Showing papers on "Strain rate published in 2016"
TL;DR: In this paper, an electrically conductive ultralow percolation threshold of 0.1 wt% graphene was observed in the thermoplastic polyurethane (TPU) nanocomposites.
Abstract: An electrically conductive ultralow percolation threshold of 0.1 wt% graphene was observed in the thermoplastic polyurethane (TPU) nanocomposites. The homogeneously dispersed graphene effectively enhanced the mechanical properties of TPU significantly at a low graphene loading of 0.2 wt%. These nanocomposites were subjected to cyclic loading to investigate the influences of graphene loading, strain amplitude and strain rate on the strain sensing performances. The two dimensional graphene and the flexible TPU matrix were found to endow these nanocomposites with a wide range of strain sensitivity (gauge factor ranging from 0.78 for TPU with 0.6 wt% graphene at the strain rate of 0.1 min−1 to 17.7 for TPU with 0.2 wt% graphene at the strain rate of 0.3 min−1) and good sensing stability for different strain patterns. In addition, these nanocomposites demonstrated good recoverability and reproducibility after stabilization by cyclic loading. An analytical model based on tunneling theory was used to simulate the resistance response to strain under different strain rates. The change in the number of conductive pathways and tunneling distance under strain was responsible for the observed resistance-strain behaviors. This study provides guidelines for the fabrication of graphene based polymer strain sensors.
474 citations
TL;DR: In this article, the authors compare different methods of measuring the yield stress with conventional rheometers that have been used in the literature on a variety of materials and conclude that the differences between the various methods are significant.
Abstract: Yield stress materials are ubiquitous, yet the best way to obtain the value of the yield stress for any given material has been the subject of considerable debate. Here we compare different methods of measuring the yield stress with conventional rheometers that have been used in the literature on a variety of materials. The main conclusion is that, at least for well-behaved (non-thixotropic) materials, the differences between the various methods are significant; on the other hand, the scaling of the measured yield stress with the volume fraction of dispersed phase shows the same dependence independently of the way in which the yield stress is obtained experimentally. The measured yield strain is similarly found to depend on the method employed. The yield stress values obtained for a simple (non-thixotropic) yield stress fluid are only similar for Herschel–Bulkley fits and stress-strain curves obtained from oscillatory measurements. Stress-strain curves with a continuous imposed stress or strain rate differ significantly, as do oscillatory measurements of the crossover between G′ and G″ or the point where G′ starts to differ significantly from its linear response value. The intersection of the G′ and G″ curves as a function of strain consistently give the highest value of the yield stress and yield strain. In addition, many of these criteria necessitate some arbitrary definition of a crossover point. Similar conclusions apply for a class of thixotropic yield stress materials, with the stress-strain curve from the oscillatory data giving the dynamic yield stress and the Herschel–Bulkley fit either the static or dynamic yield stress, depending on how the measurement is carried out.
226 citations
TL;DR: In this article, a review of the methods for dynamic loading of polymers is presented, where the high strain rate mechanical properties of several polymers, i.e. glassy and rubbery amorphous polymers and semi-crystalline polymers are reviewed.
Abstract: The mechanical properties of polymers are becoming increasingly important as they are used in structural applications, both on their own and as matrix materials for composites. It has long been known that these mechanical properties are dependent on strain rate, temperature, and pressure. In this paper, the methods for dynamic loading of polymers will be briefly reviewed. The high strain rate mechanical properties of several classes of polymers, i.e. glassy and rubbery amorphous polymers and semi-crystalline polymers will be reviewed. Additionally, time–temperature superposition for rate dependent large strain properties and pressure dependence in polymers will be discussed. Constitutive modeling and shock properties of polymers will not be discussed in this review.
209 citations
TL;DR: In this paper, the evolution of dynamic recrystallization (DRX) grains and δ phase, as well as the interactions between DRX grains and the phase were investigated.
206 citations
TL;DR: In this article, a multi-level constitutive model for polycrystalline metals that deform by a combination of elasticity, slip and deformation twinning was developed, where the first level uses an upper bound Taylor-type crystal plasticity (T-CP) theory to relate the single-crystal scale to the polycrystal meso-scale and the second level employs an implicit finite elements (FE) approach to relate meso scale to macro-scale.
169 citations
15 Dec 2016-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effects of strain, strain rate and deformation temperature on the subgrain structures, local and cumulative misorientations and twinning phenomena of an IN718 superalloy were investigated.
Abstract: The hot deformation behavior of an IN718 superalloy was studied by isothermal compression tests under the deformation temperature range of 950–1100 °C and strain rate range of 0.001–1 s−1 up to true strains of 0.05, 0.2, 0.4 and 0.7. Electron backscattered diffraction (EBSD) technique was employed to investigate systematically the effects of strain, strain rate and deformation temperature on the subgrain structures, local and cumulative misorientations and twinning phenomena. The results showed that the occurrence of dynamic recrystallization (DRX) is promoted by increasing strain and deformation temperature and decreasing strain rate. The microstructural changes showed that discontinuous dynamic recrystallization (DDRX), characterized by grain boundary bulging, is the dominant nucleation mechanism in the early stages of deformation in which DRX nucleation occurs by twining behind the bulged areas. Twin boundaries of nuclei lost their ∑3 character with further deformation. However, many simple and multiple twins can be also regenerated during the growth of grains. The results showed that continuous dynamic recrystallization (CDRX) is promoted at higher strains and large strain rates, and lower temperatures, indicating that under certain conditions both DDRX and CDRX can occur simultaneously during the hot deformation of IN718.
162 citations
TL;DR: The nature of the monomer system determines the amount of the bulk contraction that occurs during polymerization and the resultant stress, and higher values of shrinkage strain and stress were demonstrated by the investigated flowable materials.
130 citations
TL;DR: In this paper, a metastable β Ti-10V-3Fe-3Al 0.27O (wt.%) alloy was subjected to thermo-mechanical processing to induce α and ω phase formation, so that the alloy can exhibit the features responsible for both transformation induced plasticity (TRIP) and TWIP) behaviour during deformation.
126 citations
TL;DR: In this article, the role of strain rate on the microstructural evolution during hot deformation of a hot isostatically processed nickel base superalloy was analyzed using EBSD analysis.
126 citations
TL;DR: In this article, the authors investigated the dynamic damage and fracture behavior of concrete under compression with strain rate up to 100 ǫ s−1 by Monte Carlo simulations (MCSs) of realistic meso-scale models based on high-resolution micro-scale X-ray computed tomography (XCT) images.
125 citations
TL;DR: In this article, the influence of strain rate on the tensile properties of composite materials was investigated in the range of strain rates from 0.0016 s − 1 to 542 s −1.
Abstract: Composites are efficient to deal with tensile loads than metals. Now-a-days, metals are replaced with composites owing to their higher strength to weight ratio and are extensively used in aircraft wing and fuselage structures. These structures are subjected to high strain rates during impact loadings, such as bird hit or run-way debris impact. In order to design robust composite structures, it is important to understand the strain-rate-dependent behavior of composite materials. In this study, influence of strain rate on the tensile properties of glass/epoxy, carbon/epoxy and hybrid (glass-carbon/epoxy) composites are experimentally and theoretically investigated in the range of strain rates from 0.0016 s −1 to 542 s −1 . Drop mass setup is used for high strain rate tests. Quasi-static tests are performed on Instron universal testing machine in accordance with ASTM D638 . The results indicate that the tensile strength and tensile modulus of GFRP and hybrid composites increase and percentage of failure strain for GFRP, CFRP and Hybrid composites decreases with the increase in strain rate, whereas tensile strength and tensile modulus of CFRP composites remains approximately constant. The scanning electron microscopy is used for analyzing the failure modes of the failed region (surface) of the tested specimens. Non contact DIC system is used to capture the strain field with the help of high speed camera.
TL;DR: In this article, the authors present a systematic study on the mechanical properties and behavior of Kuru Gray granite at confining pressures up to 225 MPa and at strain rates of 10 −6 ǫ s −1 and 600 s − 1.
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TL;DR: The study of flow of non-Newtonian fluids in porous media is very important and serves a wide variety of practical applications in processes such as enhanced oil recovery from underground reservoirs, filtration of polymer solutions and soil remediation through the removal of liquid pollutants as mentioned in this paper.
Abstract: The study of flow of non-Newtonian fluids in porous media is very important and serves a wide variety of practical applications in processes such as enhanced oil recovery from underground reservoirs, filtration of polymer solutions and soil remediation through the removal of liquid pollutants. These fluids occur in diverse natural and synthetic forms and can be regarded as the rule rather than the exception. They show very complex strain and time dependent behavior and may have initial yield-stress. Their common feature is that they do not obey the simple Newtonian relation of proportionality between stress and rate of deformation. Non-Newtonian fluids are generally classified into three main categories: time-independent whose strain rate solely depends on the instantaneous stress, time-dependent whose strain rate is a function of both magnitude and duration of the applied stress and viscoelastic which shows partial elastic recovery on removal of the deforming stress and usually demonstrates both time and strain dependency. In this article, the key aspects of these fluids are reviewed with particular emphasis on single-phase flow through porous media. The four main approaches for describing the flow in porous media are examined and assessed. These are: continuum models, bundle of tubes models, numerical methods and pore-scale network modeling.
TL;DR: In this paper, the authors investigated the variation of the mechanical properties and cracking behaviors under both the dynamic and quasi-static strain rate conditions, and found that the compressive strength, the nominal elastic modulus and the failure strain of the gypsum specimens increase apparently with the strain rate.
10 Jan 2016-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a comprehensive and scientific constitutive models based on the Arrhenius type equation have been developed from the experimentally measured data, where the deformation temperature and strain rate have significant effect on flow stress and the material constants, such as α, β, n, ln A and Q are the functions of the strain.
Abstract: Isothermal compression tests of a new type Al–Zn–Mg–Er–Zr alloy are carried out on a Gleeble-3800 thermal simulator at temperatures varying from 300 to 460 °C and strain rates ranging from 0.001 to 10 s −1 . A comprehensive and scientific constitutive models based on the Arrhenius type equation have been developed from the experimentally measured data. The deformation temperature and strain rate have significant effect on flow stress and the material constants, such as α, β, n, ln A and Q are the functions of the strain. The flow stress calculated by the developed constitutive equation shows a close agreement with the experimental value, which indicates that the proposed constitutive equation can precisely analyze the hot deformation behavior of the Al–Zn–Mg–Er–Zr alloy. Due to the presence of coherent L1 2 -structured Al 3 (Er,Zr) precipitates, the dominant softening mechanism is dynamic recovery during isothermal compression.
10 Jan 2016-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of deformation temperature and strain rate on the stress-strain behavior, microstructure evolution and dynamic recrystallization (DRX) during hot deformation was investigated using the isothermal compression tests in the strain rate of 0.001−0.1−s−1 at the temperature range of 800-1200°C.
Abstract: The hot deformation characteristics of dynamic recrystallization (DRX) of the MoNbHfZrTi refractory high-entropy alloy (HEA) was investigated using the isothermal compression tests in the strain rate of 0.001–0.1 s−1 at the temperature range of 800–1200 °C. Scanning electron microscope (SEM) with the electron backscatter diffraction (EBSD) technique was used to study the effect of deformation temperature and strain rate on the stress–strain behavior, microstructure evolution and dynamic recrystallization (DRX) during hot deformation. At 800 °C, the stress–strain curve exhibits a work-hardening stage until fracture at the strain rate of 0.1 s−1 and 0.01 s−1. Under other deformation conditions, the stress–strain curves exhibit the typical DRX characteristics. On the whole, the stress decreases with the increase of deformation temperature and decrease of the strain rate. The initial dendritic structure gradually disappears and more dynamic recrystallized grains form with the decrease of strain rate and the increase of the deformation temperature. The nucleation mechanism of discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) occurred simultaneously for the MoNbHfZrTi alloy during hot deformation. The effect of CDRX was weakened with the increase of deformation temperature and with the decrease of strain rate.
TL;DR: In this article, the behavior of high-strength and normal-strength strain-hardening cement-based composites (SHCCs) made of fine-grained matrix and high-density polyethylene fibers under quasi-static and impact tensile loading was described.
26 Apr 2016-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the flow behavior, microstructure evolution and softening mechanism of an AA7085 aluminum alloy are investigated by isothermal hot compression tests at 450°C with the strain rates of 0.001 s−1 and 0.1 s− 1.
Abstract: The flow behavior, microstructure evolution and softening mechanism of an AA7085 aluminum alloy are investigated by isothermal hot compression tests at 450 °C with the strain rates of 0.001 s−1 and 0.1 s−1. Optical microscopy (OM), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) are used to characterize microstructure evolution during deformation. The results reveal that the flow stress curves exhibit a single peak and then two types of flow stress curves are found in the present study. Microstructure characterization reveals that dynamic recovery (DRV) and recrystallization (DRX) occur in the both conditions. The microstructure discrepancy becomes significant with increasing strain rate after a certain strain level (e≥0.3). In the case of 0.001 s−1, the dynamic recovery is thought to precede continuous dynamic recrystallization. As the strain rate increased, the absence of dynamic recovery provides enough stored energy for discontinuous dynamic recrystallization (DDRX), resulting in a retardation in the occurrence of continuous dynamic recrystallization (CDRX).
TL;DR: In this paper, the elastoplastic self-consistent (EPSC) polycrystal plasticity code, including the recently developed twinning-detwinning (TDT) model, is used to describe the homogeneous plastic flow of rare earth containing Mg alloy, WE43-T5, plate at quasistatic and dynamic strain rates.
TL;DR: In this paper, the properties and behaviour of an α−β colony Ti-6242 alloy have been investigated at 20°C utilising coupled micro-pillar stress relaxation tests and computational crystal plasticity.
Abstract: The properties and behaviour of an α−β colony Ti-6242 alloy have been investigated at 20 °C utilising coupled micro-pillar stress relaxation tests and computational crystal plasticity. The β-phase slip strength and intrinsic slip system strain rate sensitivity have been determined, and the β-phase shown to have stronger rate sensitivity than that for the α phase. Close agreement of experimental observations and crystal plasticity predictions of micro-pillar elastic-plastic response, stress relaxation, slip activation in both α and β-phases, and strain localisation within the α−β pillars with differing test strain rate, β morphology, and crystal orientations is achieved, supporting the validity of the properties extracted. The β-lath thickness is found to affect slip transfer across the α−β−α colony, but not to significantly change the nature of the slip localisation when compared to pure α-phase pillars with the same crystallographic orientation. These results are considered in relation to rate-dependent deformation, such as dwell fatigue, in complex multiphase titanium alloys.
TL;DR: In this article, the effect of strain rate on the uniaxial cyclic deformation of a super-elastic NiTi shape memory alloy (SMA) was investigated.
TL;DR: In this article, the strain rate behavior in tension of the S355 structural steel using a modified Split Hopkinson Tensile Bar for the mechanical characterisation at high strain rates (300, s - 1, 500, s − 1 and 850 ǫ s -1 ), and a Hydro Pneumatic Machine for intermediate strain rates, were collected with the intention of setting down the basis for the enhancement of a progressive collapse analysis, that is, by the way, a dynamic event.
TL;DR: In this article, the determining role of grain size and strain rate on the mechanical behavior of a series of twinning induced plasticity steels (Fe-20Mn-0.6C) with average grain size in the range of 3.5-25μm was elucidated.
TL;DR: In this article, an assessment of the empirical reactive force field ReaxFF to predict the formation of amorphous silica from its crystalline structure and the determination of mechanical properties under tension using molecular dynamics simulations is presented.
Abstract: Assessment of the empirical reactive force field ReaxFF to predict the formation of amorphous silica from its crystalline structure and the determination of mechanical properties under tension using molecular dynamics simulations is presented. Detailed procedures for preparing amorphous silica from crystalline silica are presented and the atomic structure is in good agreement with experimental results. Tensile properties of silica are predicted over a wide range of strain rates (2.3 × 108 s−1–1.0 × 1015 s−1) allowing comparison with results reported in the literature for other force fields. Quasi-static modulus obtained from power-law fitting of the low-stain rate modulus predicted by ReaxFF is in good agreement with experimental results. A transition strain rate of approximately $$ 2.5 \times 10^{11} {\text{s}}^{ - 1} $$
is identified where modulus increases rapidly to a plateau level. Tensile strength also increases significantly in this range of strain rate and plateaus at the theoretical upper bound for silica. A detailed study is presented to understand the mechanisms associated with strain rate effects on the overall stress–strain response of silica. Bond breakage which evolves into void growth leading to failure is predicted to occur at approximately 27 % strain for all strain rates. Stress relaxation simulations indicates that the transition strain rate occurs when the characteristic time for high-strain rate loading and stress relaxation times are the same order. The effects of cooling rate and temperature on the structure and the stress–strain response of the silica glass are also investigated. Low-cooling rate and low-cooling temperature enhance the properties of silica.
TL;DR: In this paper, a disintegrated melt deposition method was used to synthesize graphene nanoplatelets reinforced AZ61 magnesium alloy, which was subjected to homogenization at 430°C for 24h and extruded at 350°C with the ratio of 5.2:1.
TL;DR: In this article, a simple viscoelastic model based on the Kelvin-Voigt model was proposed for the two types of separators to investigate material anisotropy and strain rate effects, tensile tests conducted on MTS and Instron at various strain rates from 0.01 to 50 s−1 were carried out with samples prepared at three different directions: transverse direction (TD, 0°), machine direction (MD, 90°) and 45°.
TL;DR: The first experimental demonstration of macrodeformation twins in single-crystal aluminum formed under an ultrahigh strain rate (∼10^{6} s^{-1}) and large shear strain via dynamic equal channel angular pressing is presented.
Abstract: Deformation twinning in pure aluminum has been considered to be a unique property of nanostructured aluminum. A lingering mystery is whether deformation twinning occurs in coarse-grained or single-crystal aluminum at scales beyond nanotwins. Here, we present the first experimental demonstration of macrodeformation twins in single-crystal aluminum formed under an ultrahigh strain rate (∼10^{6} s^{-1}) and large shear strain (200%) via dynamic equal channel angular pressing. Large-scale molecular dynamics simulations suggest that the frustration of subsonic dislocation motion leads to transonic deformation twinning. Deformation twinning is rooted in the rate dependences of dislocation motion and twinning, which are coupled, complementary processes during severe plastic deformation under ultrahigh strain rates.
TL;DR: In this paper, in-situ micropillar compression was performed to investigate the local strain rate sensitivity of single α phase in dual-phase Ti alloy, Ti-6Al-2Sn-4Zr-2Mo (wt%).
TL;DR: In this paper, the room temperature intrinsic strain rate sensitivities (SRS) of basal and prismatic slip systems have been determined for the α (HCP) phase of a titanium alloy (Ti-6242), through coupled crystal plasticity modelling and micro-pillar compression experiments.
TL;DR: In this paper, the dynamic mechanical behavior of the magnetically responsive shear-stiffening gel (MSTG) was investigated by using a modified Split Hopkinson Pressure Bar (SHPB) system.