Showing papers on "Strain rate published in 2006"
TL;DR: In this paper, a focused ion beam microscope was used to study single crystal Au columns with diameters ranging from 180'nm to 8'µm. The columns were machined into the surface of a large-grained Au sheet and then mechanically tested using a nanoindenter outfitted with a flat diamond punch.
Abstract: Uniaxial compression tests have been performed on single crystal Au columns ranging in diameter from 180 nm to 8 µm. The columns were machined into the surface of a large-grained Au sheet using a focused ion beam microscope and then mechanically tested using a nanoindenter outfitted with a flat diamond punch. Images of the compressed columns show that deformation occurs by localized shear on the slip systems with the largest resolved shear stresses. After an elastic loading regime, the columns exhibit yielding in discrete strain bursts. The compressive yield stress scales roughly as the inverse square root of the column diameter. The apparent strain hardening rate also increases strongly with decreasing column diameter and stresses as large as 1 GPa are reached. Both of these size effects are attributed to dislocation source-limited behaviour in small volumes.
692 citations
TL;DR: In this paper, a combined experimental and analytical investigation has been performed to understand the mechanical behavior of two amorphous polymers (polycarbonate and poly(methyl methacrylate) at strain rates ranging from 10−4 to 104−s−1.
611 citations
TL;DR: In this paper, a cooperative model based on a strain rate/temperature superposition principle was proposed for compressive yield stress analysis of polycarbonate, polymethylmethacrylate, and polyamideimide.
468 citations
TL;DR: The measured hardness of nanocrystalline Cu with grain sizes as small as 10 nm still follows the Hall-Petch relation as discussed by the authors, suggesting grain boundary activities are enhanced but not yet dominant in the plastic deformation.
456 citations
TL;DR: In this article, the deformation of ultrafine crystalline pure Cu with nanoscale growth twins is analyzed using the twin boundary as an internal interface and allowing special slip geometry arrangements that involve soft and hard modes of deformation.
453 citations
TL;DR: In this article, two different mechanisms for plastic strain-induced grain refinement in pure Cu were identified, corresponding to different levels of strain rate, and the minimum size of refined grains via this process is about 100 nm.
446 citations
TL;DR: In this paper, the deformation kinetics are controlled by the activities of dislocations, and the dominant thermally activated mechanism is suggested to originate from three possible processes, all involving interactions of mobile dislocation with grain boundaries.
416 citations
TL;DR: In this article, the uniaxial compressive responses of silicone rubber (B452 and Sil8800) and pig skin have been measured over a wide range of strain rates (0.004 −4000 s−1).
413 citations
TL;DR: By controlling the specimen aspect ratio and strain rate, compressive strains as high as 80% were obtained in an otherwise brittle metallic glass, and a systematic strain-induced softening was observed which contrasts sharply with the hardening typically observed in crystalline metals.
Abstract: By controlling the specimen aspect ratio and strain rate, compressive strains as high as 80% were obtained in an otherwise brittle metallic glass. Physical and mechanical properties were measured after deformation, and a systematic strain-induced softening was observed which contrasts sharply with the hardening typically observed in crystalline metals. If the deformed glass is treated as a composite of hard amorphous grains surrounded by soft shear-band boundaries, analogous to nanocrystalline materials that exhibit inverse Hall-Petch behavior, the correct functional form for the dependence of hardness on shear-band spacing is obtained. Deformation-induced softening leads naturally to shear localization and brittle fracture.
390 citations
TL;DR: In this paper, the rate-dependent stress-strain behavior of one polyurea and three representative polyurethane materials is studied by dynamic mechanical analysis, quasi-static compression testing and split Hopkinson pressure bar (SHPB) testing.
371 citations
TL;DR: Weerheijm et al. as mentioned in this paper used free surface velocity at the end of a cylindrical concrete sample to measure the tensile strength and specific fracture energy in spall experiments.
TL;DR: In this article, the effect of deformation twinning on the strain hardening behavior of polycrystalline AM30 Mg alloy was investigated, and the softening effect induced by double and contraction twinning was responsible for the abnormal strain-hardening behavior.
TL;DR: In this article, a series of both quasi-static and dynamic uniaxial compression tests on cylindrical samples, using an Instron servohydraulic testing machine and UCSD's enhanced Hopkinson technique, were performed, at initial temperatures in the range of 77-400 K.
TL;DR: In this article, the compressive mechanical behavior of three common polymeric foams (expanded polystyrene, high-density polyethylene, and polyurethane) has been measured at strain rates ranging from 0.0087 to 2500/s.
TL;DR: Tracer and particle-tracking experiments show that molecular stretching produces two flow instabilities: one in which the velocity field becomes strongly asymmetric, and a second in which it fluctuates nonperiodically in time.
Abstract: When polymer molecules pass near the hyperbolic point of a microchannel cross flow, they are strongly stretched. As the strain rate is varied at low Reynolds number (< 10(-2)), tracer and particle-tracking experiments show that molecular stretching produces two flow instabilities: one in which the velocity field becomes strongly asymmetric, and a second in which it fluctuates nonperiodically in time. The flow is strongly perturbed even far from the region of instability, and this phenomenon can be used to produce mixing.
TL;DR: In this article, the results of laboratory tests on the time-dependent behaviour of three argillaceous rocks characterized by a high proportion of clay particles were presented, and the authors highlighted the significant viscoplasticity of these sedimentary rocks.
TL;DR: An analytic expression for the strengthening versus strain rate and temperature that justifies widely used phenomenological forms is derived, and the predicted strengthening quantitatively agrees with the experimentally derived behaviour of Al–2.5% Mg at 300 K.
Abstract: Dynamic strain ageing (DSA) is the phenomenon in which solute atoms diffuse around dislocations and retard dislocation motion, leading to negative strain-rate sensitivity (nSRS) and thus to material instabilities during processing, an important issue in commercial metal alloys. Here, we show the mechanism of DSA and nSRS on experimental strain-rate, temperature and stress scales for Al-Mg to be single-atomic-hop motion of solutes from the compression to the tension side of a dislocation core. We derive an analytic expression for the strengthening versus strain rate and temperature that justifies widely used phenomenological forms, provides specific dependences of the parameters on material properties and is supported by atomistic kinetic Monte Carlo simulations. Using literature material properties, the predicted strengthening quantitatively agrees with the experimentally derived behaviour of Al-2.5% Mg at 300 K, and qualitatively agrees with the strain rate and temperature ranges of DSA and nSRS in Al-Mg alloys. The analyses herein show a clear path for multiscale design, from quantum to continuum mechanics, of solute strengthening in face-centred-cubic metal alloys.
TL;DR: In this article, a 3D model of viscoplastic flow and temperature field during friction stir welding (FSW) of 304 austenitic stainless steel were mathematically modelled using spatially variable thermophysical properties using a methodology adapted from well established previous work in fusion welding.
Abstract: Three-dimensional (3D) viscoplastic flow and temperature field during friction stir welding (FSW) of 304 austenitic stainless steel were mathematically modelled. The equations of conservation of mass, momentum and energy were solved in three dimensions using spatially variable thermophysical properties using a methodology adapted from well established previous work in fusion welding. Non-Newtonian viscosity for the metal flow was calculated considering strain rate and temperature dependent flow stress. The computed profiles of strain rate and viscosity were examined in light of the existing literature on thermomechanical processing of alloys. The computed results showed significant viscoplastic flow near the tool surface, and convective transport of heat was found to be an important mechanism of heat transfer. The computed temperature and velocity fields demonstrated strongly 3D nature of the transport of heat and mass indicating the need for 3D calculations. The computed temperature profiles agreed well with the corresponding experimentally measured values. The non-Newtonian viscosity for FSW of stainless steel was found to be of the same order of magnitude as that for the FSW of aluminium. Like FSW of aluminium, the viscosity was found to be a strong function of both strain rate and temperature, while strain rate was found to be the most dominant factor. A small region of recirculating plasticised material was found to be present near the tool pin. The size of this region was larger near the shoulder and smaller further away from it. Streamlines around the pin were influenced by the presence of the rotating shoulder, especially at higher elevations. Stream lines indicated that material was transported mainly around the pin in the retreating side.
TL;DR: In this paper, the effect of strain rate on stress-strain behavior of austenitic stainless steel 309 and 304L was investigated, where tensile tests were conducted at room temperature at strain rates ranging from 1.25×10−4s−1 to 400 s−1.
Abstract: The effect of strain rate on stress-strain behavior of austenitic stainless steel 309 and 304L was investigated. Tensile tests were conducted at room temperature at strain rates ranging from 1.25×10−4s−1 to 400 s−1. The evolution of volume fraction martensite that formed during plastic deformation was measured with X-ray diffraction and characterized with light microscopy. Alloy 304L was found to transform readily with strain, with martensite nucleating on slip bands and at slip band intersections. Alloy 309 did not exhibit strain-induced transformation. Variations in ductility and strength with strain rate are explained in terms of the competition between hardening, from the martensitic transformation and a positive strain rate sensitivity, and softening due to deformational heating. Existing models used to predict the increase in volume fraction martensite with strain were examined and modified to fit the experimental data of this study as well as recent data for alloys 304 and 301LN obtained from the literature.
TL;DR: The atomistic response of a model amorphous material submitted to plastic shear in the athermal, quasi-static limit is analyzed in detail, showing a hyper-diffusive regime followed by a diffusive regime, even at zero temperature.
Abstract: We analyze in detail the atomistic response of a model amorphous material submitted to plastic shear in the athermal, quasi-static limit. After a linear stress-strain behavior, the system undergoes a noisy plastic flow. We show that the plastic flow is spatially heterogeneous. Two kinds of plastic events occur in the system: quadrupolar localized rearrangements, and shear bands. The analysis of the individual motion of a particle shows also two regimes: a hyper-diffusive regime followed by a diffusive regime, even at zero temperature.
TL;DR: In this article, a servo-hydraulic testing machine was used to study the strain-rate dependent behavior of concrete in tension and the effect of temperature and moisture content on the strain sensitivity of concrete.
TL;DR: In this paper, a constitutive model of finite strain viscoelasticity based on the multiplicative decomposition of the deformation gradient tensor into elastic and inelastic parts is proposed.
TL;DR: In this paper, deformation-induced phase transformation in a type 304 austenitic stainless steel has been studied in tension at room temperature and −50 °C. The evolution of transformation products was monitored using X-ray diffraction (XRD) line profile analysis of diffraction peaks from a single XRD scan employing the direct comparison method.
Abstract: Deformation-induced phase transformation in a type 304 austenitic stainless steel has been studied in tension at room temperature and −50 °C. The evolution of transformation products was monitored using X-ray diffraction (XRD) line profile analysis of diffraction peaks from a single XRD scan employing the direct comparison method. Crystallographic texture transitions due to deformation strain have been evaluated using (111)
γ
pole figures. The tensile stress-strain data have been analyzed to explain the influence of underlying deformation-induced microstructural changes and associated texture changes in the steel. It is found that the initial stage of rapidly decreasing strain hardening rate in type 304 steel is primarily influenced by hcp ɛ-martensite formation, and the second stage of increasing strain hardening rate is associated with an increase in the α′-martensite formation. The formation of ɛ-martensite is associated with a gradual strengthening of the copper-type texture components up to 15 pct strain and decreasing with further strain at −50 °C. Texture changes during low-temperature deformation not only change the mechanism of ɛ-martensite formation but also influence the strain rate sensitivity of the present steel.
TL;DR: The results of the present work indicated that MVAL tissues exhibit complete strain rate insensitivity at and below physiological strain rates under physiological loading conditions, suggesting that experimental tests utilizing quasi-static strain rates are appropriate for constitutive model development for mitral valve tissues.
Abstract: Characterization of the mechanical properties of the native mitral valve leaflets at physiological strain rates is a critical step in improving our understanding of MV function and providing experimental data for dynamic constitutive models. We explored, for the first time, the effects of strain rate (from quasi-static to physiologic) on the biaxial mechanical properties of the native mitral valve anterior leaflet (MVAL). A novel high-speed biaxial testing device was developed, capable of achieving in vitro strain rates reported for the MVAL (Sacks et al., Ann. Biomed. Eng. 30(10):1280–1290, 2002). Porcine MVAL specimens were loaded to physiological load levels with cycle periods of 15, 1, 0.5, 0.1, and 0.05 s. The resulting loading stress–strain responses were found to be remarkably independent of strain rate. The hysteresis, defined as the fraction of the membrane strain energy between the loading and unloading curves tension-areal stretch curves, was low (∼12%) and did not vary with strain rate. The results of the present work indicated that MVAL tissues exhibit complete strain rate insensitivity at and below physiological strain rates under physiological loading conditions. These novel results suggest that experimental tests utilizing quasi-static strain rates are appropriate for constitutive model development for mitral valve tissues. The mechanisms underlying this quasi-elastic behavior are as yet unknown, but are likely an important functional aspect of native mitral valve tissues and clearly warrant further study.
TL;DR: In this article, the effects of loading rate, peak/valley strain or stress holds, ambient temperature and non-proportional loading path on the cyclic softening/hardening and ratchetting behaviors of the material were discussed.
Journal Article•
TL;DR: In this paper, an improved method for rotational shear experiments is used, producing an approximately homogeneous strain field and leading to an enhanced accuracy. But the results of these experiments were limited to the case of porcine brain tissue, and no significant immediate damage was observed for these shear deformations up to strains of 0.45.
TL;DR: In this paper, a constitutive material law with a damping controlled glide process was used to describe the material flow behavior of the tested alloys under high strain rates loading with the assumption of domination of damping control.
TL;DR: In this paper, the critical stress for initiation of dynamic recrystallization (DRX) can be identified from the inflection point on the strain hardening rate (qds/de) versus flow stress (s) curve.
Abstract: The critical stress for initiation of dynamic recrystallization (DRX) can be identified from the inflection point on the strain hardening rate (qds/de) versus flow stress (s) curve. This kind of curve can be described by an equation that fits the experimental q-s data from zero to the peak stress. Such a curve must have an in- flection point and the simplest relation that has such properties is a third order equation. Hot compression tests were carried out on a 304 H stainless steel over the temperature range 900-1 100°C and strain rate range 0.01-1 s � 1 to a strain of 1. An appropriate third order equation was fitted to the strain hardening data. The results show that the critical stress at initiation s c�� B/3A where A and B are coefficients of the third order equation. It is evident that this value depends on the deformation condi- tions. The stress-strain curve was then normalized with respect to the peak stress, leading to a normalized value of the critical stress (uc) equal to ucs c/s p�� B� /3A� . Here Aand Bare coefficients of the normal- ized third order equation. This value is constant and independent of the deformation conditions.
TL;DR: In this paper, the authors performed tensile tests on cylindrical specimens made of wet and dry concrete with different strain rates from 10 s−1 to 120 s−s−1 by means of a special experimental technique.
TL;DR: A constrained dynamic free-vibration phenomenon is observed during stretching, which eventually leads to delocalized multiple necking, instead of a single localized neck when it is strained at a lower rate.
Abstract: Current computational simulations on metallic nanowires are largely focused on ultrathin wires with characteristic sizes smaller than 2 nm. The electronic, thermal and optical properties form the bulk of these studies, with investigations of the mechanical properties centred on the breaking force of monatomic chains, and the structural evolution of small nanowires subjected to axial, shear, bending and torsional forces. This study seeks to build on the wealth of current knowledge for computational simulation on the mechanical properties of metallic nanowires. The simulation scale will be upped to 24 000 atoms to study a larger metallic nanowire with a 6 nm characteristic size scale. The commonly studied Au nanowire is studied in conjunction with the rarely examined Pt nanowire. The effects that size and strain rate have on the stretching behaviour of these nanowires are investigated through the simulation of nanowires with three characteristic sizes of 2, 4 and 6 nm, subjected to three distinct strain rates of 4.0 x 10(8), 4.0 x 10(9) and 4.0 x 10(10) s(-1). The selected strain rates produce three distinct modes of deformation, namely crystalline-ordered deformation, mixed-mode deformation and amorphous-disordered deformation, respectively. The mechanisms behind the observations of these distinct deformation modes are analysed and explained. A Doppler 'red-shift' effect is observed when the nanowires are strained at the highest strain rate of 4.0 x 10(10) s(-1). This effect is most pronounced for the nanowire subjected to the largest stretch velocity. As a result, a constrained dynamic free-vibration phenomenon is observed during stretching, which eventually leads to delocalized multiple necking, instead of a single localized neck when it is strained at a lower rate. This unique phenomenon is discussed and future research effort is in the pipeline for a more detailed investigation into metallic nanowires strained at a supersonic velocity.