and (b) XPS spectra of V2p and Fe2p of Na 3 V 2-x Fe x (PO 4 ) 3 /C + rGO (x = 0.05, 0.10, and 0.15), and (c) TGA curves of Na 3 V 2-x Fe x (PO 4 ) 3 /C + rGO (x = 0.05, 0.10, and 0.15).
(a) The cyclic voltammetry of Na 3 V 2 (PO 4 ) 3 /C at a sweeping rate of 0.05 mVs −1 , (b) galvanostatic cycling profiles of Fe0.10-NVP/C + rGO at different current rate, (c) rate performance of Na 3 V 2 (PO 4 ) 3 /C & Na 3 V 2-x Fe x (PO 4 ) 3 /C + rGO (x = 0, 0.05, 0.10, and 0.15), and (d) cycle testing of Na 3 V 2 (PO 4 ) 3 /C & Na 3 V 2-x Fe x (PO 4 ) 3 /C + rGO (x = 0, 0.05, 0.10, and 0.15) at a current density of 20C.
(a) Nyquist impedance plots of Na 3 V 2 (PO 4 ) 3 /C & Na 3 V 2-x Fe x (PO 4 ) 3 /C + rGO (x = 0, 0.05, 0.10, and 0.15) with insertion of the equivalent circuit, (b) cyclic voltammetry of Na 3 V 2 (PO 4 ) 3 /C & Na 3 V 2-x Fe x (PO 4 ) 3 /C + rGO (x = 0, 0.05, 0.10, and 0.15) at a current density of 0.1C, (c) The potentiostatic plot of NVP/C and Fe doped NVP/C-rGO pellets with 10 mm in diameter and ~0.80 mm in thickness, the applied DC voltage is 0.5 V.
Article
Due to its high theoretical capacity and stable structure, Na3V2(PO4)3 has gained much attention as a potential cathode for sodium-ion batteries (SIBs) in large-scale energy storage applications. However, poor electronic conductivity usually results in the low rate capacity and poor cyclability, limiting its application. Herein, we successfully introduce Fe3+ to substitute V3+ through doping engineering. Compared with Na3V2(PO4)3/C, an excellent initial high-rate capacity of 91.2 mAhg−1 (77.5% of the theoretical capacity) at 20 C (2.35 A g−1) has been achieved in Na3V1.9Fe0.1(PO4)3/C + rGO due to the improved electronic conductivity introduced by Fe doping and rGO modification, and a stable cyclability with 88.7% capacity retention after 100 charge/discharging cycles, implying the perfect structural stability of the composites. It is expected that the results obtained will grasp new insights into designing the optimal cathode and realizing the commercial synthesis for the large-scale rechargeable sodium energy storage devices.
 
Article
The cast Mg-4Zn-0.5Ca-0.16Mn (wt%) alloy, prepared through conventional melting-casting route, exhibits appreciable strength (UTS~180 MPa, YS~175 MPa) with limited elongation (<1%). As the cast specimens are subjected to homogenization treatments for 6–72 h at 633 K, the yield strength decreases by an acceptable margin (97–117 MPa) accompanied by a noteworthy increase in ductility (3.2–8.5%). The improvement in ductility is primarily due to the dissolution of the coarse networks of the eutectic Ca2Mg6Zn3 phase formed during casting. Interestingly, the work hardening response of the alloy also improves with homogenization. The evolution of grain size heterogeneity, the presence of Mn particles and the evolution of β1′ precipitates have been identified as the major contributing factors behind this. The β1′ precipitates predominantly form at the interface of the Mn particles/Mg matrix and evolve by changing the aspect ratio during homogenization treatment. This evolution of β1′ precipitates is accountable for the age-hardening kind of response of the alloy where the three conditions, namely under-aging, peak-aging, and over-aging, can be distinguished clearly in terms of hardness and strength. The homogenization duration of 24 h has been identified to generate a better combination of strength, ductility and work hardening response in the studied alloy.
 
Article
Additive manufacturing Al-Mg-Sc-Zr alloys offer significant advantages for lightweight application with complex shapes. The paper systematically investigated the effects of aging treatment on microstructural evolution and mechanical properties of SLM printed Al-3.02Mg-0.2Sc-0.1Zr alloy. The SLM printed sample with a relative density of 99.2% was achieved at an optimal laser parameters. After aging, the hardness was improved from initial 85 HV of as-printed sample to 120 HV. The strength and ductility trade-off of the printed sample can be tailored by regulating aging parameters; the maximal tensile strength of 400 MPa and yield strength of 327 MPa can be obtained at an optimal aging parameters. The XRD patterns show the secondary peak of Al 3 (Sc,Zr) after aging treatment due to Al 3 (Sc,Zr) particles separation from the α-Al matrix and the diffraction angles shifts to a higher value owing to the release of residual stress. Moreover, Nano-sized Al 3 (Sc,Zr) precipitates on the grains boundaries hamper grain growth, which was responsible for the grain sizes maintaining after aging treatment.
 
Article
Ferroelectric semiconductors splitting water reactions have presented a new paradigm in improving conversion efficient of solar energy into electricity or fuel. Here, we show the switchable photoelectrochemical response controlled by ferroelectric polarization in (101)-oriented Pb(Zr0.2Ti0.8)O3 (PZT) epitaxial films prepared on the (110) SrTiO3 substrate with SrRuO3 as bottom electrodes. Photoelectrochemical (PEC) measurements exhibit that the switchable photocurrent response can be observed in the PZT/SRO heterostructures photo-electrode. Moreover, under illumination, the switchable photocurrents of the PZT/SRO electrode present high repeatability and non-volatility, which only depend in the ferroelectric polarization direction of the PZT film. The result indicates that the PZT/SRO electrode may be as a photoanode or photocathode only through poling treatment with the external electric field. We suggest that the internal electric field and depletion region by ferroelectric polarization at the PZT film is mainly responsible for the switchable PEC effect. The study indicates that this ferroelectric photo-electrode material may have potential applications in solar water splitting, and specially in the PEC sensing and any other smart photo-responsive systems.
 
Top-cited authors
Y.C. Lin
  • Central South University
Chen Xiao-Min
  • Changsha University of Science and Technology
J. Wei
  • Singapore Institute of Manufacturing Technology (SIMTech)
Roland E. Logé
  • École Polytechnique Fédérale de Lausanne
Yung Shin
  • Purdue University