Strain Rate Tensile Research Articles

Regional White Matter Diffusion Changes Associated with the Cumulative Tensile Strain and Strain Rate in Nonconcussed Youth Football Players.

The purpose of this study is to assess the relationship between regional white matter diffusion imaging changes and finite element strain measures in nonconcussed youth football players. Pre- and post-season diffusion-weighted imaging was performed in 102 youth football subject-seasons, in which no concussions were diagnosed. The diffusion data were normalized to the IXI template. Percent change in fractional anisotropy (%ΔFA) images were generated. Using data from the head impact telemetry system, the cumulative maximum principal strain one times strain rate (CMPS1 × SR), a measure of the cumulative tensile brain strain and strain rate for one season, was calculated for each subject. Two linear regression analyses were performed to identify significant positive or inverse relationships between CMPS1 × SR and %ΔFA within the international consortium for brain mapping white matter mask. Age, body mass index, days between pre- and post-season imaging, previous brain injury, attention disorder diagnosis, and imaging protocol were included as covariates. False discovery rate correction was used with corrected alphas of 0.025 and voxel thresholds of zero. Controlling for all covariates, a significant, positive linear relationship between %ΔFA and CMPS1 × SR was identified in the bilateral cingulum, fornix, internal capsule, external capsule, corpus callosum, corona radiata, corticospinal tract, cerebral and middle cerebellar peduncle, superior longitudinal fasciculus, and right superior fronto-occipital fasciculus. Post hoc analyses further demonstrated significant %ΔFA differences between high-strain football subjects and noncollision control athletes, no significant %ΔFA differences between low-strain subjects and noncollision control athletes, and that CMPS1 × SR significantly explained more %ΔFA variance than number of head impacts alone.

Effect of Tensile–Strain Rate and Specimen Width on Mechanical Properties of Cold-Formed Q345 Steel at Elevated Temperatures

AbstractThe objective of this paper is to to ascertain the reliable mechanical properties of cold-formed Q345 steel at elevated temperatures while considerting the effects of tensile strain rate an...

Compression and spallation properties of polyethylene terephthalate under plate impact loading

We conduct plate impact experiments to investigate shock compression and spallation properties of polyethylene terephthalate. The Hugoniot equation of state, the apparent velocity–particle velocity relation, and the indices of refraction are obtained from Hugoniot experiments. Spall strength, as well as tensile strain rate is deduced at shock pressures up to ∼2.4 GPa in spallation shots. At low shock pressures (<0.6 GPa), the spall strength increases slightly with increasing shock pressure, as a result of increasing tensile strain rate. Release melting is observed at high impact velocities (>816 m s−1). Via X-ray computed tomography, three-dimensional void and crack structures are revealed for shock-recovered specimens. Small voids appear thin and curved for low-speed impacts but become ellipsoidal for high-speed impacts. Such different void shapes may be attributed to the diverse damage mechanisms at different impact velocities.

The simulation of 3D hypervelocity spallation using a hydrocode PAGOSA with FLIP+MPM

In this work, a hydrocode PAGOSA with FLIP+MPM is presented and exercised to investigate the fracture in ductile material. The merit of PAGOSA with FLIP+MPM to solve the advection problem is first illustrated by a solid piston periodically moving in a sealed tube with air. Furthermore, the ability of PAGOSA with FLIP+MPM to capture the fracture in material is shown by a simple stretching fracture in ductile material. In both of two benchmark problems, the PAGOSA results and analytical solutions are also presented for comparison. Then PAGOSA with FLIP+MPM is used to model complex spall in ductile material, which is a challenging problem in engineering applications. The convergences of PAGOSA with FLIP+MPM—based on both the mesh size and the marker density—are investigated by monitoring free surface velocity. To further show the ability of PAGOSA with FLIP+MPM to predict fracture in ductile material, the numerical results are compared with the experimental results and other published numerical results. Moreover, the effect of the spall parameter in PAGOSA with FLIP+MPM on the numerical simulation is also analyzed by investigating the free surface velocity. Finally, the effects of the peak compressive stress, the tensile strain rate, and the loading rate on the spallation are further investigated. The numerical results show that PAGOSA with FLIP+MPM can improve PAGOSA's performance when applied to predicting fracture in ductile materials, and is robust enough to accurately predict spall fracture in ductile materials.

General Analytical Solutions for Dynamic Load-Carrying Capacity of Brittle Materials Under an Arbitrary Incident Stress Wave

In this study, two general solutions for the dynamic tensile load-carrying capacity of brittle materials subject to an arbitrary incident stress wave in the form of Fourier integrals are derived. In order to verify the general solutions, we reduce them to three particular solutions, respectively, i.e., trapezoidal pulse, quadratic pulse and cubic pulse. It is found that all of them can well capture the experimental trends in the previous studies. In between, the first two particular solutions can exactly accord with the two previous analytical solutions under the same boundary conditions, respectively. Therefore, for arbitrary tensile boundary pulses, the dynamic tensile strength of the brittle materials can be calculated from static parameters and characteristics of external loading. This study improves the credibility of the previous works that working on deriving the dynamic load-carrying capacity through analytical methods, and thus, consolidate their theoretical foundation. Meanwhile, on basis of the general solution, the relation between the dynamic tensile load-carrying capacity and strain rate can be further deduced by combining static parameters, hence, it could be inappropriate to claim the strain rate effect on tensile strength as an intrinsic material property anymore. In addition, we found that the process to obtain an explicit analytical solution becomes increasingly difficult with the increased complexity of waveform for an incident pulse, or even no explicit solution can be obtained.

Preparation and Properties of Modified Graphene Reinforced Aluminum Matrix Composites

In order to solve the problem of agglomeration of graphene in preparation of composites, GN-CeO2 powders with even dispersion were obtained by a hydrothermal reduction method, which involved modifying the surface of acidified graphene by cerium nitrate. Then, Al/GN-CeO2 composite powders and materials were prepared by high-energy ball milling and vacuum hot pressing, respectively. The details were investigated, including the effect of modification process on the surface morphology and functional groups of graphene and modification time on the properties of Al/GN-CeO2 composites. The result shows that the functional groups and defects of graphene were added by the treatment of acidification process, which is beneficial to the composite of graphene and CeO2 particles. The quantity of CeO2 deposition on graphene surface increased with the duration of hydrothermal reduction time. After 6 h modification, the properties of the composites performed best. Compared with Al/GN composites, the tensile strength of the modified composites was increased from 284 MPa to 321 MPa; and the tensile strain rate of the modified composites was increased to 12.3%；the hardness of the modified composites was increased from 97.1 Hv to 99.5 Hv；the conductivity of the modified composites was increased from 29.84%IACS to 33.21%IACS.

Cyclic Behavior of Reinforced High Strain-Hardening UHPC under Axial Tension.

The cyclic tensile behavior of steel-reinforced high strain-hardening ultrahigh-performance concrete (HSHUHPC) was investigated in this paper. In the experimental program, 12 HSHUHPC specimens concentrically placed in a single steel reinforcement under cyclic uniaxial tension were tested, accompanied by acoustic emission (AE) source locating technology, and 4 identical specimens under monotonic uniaxial tension were tested as references. The experimental variables mainly include the loading pattern, the diameter of the embedded steel rebar, and the level of target strain at each cycle. The tensile responses of the steel-reinforced HSHUHPC specimens were evaluated using multiple performance measures, including the failure pattern, load–strain response, residual strain, stiffness degradation, and the tension-stiffening behavior. The test results showed that the enhanced bond strength due to the inclusion of steel fibers transformed the failure pattern of the steel-reinforced HSHUHPC into a single, localized macro-crack in conjunction with a sprinkling of narrow and closely spaced micro-cracks, which intensified the strain concentration in the embedded steel rebar. Besides, it was observed that the larger the diameter of the embedded steel rebar, the smaller the maximum accumulative tensile strain under cyclic tension, which indicated that the larger the diameter of the embedded steel rebar, the greater the contribution to the tensile stiffness of steel-reinforced HSHUHPC specimens in the elastic–plastic stage. In addition, it was found that a larger embedded steel rebar appeared to reduce the tension-stiffening effect (peak tensile strength) of the HSHUHPC. Moreover, the residual strain and the stiffness of the steel-reinforced HSHUHPC were reduced by increasing the number of cycles and finally tended toward stability. Nevertheless, different target strain rates in each cycle resulted in different eventual cumulative tensile strain rates; hence the rules about failure pattern, residual strain, and loading stiffness were divergent. Finally, the relationship between the accumulative tensile strain and the loading stiffness degradation ratio under cyclic tension was proposed and the tension-stiffening effect was analyzed.

Tensile fracture behavior and texture evolution of a hot-rolled W–Y2(Zr)O3 alloy

• A W–0.4wt% Y 2 (Zr)O 3 alloy with high recrystallization temperature and superior tensile strength have been prepared. • The strength and elongation of the RD and TD orientation samples of the WYZ alloy depend on the length of the free dislocation slip path and the capacity of grains to dislocations. • With the increase of tensile temperature, the α- and γ-fiber texture on the fracture side surface were significantly enhanced. • Larger tensile strain rates overestimate DBTT but exhibit high tensile strength at temperatures above DBTT. A W–0.4wt% Y 2 (Zr)O 3 (WYZ) alloy plate with superior mechanical properties and improved high-temperature stability was prepared by hot rolling. The tensile properties of WYZ alloys with different orientations and recrystallization states were investigated at a temperature range from room temperature (RT) to 500°C. The texture intensity of the original WYZ alloy was weak, but it was significantly enhanced after annealing. The initial recrystallization temperature of the WYZ alloy was approximately 1400°C. After recrystallization annealing, the strength of the WYZ alloy decreased significantly, but it showed an increased ductility. The ultimate tensile strength and fracture elongation of the samples along the rolling direction (RD) were always significantly higher than those of the samples along the transverse direction (TD). Orientation and annealing had no evident effect on ductile-to-brittle transition temperature (DBTT) from tensile data, but increasing strain rate would overestimate DBTT. The DBTT of the WYZ alloy from tensile data was approximately between 200°C and 300°C. With the increase in tensile test temperature, the strengths of α- and γ-fiber textures on the side of fracture surface increased significantly. The increase in α- and γ-fiber texture contents was beneficial to ductility enhancement in the WYZ plate.

Quasi-static and low-velocity impact biaxial flexural fracture of aluminosilicate glass — An experimental and numerical study

In this study, the quasi-static biaxial fracture behavior of aluminosilicate glass is investigated via Ball-On-Ring (BOR) and Ring-On-Ring (ROR) tests aided by a three-dimensional Digital Image Correlation (3D-DIC) technique. In-plane strain field and out of plane deformation distribution during the loading process can be obtained by this test system, overcoming the problem of inaccurate displacement data provided by the loading machine. During the loading process, a uniform strain distribution field is formed below the load ring of the ROR specimen while a gradient strain distribution is built for the BOR specimens. For dynamic loading conditions, low-velocity impact BOR tests are conducted at velocities of 2 m/s and 4 m/s showing a dynamic strengthening effect and high-speed cameras provide detailed fracture and failure sequences of the glass plates. Finite Element Method (FEM) simulations with the JH-2 material model are carried out showing good consistency with experimental results for the quasi-static loading conditions. FEM coupled to Smooth Particle Hydrodynamics (FEM-SPH) technique is utilized for dynamic simulations to solve the element distortion and non-physical problems. The influence of the tensile strain rate effect on low-velocity impact behavior of aluminosilicate glass is analyzed in detail. The original JH-2 model does not provide a reasonable prediction of the dynamic tensile response of brittle materials and the model requires further modifications to describe the dynamic tensile fracture behavior. By introducing rate-dependence maximum hydrostatic tensile strength σt,max to the updated model, better predictions for the contact force and projectile residual velocity histories of low-velocity impact tests can be provided.

Dynamic tensile behavior of steel strands at different strain rates

In engineering structures, steel strands can be subjected to dynamic loads associated with earthquakes, vehicle impacts, explosions and other special circumstances occurring in addition to static loads and resulting in higher strain rates. Therefore, it is of great significance to study the mechanical performance of steel strands subjected to dynamic loads at high strain rates. In this study, first an electrohydraulic high-speed impact test system, an electrohydraulic servo shear-stress test system, and a universal testing machine were used to conduct the dynamic tensile tests on single-wire, single-bundle, and four-bundle steel strands at ten different strain rates (2.73 × 10−3–10.714 s−1), and the influences of the strain rate and strand diameter on the mechanical behavior of steel strands were analyzed based on the experimental data. At the same time, the wire breakage, failure modes, and fracture forms were analyzed, and the Ramberg-Osgood and Johnson-Cook constitutive models were revised to obtain a constitutive relationship which, along with the related material parameters, better describes the stress–strain behavior of the tensile steel strands subjected to dynamic tensile loads. The results show that the steel strands are clearly sensitive to strain rate, which is higher in quasi-static states and at low strain rates. At higher strain rates, the sensitivity to strain rate decreases, and the sensitivity of yield strength is higher than the ultimate strength. The strand diameter has certain influence on the steel strands performance. The ultimate strains of the single-wire and four-bundle steel strands are all smaller than that of the single-bundle steel strands. Twisting of the single-bundle steel strands weakened the wires and resulted in premature wire breakage. The failure modes of steel strands subjected to different tensile strain rates shifted from ductile to brittle. The failure modes were mainly of three types, namely, necking-milling, splitting-milling, and splitting. The Ramberg-Osgood and the Johnson-Cook constitutive models with the Cowper-Symonds strain rate parameter correction can more accurately reflect the variation in the strain hardening characteristics of steel strands with strain rate.

Crystal rotations and alignment in spatially varying magma flows: 2-D examples of common subvolcanic flow geometries

Summary Elongate inclusions immersed in a viscous fluid generally rotate at a rate that is different from the local angular velocity of the flow. Often, a net alignment of the inclusions develops, and the resulting shape preferred orientation of the particle ensemble can then be used as a strain marker that allows reconstruction of the fluid’s velocity field. Much of the previous work on the dynamics of flow-induced particle rotations has focused on spatially homogeneous flows with large-scale tectonic deformations as the main application. Recently, the theory has been extended to spatially varying flows, such as magma with embedded crystals moving through a volcanic plumbing system. Additionally, an evolution equation has been introduced for the probability density function of crystal orientations. Here, we apply this new theory to a number of simple, 2-D flow geometries commonly encountered in magmatic intrusions, such as flow from a dyke into a reservoir or from a reservoir into a dyke, flow inside an inflating or deflating reservoir, flow in a dyke with a sharp bend, and thermal convection in a magma chamber. The main purpose is to provide a guide for interpreting field observations and for setting up more complex flow models with embedded crystals. As a general rule, we find that a larger aspect ratio of the embedded crystals causes a more coherent alignment of the crystals, while it has only a minor effect on the geometry of the alignment pattern. Due to various perturbations in the crystal rotation equations that are expected in natural systems, we show that the time-periodic behaviour found in idealized systems is probably short-lived in nature, and the crystal alignment is well described by the time-averaged solution. We also confirm some earlier findings. For example, near channel walls, fluid flow often follows the bounding surface and the resulting simple shear flow causes preferred crystal orientations that are approximately parallel to the boundary. Where pure shear deformation dominates, there is a tendency for crystals to orient themselves in the direction of the greatest tensile strain rate. Where flow impinges on a boundary, for example in an inflating magma chamber or as part of a thermal convection pattern, the stretching component of pure shear aligns with the boundary, and the crystals orient themselves in that direction. In the field, this local pattern may be difficult to distinguish from a boundary-parallel simple shear flow. Pure shear also dominates along the walls of a deflating magma chamber and in places where the flow turns away from the reservoir walls, but in these locations, the preferred crystal orientation is perpendicular to the wall. Overall, we find that our calculated patterns of crystal orientations agree well with results from analogue experiments where similar geometries are available.

Effects of heat treatments on the microstructure and environment-induced cracking of CF8A steel in simulated BWR water

The effects of heat treatments on the susceptibility to environment-induced cracking (EIC) of the CF8A stainless steel (SS) in simulated water of a boiling water reactor (BWR) were investigated by slow strain-rate tensile (SSRT) tests. Different microstructures were resulted by subjecting the as-casted CF8A to stress relief treatment (1050 °C/2 h, C sample), thermal aging (385 °C/20000 h, A sample), recovery annealing (500 °C/1 h, R sample) or solution annealing (1200 °C/2 h, S sample). The results indicated that after aging treatment (A sample), a decrease in tensile ductility and impact toughness was resulted relative to the un-aged specimens. Recovery annealing (R sample) caused an improved tensile ductility and impact toughness of the embrittled CF8A. Excessive solution (S sample) led to an obvious decrease in tensile strength but increase in ductility and toughness of the CF8A. The EIC susceptibility of the tested samples in simulated BWR water increased in the order: S < C < R < A samples. The cracks in distinct CF8A specimens were found to initiate at and propagate along δ/γ interfaces in simulated BWR water. The lowered ferrite content and change in ferrite morphology accounted for the superior EIC resistance of the S sample relative to that of the other ones in simulated BWR water.

Macroscopic viscoelastic deformation at room temperature in mechanically rejuvenated Zr-based metallic glass

By employing mechanical rejuvenation, we demonstrated that the viscoelastic deformation become visible in macroscopic tensile test. The clear tensile strain rate dependence of yield stress was observed only in the rejuvenated sample, showing that the macroscopic elongation is governed by the thermally activated process. Activation volumes estimated from the mechanical responses during the macroscopic tensile test and microscopic nanoindentation test showed consistent values. The rejuvenated sample having tensile ductility showed larger STZ volume comparing with the relaxed samples. These results indicate that the fraction and connectivity of liquid-like regions in BMG can be controlled by appropriate use of mechanical rejuvenation.

In situ observation of solidification crack propagation for type 310S and 316L stainless steels during TIG welding using synchrotron X-ray imaging

In situ observation of solidification cracking at the weld bead during tungsten inert gas (TIG) welding for type 310S and 316L austenitic stainless steels without the application of an external force was carried out using synchrotron X-ray radiography. The temperature distribution at the weld bead was simultaneously measured using a high-speed camera to directly determine the temperature, in which the propagation of solidification cracking occurred. The solidification cracking was clearly identified and it continuously propagated in the welding direction. The interface of the solidification cracking showed an irregular and zigzag morphology. It was found that the tip velocity of the solidification cracking periodically changed by translating between the high solid fraction (~ 90%) and the relatively lower solid fraction (~ 70%) regions at the centerline of the weld bead for both the type 310S and 316L stainless steels. The solidification cracking propagated at the lower temperature than the solidus temperature due to the segregation of low melting-point components. The tensile strain and strain rate were highly localized in the propagated area every 0.1 s which was the almost same as the time period, in which the tip velocity of the solidification cracking remarkably increased. The periodicity of the solidification cracking velocity at the weld bead can be explained by the dendrite morphology at each solid fraction and strain rate.

7075 알루미늄 합금 판재의 변형률 속도에 따른 고온 인장 파손 거동

7075 알루미늄 합금 판재의 변형률 속도에 따른 고온 인장 파손 거동

Effect of Aging Process on the Strain Rate Sensitivity in V-Containing TWIP Steel

The dynamic tensile behavior of the twinning-induced plasticity (TWIP) steel with the vanadium carbide is investigated at different strain rates of 10−4, 10−3, 10−2 and 0.05 s−1. Microstructure characterization, carried out using back scatter electron diffraction (EBSD) and transmission electron microscopy (TEM), shows a homogeneous face center cubic structured matrix with uniformly dispersed vanadium carbide. The vanadium carbide is controlled by the aging temperature and time. The best comprehensive mechanical properties are achieved when the tested steel is aged at 550 °C for 5 h. With the increase of strain rate, the tensile strength and work hardening rate decrease, and the tested material shows negative strain rate sensitivity. This would be due to an increase in stacking fault energy caused by temperature rise by adiabatic heating, which must suppress the formation of twinning. On the other hand, the strain rate sensitivity is affected by dynamic strain aging (DSA). With the increase of strain rate, the DSA weakens, which causes negative strain rate sensitivity. The tensile strength and strain rate sensitivity value both increase first and then decrease with the increase of vanadium carbide size. This is because the tensile strength is mainly affected by the vanadium carbide. In addition to the vanadium carbide, the strain rate sensitivity is also affected by the amount of solute atom (V and C) during the dynamic strain aging process.

Role of Si Minor Addition on Glass Formation and Flow Stress Characteristics of a Zr-Based Metallic Glass

Abstract The characterization of strain rate effects near glass transition temperature (Tg) gives important information on flow behavior of metallic glasses (MGs). For this purpose, the tensile strain rate jump test was carried out near glass transition temperature to evaluate the flow behaviors of ZrCoAl(Si) MG ribbons. The primary thermal analyses showed that the Si minor addition into the ZrCoAl alloy leads to the betterment of thermal stability and the glass forming ability (GFA), correlated with the small size of Si atoms and subsequent formation of denser atomic clusters and thermodynamically liquid stabilization in the system. The tensile strain rate jump test indicated that minor adding of Si element decreases the sensitivity of glassy alloy to the flow stress and improves the stability of amorphous structure under increase in the strain rate and applied temperature. It was also observed that the viscosity behavior is more stable with the increase of the strain rate and temperature in the Si-added sample, implying the high capability of viscoplastic response in this state.

Mechanical characterization of 3D printed concrete subjected to dynamic loading

In concrete structures realized by digital fabrication techniques, such as 3D concrete printing, under severe dynamic loadings (e.g. earthquakes and impact loads), the strength at the bond interfaces between layers is weak. Since these contact zones, also referred as cold joint, could potentially compromise the structural stability and also the durability of printed elements, their behaviour under high dynamic loads is fundamental to investigate. An experimental program on 3D printed concrete elements varying the waiting time, through medium and high strain-rate tensile tests is running, with a Hydro-Pneumatic Machine and a modified Hopkinson tensile bar respectively. The results of dynamic tensile tests at three different strain rates (10-5, 50 and 200 s-1) on 3D printed cementitious elements for waiting times of 0min, 10min and 30 min have been presented, in terms of Dynamic increase factors DIF versus strain rate, showing a behaviour highly strain-rate sensitive, recording an increase in tensile strength DIF up to 7.6 in the case of high strain-rate and waiting time of 30 min. The results exhibited a decrease in the dynamic interface tensile strength with the waiting time up to over 90% for a medium strain-rate and over 20% for a high strain-rate.

Pearlite-driven surface-cracking and associated loss of tensile ductility in plain-carbon steels under exposure to high-pressure gaseous hydrogen

Four, hot-rolled, plain-carbon steels with varying carbon content were subjected to slow strain-rate tensile (SSRT) tests in a 95-MPa gaseous hydrogen environment at ambient temperature. The influence of pearlite volume fraction on the magnitude of hydrogen-induced degradation of the materials’ strength and ductility was thereby determined. Hydrogen was seen to significantly affect strain-to-failure and reduction-in-area in all four materials, wherein such a loss of tensile ductility was ascribed to the premature initiation and subsequent propagation of surface micro-cracks as revealed by the quantitative damage evolution analyses on the post-fractured specimens. The pearlite grains on sample surfaces manifestly served as the preferential origins of hydrogen-induced micro-cracks, resulting in more considerable embrittlement in materials possessing a higher percentage of pearlite, due to the rapid coalescence of discrete embryonic damage during tensile straining.

Mechanism of hydrogen-induced hardening in pure nickel and in a copper–nickel alloy analyzed by micro Vickers hardness testing

It has often been observed that solute hydrogen triggers a remarkable increase in flow stress in pure Ni. As reported in previous studies, this H-induced hardening has been attributed to the solid-solution strengthening and/or H-enhanced evolution of the dislocation structure. However, it remains unclear which of those two factors actually dominates such macroscopic hardening-behavior. Via two mechanical tests at different scales, i.e. , slow strain-rate tensile (SSRT) and micro Vickers hardness (MVH) tests, the H-enhanced evolution of the dislocation structure and its contribution to H-induced hardening in pure Ni and in Cu–Ni alloy were investigated in this study. In pure Ni, the SSRT test at room temperature (RT) demonstrated an increase in flow stress with a greater work-hardening rate, indicating the H-enhanced evolution of the dislocation structure, as supported by the MVH test. Nevertheless, the SSRT and MVH tests revealed that the H-enhanced evolution of the dislocation structure was significantly suppressed at 77 K. On the other hand, with respect to Cu–Ni alloy, no H-enhanced evolution of dislocation structure was observed during the SSRT and MVH tests, regardless of the deformation temperatures. This difference in the evolution of the dislocation structure between pure Ni and Cu–Ni alloy was consistent with the experimental results obtained beforehand, using scanning transmission electron microscopy (STEM). A series of experimental results indicated that both the solid-solution strengthening and H-enhanced evolution of the dislocation structure could contribute to the increase in flow stress, with the degree of contribution dependent on the respective material and the deformation temperature.