Quasi-static Uniaxial Tensile Tests Research Articles

Temperature-Dependent Macroscopic Mechanical Behaviors and Their Microscopic Explanations in a Medium Mn Steel

Plastic instability (e.g., Luders band and PLC band) is a phenomenon frequently observed in cold-rolled medium Mn steels. In this study, through a number of quasi-static uniaxial tensile tests with digital image correlation (DIC) measurement of the strain rate field, we found the medium Mn steel (Fe-0.14C-7.14Mn-0.23Si wt. pct with approximately 33 vol pct of retained austenite and 67 vol pct of ferrite) exhibited distinct competition/coordination between the Luders band and the PLC band at different deformation temperatures: (1) at 25 °C and 55 °C, a Luders band was followed by several PLC bands; (2) at 100 °C, fracture occurred right after the Luders band formation, without the presence of a PLC band; (3) at 250 °C, only PLC bands were observed. We propose that these macroscopic behaviors can be explained by the temperature-dependent conditions for the formation/appearance and propagation of Luders bands and PLC bands. The propagation of Luders bands becomes difficult when the temperature increases as less hardening is provided by martensitic transformation. In contrast, the appearance and propagation of PLC bands become easier when the temperature increases and/or the plastic strain becomes large (16.5 and 18.9 pct in this material at the deformation temperatures of 25 °C and 55 °C, respectively), as the difference in the average velocities of solute atom diffusion and dislocation gliding is reduced. Either condition for Luders bands or for PLC bands will be satisfied at different deformation temperatures or plastic strains, thus leading to the competition/coordination between them.

Characterization of non-linear mechanical behavior of the cornea

The objective of this study was to evaluate which hyperelastic model could best describe the non-linear mechanical behavior of the cornea, in order to characterize the capability of the non-linear model parameters to discriminate structural changes in a damaged cornea. Porcine corneas were used, establishing two different groups: control (non-treated) and NaOH-treated (damaged) corneas (n = 8). NaOH causes a chemical burn to the corneal tissue, simulating a disease associated to structural damage of the stromal layer. Quasi-static uniaxial tensile tests were performed in nasal-temporal direction immediately after preparing corneal strips from the two groups. Three non-linear hyperelastic models (i.e. Hamilton-Zabolotskaya model, Ogden model and Mooney-Rivlin model) were fitted to the stress–strain curves obtained in the tensile tests and statistically compared. The corneas from the two groups showed a non-linear mechanical behavior that was best described by the Hamilton-Zabolotskaya model, obtaining the highest coefficient of determination (R2 > 0.95). Moreover, Hamilton-Zabolotskaya model showed the highest discriminative capability of the non-linear model parameter (Parameter A) for the tissue structural changes between the two sample groups (p = 0.0005). The present work determines the best hyperelastic model with the highest discriminative capability in description of the non-linear mechanical behavior of the cornea.

Experimental and numerical analysis of the heat generated by plastic deformation in quasi-static uniaxial tensile tests

This study evaluates the temperature variation observed in quasi-static uniaxial tensile tests, due to the heat generated by plastic deformation. The AA6016-T4 aluminium alloy was the material selected, considering different values of crosshead velocity (from 0.01 mm/s up to 1 mm/s). The temperature variation was also evaluated during the stress relaxation test. A finite element model of the uniaxial tensile test is presented, which takes into account the heat generated by plastic deformation, as well as the effect of the heat losses to the environment (convective heat transfer coefficient) and to the grips (interfacial heat transfer coefficient). The numerical results show that the predicted temperature variation is almost independent of the selected heat transfer coefficients. On the other hand, the temperature rise is influenced by the Taylor–Quinney coefficient. The comparison between experimental and numerical temperatures shows that the Zehnder model (increasing Taylor–Quinney coefficient) provides more accurate results than the Aravas model (decreasing Taylor–Quinney coefficient). Nevertheless, the evolution of the Taylor–Quinney coefficient defined by the Zehnder model assumes a constant value for the hardening coefficient, which does not fit the hardening behaviour observed for this aluminium alloy.

Investigation of the electromechanical behaviors in Cu-stabilized GdBCO coated conductor tapes using high-cycle fatigue tests at 77 K and related fractographic observations

In applications employing high-temperature superconducting conductors, various cyclic loading (fatigue) conditions produced by mechanical, thermal, or periodic electromagnetic forces are inevitable. Applying coated conductor (CC) tapes under fatigue loading conditions is expected to critically affect the long-term reliability of its superconducting performance. Most studies evaluating the mechanical and electromechanical characteristics use quasi-static uniaxial tensile tests. Few have focused on the characterization of CC tapes under fatigue loading. In this study, the electromechanical property characterization of Cu-stabilized GdBa2Cu3Oy (GdBCO) CC tapes including fatigue behaviors were investigated at 77 K. High-cycle uniaxial fatigue tests were carried out on GdBCO CC tapes 4 and 12 mm in width, and the two were compared in terms of mechanical and electromechanical aspects at a stress ratio of 0.1. The mechanical and electrical fatigue limits of the CC tapes were determined at 77 K. The 4 mm wide CC tapes showed less fatigue limits when compared to the 12 mm wide ones. However, regardless of the CC tape width, the sequence in the obtained characteristic strengths at 77 K was the same: yield strength > irreversible stress limit > mechanical fatigue limit > electrical fatigue limit. Fracture surface morphologies were observed using scanning electron microscopy-energy dispersive x-ray spectroscopy and electron probe micro-analysis to clarify the fatigue fracture mechanism and to examine the influence of the architecture of the CC tapes on fatigue behaviors. Damage along the edges, caused by slitting during fabrication of the 4 mm wide CC tapes, generated a stress concentration, eventually resulting in earlier crack initiation not only on the substrate, reducing mechanical fatigue strength, but also on the superconducting layer, degrading the measured critical current.

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.

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.

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.

Effect of Filler Functionalization on the Thermo-Mechanical behavior of Polypropylene Nanocomposites

Present study is an experimental attempt to characterize the thermo-mechanical behavior of Thermoplastic polymer nanocomposites (PNC) surface functionalized with multi walled carbon nanotubes (MWCNT). Nanocomposites with two grades of MWCNT, pristine and –COOH functionalized were fabricated with isotactic polypropylene (iPP) and results were compared. Nanocomposites Films with 0%, 0.5%, 1% and 2% MWCNT loadings were prepared by conventional solution casting method followed by isothermal quasi static uniaxial tensile tests at constant strain rates of 0.1/min, cyclic tensile tests at strain rate of 0.1/min and isochronous creep characterization at stress levels of 0.2, 0.5, 1, 2, 5, 7, 10, 12 and 15 MPa performed on Tinius-Olsen Universal Testing machine to monitor strength and stiffness of the material and obtain the threshold of stress and time at room temperature to observe the transition from linear to nonlinear viscoelastic regime. Dynamic characterization at constant frequency of 1 Hz, temperature ramp 0-100°C, was performed to obtain storage modulus under dynamic loading conditions on Dynamic mechanical analyzer (DMA). It was reported that incorporation of functionalized MWCNT increases the strength, failure strain, reduces creep strain and increases stiffness of nanocomposites as compared to those with pristine-MWCNT up to 1% concentration. Moreover, it was also observed that loading under 1MPa and 5 seconds, the material behaves linearly. Prior to the testing, thermal stability of materials was monitored by Thermo-gravimetric analysis.

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.

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.

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.

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.

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.