Quasi-static Uniaxial Tensile Research Articles

Microstructural investigation and mechanical behavior of a two-material component fabricated through selective laser melting of AlSi10Mg on an Al-Cu-Ni-Fe-Mg cast alloy substrate

A hybrid-part made of two materials was fabricated by selective laser melting (SLM) of AlSi10Mg on an Al-Cu-Ni-Fe-Mg cast alloy substrate. The microstructure of the two-material component and the interface is investigated using multi-scale characterization techniques including optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The microstructure of SLM-AlSi10Mg consists of fine cellular dendrites and columnar grains, developed along the building direction, where the substrate cast alloy is featured by large equiaxed grains. OM and SEM studies of the interface show a sound metallurgical bonding as a result of the melting of AlSi10Mg powder and partial melting of the cast substrate assisted by the circulate flows and Marangoni convection. The circulate flows cause complex phenomena at the interface, which lead to the dilution of alloying elements and a variation in the microstructure of the first consolidated layer of SLM-AlSi10Mg (as a result of variation in thermal gradient and solidification rate). TEM investigations of the interface reveal segregation of alloying elements at the interdendritic regions after solidification. Moreover, no precipitate is formed on top of the interface, due to the rapid solidification and dilution of the alloying elements. EBSD analysis of the interface shows substantial differences in the grain structure of SLM-AlSi10Mg and the cast substrate, in terms of size and morphology. Mechanical properties of the hybrid material are studied afterwards using Vickers microhardness measurements, nanoindentation and quasi-static uniaxial tensile tests. The SLM-AlSi10Mg side of the hybrid-part possesses better performance, mainly due to its finer and hierarchical microstructure.

Study of Fracture Mechanism of Machinable Mica Glass-Ceramics under Quasi-Static Conditions

In order to study the deformation and fracture mechanism of machinable mica glass ceramics under different loading modes, quasi-static uniaxial tensile and compression experiments are designed and analyzed based on the obtained quasi-static stress-strain curves at different strain rates, the macroscopic and microscopic fracture morphology of the samples and the nano-indentation experiment. The results show that mica glass ceramics are basically elastic brittle bodies. A very short “softening” section before the compression fracture is observed. There is a significant SD (tensile and compressive strength difference) effect, and the ratio of compressive to tensile strength is 14. The fracture mechanism of mica glass ceramics is related to the loading mode. The fracture mechanism is normal tensile fracture perpendicular to the loading axis under tensile loading. Under compressive loading, there is a mixed mode of distensile splitting and local shear failure. The microcrack is preferentially nucleated and extends to the weak interface at the junction of two phases, and the critical nucleation load is about 20 mN. The energy consumption mechanism of crack initiation and propagation at the weak interface and cleavage steps are the reason for the softening of the compression end curve.

A microstructurally inspired constitutive model for skin mechanics.

This study investigates the link between the mechanical properties of skin and its microstructural characteristics. Rat back skin samples from different locations, orientations, and sexes were collected and subjected to quasi-static uniaxial tensile tests. Stress-stretch behavior at low stress ranges and rupture data at high stress ranges were collected. The influence of location, orientation, and sex on skin mechanical properties was examined by comparing the mechanical parameters (i.e., initial slope, maximum slope, ultimate tensile strength, rupture stretch, and toughness) evaluated from the tensile testing data. Location and orientation were both found to have a significant effect on the mechanical properties. Collagen structural data (i.e., fiber orientation distribution, relative content, and fiber straightness) were evaluated using histology images. It was found that the rat lower (caudal) back had higher relative collagen content when compared to the upper (cranial) back. A microstructurally based constitutive model was proposed to describe the mechanical behavior of preconditioned rat back skin. The constitutive model incorporated the distribution of collagen fiber bundle orientations and relative collagen content measured from histology, and showed good agreement with the tensile test data. The influence of location and orientation was also evident in the optimized constitutive parameters. This study was a comprehensive investigation that combines skin mechanical behavior, micro-structure, and constitutive modeling.

Electro-mechanical characterization of three-dimensionally conductive graphite/epoxy composites under tensile and shear loading

Abstract An experimental study was performed to compare the electro-mechanical response of three-dimensionally conductive woven carbon fiber/epoxy laminated composites under quasi-static uniaxial tensile and in-plane shear loading conditions. Three-dimensional (3D) electrical network was generated in these composites by embedding carbon nanotubes (CNTs) of 0.025 wt% in the epoxy and reinforcing short carbon fibers (150 μm and 350 μm long) with a fiber density of 1000 fibers/mm2 between the laminates using electro-flocking process. CNTs are effectively dispersed in the epoxy matrix using a combination of ultrasonication and shear mixing techniques. A compression molding fabrication technique was employed to fabricate composite materials. For all composite types, in general, the in-situ electrical response showed a trend of initial decrease in resistance and later increase in resistance for tensile loading. However, no noticeable increase in electrical resistance was observed until failure of the composite under shear loading conditions. Both CNTs and short carbon fibers made new contacts with neighboring carbon fiber laminates for entire duration of shear loading even though the composite was undergoing progressive failure.

Experimentation of the Bilinear Elastic Behavior of Plain-Woven GFRP Composite with Embedded SMA Wires.

In this paper, a plain-woven glass-fabric-reinforced polymer (GFRP) composite with embedded shape memory alloy (SMA) wires is investigated by means of experiments. The vacuum-assisted resin injection (VARI) method is utilized to fabricate the composite specimens. Quasi-static uniaxial tensile tests are then carried out to evaluate the influence of SMA reinforcement on the stress–strain behavior of the composite. Only the elastic behavior of the composite is considered in the present study. The tensile strain in all the experiments is kept below 2.5% to avoid debonding of the SMA-resin interface, which would lead to failure of the composite. Stress–strain curves are obtained and shown to present a bilinear behavior due to phase transformation taking place in the SMA wires beyond a certain stress threshold.

A stereological ubiquitiformal softening model for concrete

A stereological ubiquitiformal softening model for describing the softening behavior of con- crete under quasi-static uniaxial tensile loadings is presented in this paper. In the model, both the damage evaluation process of fracture cross-sections and their distribution along the specimens axis are taken into account. The numerical results of a certain kind of full grade concrete made of crushed coarse aggregate are found to be in good agreement with the experimental data. Moreover, an experiental relation between the lower bound to the scale invariance of concrete and its tensile strength is also obtained by data fitting of the experimental data, which provides an effective approach to determine the lower bound to scale invariance of concrete.

Fiber-reinforced polymer composites test specimen design for selected damage mechanisms

Fiber-reinforced polymer composites yield a range of microscopic damage mechanisms even under apparently “simple” load cases, e.g. quasi-static uniaxial tensile tests to failure. Even reducing the fiber-reinforced polymer composite to a single fiber embedded in a matrix will produce several different damage types under quasi-static tensile loading. These are fiber breaks and simultaneous fiber–matrix debonding as well as friction between fiber and debonded matrix, and sometimes, additional matrix cracks. Acoustic emission monitoring of mechanical load tests on material specimens or components is often used to identify the occurrence of damage and attempts at locating the source and identifying the damage mechanism or type in a wide range of materials. The complex damage behavior of fiber-reinforced polymer composites poses a challenge in that respect. Therefore, various approaches (e.g. pattern recognition or neural networks) have been developed to identify the different microscopic damage mechanisms from acoustic emission signals obtained from various load tests. For improved understanding of the damage mechanisms in fiber-reinforced polymer composites as well as for validating the procedures for identifying the types of mechanisms, fiber-reinforced polymer specimens showing a “single dominant damage mechanism”, i.e. occurring in significantly larger number than all others, at least in certain stages of damage accumulation or in localized volume elements, can be designed. The contribution discusses and classifies selected examples of single dominant damage mechanism for fiber-reinforced polymer composites and their application.

Investigation of the fracture behaviors of windshield laminated glass used in high-speed trains

The objective of this study is to investigate the fracture behaviors of windshield laminated glass for high-speed trains. For this purpose, tempered glass specimens sampled from constituent components of polyvinyl butyral (PVB) laminated windshield panes were tested using the following tests: flexural strength test, quasi-static uniaxial tensile test, low strain rate compression test and dynamic compressive test with split Hopkinson pressure bar (SHPB). Together with simulations, the testing results were used to determine the constitutive constants of the Johnson-Holmquist ceramic (JHC) model, including the equation of state, the strength criterion and the strain-rate effect. To validate the JHC model, it is used to simulate a safety hammer impact test on PVB-Laminated tempered glass (PVB-LTG). The simulation results showed that the JHC model with tempered material constants for PVB-LTG successfully predicted the impact response of windshields. The practical implications of fragmentation and cracking are also discussed.

Strengthening mechanisms in direct metal laser sintered AlSi10Mg: Comparison between virgin and recycled powders

Rod shaped samples of AlSi10Mg additively manufactured using recycled powder through direct metal laser sintering (DMLS) process showed higher quasi-static uniaxial tensile strength in both horizontal and vertical build directions than those of cast counterpart alloy. In addition, they offered mechanical properties within the range of other additively manufactured counterparts. TEM showed that the microstructure of the as-built samples comprised of cell-like structures featured by dislocation networks and Si precipitates. HRTEM studies revealed the semi-coherency characteristics of the Si precipitates. After deformation, the dislocation density increased as a result of generation of new dislocations due to dislocation motion. The dislocations bypassed the precipitates by bowing around them and penetrating the semi-coherent precipitates. Strengthening of recycled DMLS-AlSi10Mg alloys manufactured in both directions was attributed to Orowan mechanism (due to existence of Si precipitates), Hall-Petch effect (due to eutectic cell walls), and dislocation hardening (due to pre-existing dislocation networks). Due to the slightly different microstructure, the contribution of each strengthening mechanism was slightly different in identical samples made with virgin powder.

An investigation of in-plane tensile properties of re-entrant chiral auxetic structure

A new auxetic structure, re-entrant chiral auxetic (RCA) structure, is proposed for the first time in this paper. The RCA structure combines the topological features of hexagonal re-entrant and anti-tetrachiral honeycombs. Additive manufacturing technique, stereolithography (SLA), and traditional waterjet machining (WJM) were employed to fabricate six samples made from photopolymer (VisiJet SL Flex) and aluminum alloy (6061), respectively. Quasi-static uniaxial tensile tests were conducted in the X and Y directions, respectively. Numerical models were developed using ANSYS/LS-DYNA and verified by experimental data. Deformation modes, stress–strain curves, and Poisson’s ratios were considered to examine the effects of loading directions and material types. A comparative study was conducted experimentally and numerically between the well-known hexagonal re-entrant honeycomb, and this newly developed RCA structure. The proposed RCA structure presented here was found to display lower density compared with re-entrant honeycomb. Moreover, it shows higher tensile properties and auxetic effect compared with re-entrant honeycomb when loaded in the X direction. The validated FEA models were employed to investigate the effect of friction on the deformation pattern and mechanical properties of the RCA structure when it is loaded in both directions.

Effects of different types of twinning on microstructure and mechanical properties of a strongly textured TA2 commercially pure titanium alloy subjected to rolling at ambient and cryogenic temperatures

Strongly textured commercially pure titanium alloy TA2 plates with different initial textures have been rolled at cryogenic and ambient temperatures to 4% reduction and then post-annealed at 50 °C for 12 h. Microstructures of the samples were investigated using electron backscatter diffraction. The mechanical property of the sheets was tested via quasi-static uniaxial tensile tests along the rolling direction at room temperature. The effects of initial texture and rolling temperature on twin activity and mechanical property have been investigated. Twinning is very active in TA2 titanium during rolling at either room or cryogenic temperature. $$\{ 11\overline{2} 2\}$$ contraction twins can be observed in all the sheets and are the dominant twin mode for the sheets with an initial texture having c-axes parallel to the normal direction (ND). Extension twins have rarely been seen in sheets having an initial texture with c-axes parallel to ND, but play quite an important role in the sheets having an initial texture with c-axes perpendicular to ND. The initial texture of the sheet is considered to determine the twin mode while the cryogenic rolling temperature is found to increase the numbers of twins. Post-annealing does not change obviously the rolled microstructure. After annealing, the strength decreases and elongation to fracture slightly increases. The cryorolled sample has the better strength with little loss in elongation, and this mechanical enhancement is attributed to massive twinning.

Selective Laser Melting Produced Ti-6Al-4V: Post-Process Heat Treatments to Achieve Superior Tensile Properties.

Current post-process heat treatments applied to selective laser melting produced Ti-6Al-4V do not achieve the same microstructure and therefore superior tensile behaviour of thermomechanical processed wrought Ti-6Al-4V. Due to the growing demand for selective laser melting produced parts in industry, research and development towards improved mechanical properties is ongoing. This study is aimed at developing post-process annealing strategies to improve tensile behaviour of selective laser melting produced Ti-6Al-4V parts. Optical and electron microscopy was used to study α grain morphology as a function of annealing temperature, hold time and cooling rate. Quasi-static uniaxial tensile tests were used to measure tensile behaviour of different annealed parts. It was found that elongated α’/α grains can be fragmented into equiaxial grains through applying a high temperature annealing strategy. It is shown that bi-modal microstructures achieve a superior tensile ductility to current heat treated selective laser melting produced Ti-6Al-4V samples.

Large deformation of an auxetic structure in tension: Experiments and finite element analysis

The present paper reports on the post-yield behaviors of an auxetic structure, honeycomb with representative re-entrant topology. Specimens were made of stainless steel and polymer, respectively. Quasi-static uniaxial tensile tests were conducted in the two principal directions, followed by simulations using the commercial code – ABAQUS 6.11-2. The deformation, tensile stress-strain curves and Poisson’s ratio were of interest. A good agreement was observed between the numerical simulations and the experimental results. Subsequently, the effect of cell wall thickness and initial cell angle was studied by means of finite element analysis. An analytical equation was also given for the yield stress of such materials under tension.

Experiment research on rate-dependent constitutive model of Q420 steel

The strain rate effect on the progressive collapse resistance of steel structures under abnormal events or impulsive loading should not be neglected because the constitutive properties of steels change significantly with the loading time. The rate-dependent constitutive properties of Q420, which is a low-alloy high strength structural steel in China, are different with those of the low carbon steel Q235 and the low alloy steel Q345 because of the different manufacturing techniques and micro alloying elements. Quasi-static and dynamic uniaxial tensile tests within the range of 0.001–288s−1 strain rates were carried out to study the rate-dependent mechanical properties of Q420 steel by INSTRON and Zwick/Roell HTM5020 testing machine. Three dimensional finite element (FE) models are developed to predict the true stress-strain relationships of Q420 steel beyond necking under different strain rates by a hybrid experimental-numerical method. The Cowper-Symonds model is verified to be capable of describing the dynamic behavior of Q420 steel at the lower strain rates. The modified H/V-R model established by introducing the dynamic increase factor of Cowper-Symonds model into the H/V-R constitutive model is better to predict the strain rate effect of Q420 steel than the H/V-R model.

Comparison of mechanical characteristics of focused ion beam fabricated silicon nanowires

In this study, we investigate the effects of focused ion beam (FIB)-induced damage and specimen size on the mechanical properties of Si nanowires (NWs) by a microelectromechanical system (MEMS)-based tensile testing technique. By an FIB fabrication technique, three types of Si NWs, which are as-FIB-fabricated, annealed, and FIB-implanted NWs, are prepared. A sacrificial-oxidized NW is also prepared to compare the mechanical properties of these FIB-based NWs. The quasi-static uniaxial tensile tests of all the NWs are conducted by scanning electron microscopy (SEM). The fabrication process and specimen size dependences on Young’s modulus and fracture strength are observed. Annealing is effective for improving the Young’s modulus of the FIB-damaged Si. Transmission electron microscopy (TEM) suggests that the mechanism behind the process dependence on the mechanical characteristics is related to the crystallinity of the FIB-damaged portion.

Experimental investigation of tensile properties and anisotropy of 1420, 8090 and 2060 Al-Li alloys sheet undergoing different strain rates and fibre orientation: a comparative study

Abstract Al-Li alloys have gained great attention for military, aerospace, and commercial applications because of their outstanding properties compared to commercial Al alloys. However, the tensile properties of former Al-Li alloys cannot fulfil most of the design and manufacturing characteristics because of their poor formability, and anisotropy in tensile properties. Therefore, the third generation of Al-Li alloys was developed to overcome the shortcoming of the former Al-Li alloys. The sensitivity of tensile properties and anisotropy behavior of Al-Li alloys to fibre orientation (sample orientation) and strain rate is vitally important from the aspects of formability improvements and developing material models for formability prediction. Therefore, this paper aims at investigating the influence of sample orientation and strain rates on the tensile properties and anisotropy behavior of Al-Li alloys sheet through quasi-static and dynamic uniaxial tensile tests. AA1420 and AA8090 sheets were selected from first and second generations of Al-Li alloys respectively because of their outstanding properties. Moreover, AA2060 is a new third generation Al-Li alloy launched at 2011 by Alcao Inc. The results showed that AA2060 alloy offers superior tensile properties compared with former Al-Li alloys, notably along the rolling direction and at high rates of deformation. For instance, the elongation to fracture of AA2060 was increased to 21.9 % at a strain rate of 2000 s-1. However, it’s formability at room temperature and quasi-static strain rate is very poor. Additionally, AA2060 is still suffering from anisotropic tensile properties, but the degree of anisotropy in less than the former Al-Li alloy. It is concluded that the quasi-static and dynamic tensile properties and formability for Al-Li alloy sheets show a dependable tendency in reference to sample orientation and don’t display the constant trend with the increasing of the strain rate.

Al-Mg合金に対するインデンテーションの荷重変動に及ぼすひずみ速度の影響

Indentation tests are used to determine the local mechanical properties of materials. Previously, the indentation strain rate was correlated with the strain rate in uniaxial tests based on the hardness, which was the obtained load divided by the cross-sectional area. However, the hardness can be influenced by pile-up of material after indentation. The purpose of this study was to relate the indentation strain rate with the uniaxial strain rate through serration behavior. The material used in this study was 5082 aluminum alloy, whose main alloying elements are aluminum and magnesium, and which is known to exhibit serration at certain temperatures and strain rates. Quasi-static uniaxial tensile tests were performed at strain rates from 10-4 to 10-1 s-1 at room temperature. Micro-indentation using a Berkovich indenter was performed at constant loading rates from 0.7 to 350 mN/s. The loading curvature, which was defined as the load divided by the square of the displacement, was used instead of the hardness to avoid the pile-up effect. As a result, the serrated loading curvature in the indentation tests was obtained as the decreasing loading rate. The effective strain rate, which was defined as the derivative of the load with respect to time divided by two times the applied load, decreased with increasing displacement. The serrated loading curvature changed its behavior as the effective strain rate decreased. It behaved similarly to the serration observed in uniaxial tensile tests. It was found that the indentation strain rate is correlated with the strain rate in uniaxial tensile tests through the serration behavior.

Influences of Specimen Size and Temperature on Viscoelastic Tensile Properties of SU-8 Photoresist Films

In this paper, the influences of specimen size and test temperature on the viscoelastic properties of SU-8 photoresist films are described. Films with the thicknesses of 1 μm and 10 μm are subjected to quasi-static uniaxial tensile tests and stress relaxation tests at temperatures ranging from 293 K to 473 K. The average glassy modulus at 293 K is 3.2 GPa, which decreases with an increase in the test temperature irrespective of specimen size. The mean fracture strain depends on film thickness as well as temperature. The fracture strain of the 1-μm thick films is approximately half of that of the 10-μm thick films at each temperature. Stress relaxation tests are conducted for constructing the master curves of the relaxation moduli. There is no apparent thickness dependence on the master curve. Above glass transition temperature, Tg, apparent activation energies for the two films are almost identical, whereas the activation energy for the thinner films is smaller than that for the thicker films below Tg. This size effect is discussed using Fourier transform infrared spectroscopy (FTIR).

Влияние структуры на сопротивление пластической деформации алюминиевого сплава 1560 после обработки методом прессования рифлением

In present work the effect of structural changes in the samples, made of 1560 aluminum alloy rolled sheet products of 1.5 mm in thickness, as a result of groove pressing treatment was investigated. The mechanical properties of the material in the as-received condition and after severe plastic deformation are investigated experimentally in a quasi-static uniaxial tensile tests at a strain rate of 1 s^-1. Microhardness of aluminum alloy 1560 as-received condition samples and groove pressed samples was measured by Vickers method. The changes of microhardness rolled sheet 1.5 mm in thickness after groove pressing were determined. It was found that after four treatment cycles rolled alloy sheet, yield strength and fracture resistance was increased in 1.4 and 1.5 times, respectively, and microhardness value increased in ~ 2.7 times. It was found that the hardening of the investigated alloy is accompanied by decrease ultimate strain to failure of 20%. Analysis of results of changes in 1560 aluminum alloy grain structure after groove pressing treatment, conducted by electron backscatter diffraction was presented. The results obtained in present work confirmed with data obtained in previous studies on the impact of severe plastic deformation on the grain structure and mechanical properties of aluminum alloy 1560.

J2210101 Auボンディングワイヤの機械物性に及ぼすアニールの影響

In this paper, the influence of vacuum annealing on the mechanical properties of gold (Au) bonding wires is described. Au bonding wires with the diameter of 25μm are subjected to quasi-static uniaxial tensile tests at laboratory air. The bonding wire specimens are prepared by the attachment of a wire to a silicon (Si) frame fabricated by deep reactive ion etching (DRIE). The Young's modulus and 0.2% offset yield strangth are 113GPa and 310MPa on average. By annealing at 100〜300℃ for 10min in vacuum, the Young's modulus value gradually decreases with increasing annealing temperature, whereas the yield strangth value drastically drops in the annealed wires at over 200℃. The annealing effect is discussed in the light of a change in the number of recrystallized grains in the wires.