WorldWideScience

Sample records for plastic strain rate

  1. Strain rate dependence in plasticized and un-plasticized PVC

    Directory of Open Access Journals (Sweden)

    Siviour C.R.

    2012-08-01

    Full Text Available An experimental and analytical investigation has been made into the mechanical behaviour of two poly (vinyl chloride (PVC polymers – an un-plasticized PVC and a diisononyl phthalate (DINP-plasticized PVC. Measurements of the compressive stress-strain behaviour of the PVCs at strain rates ranging from 10−3 to 103s−1 and temperatures from − 60 to 100∘C are presented. Dynamic Mechanical Analysis was also performed in order to understand the material transitions observed in compression testing as the strain rate is increased. This investigation develops a better understanding of the interplay between the temperature dependence and rate dependence of polymers, with a focus on locating the temperature and rate-dependent material transitions that occur during high rate testing.

  2. Strain rate dependence in plasticized and un-plasticized PVC

    Science.gov (United States)

    Kendall, M. J.; Siviour, C. R.

    2012-08-01

    An experimental and analytical investigation has been made into the mechanical behaviour of two poly (vinyl chloride) (PVC) polymers - an un-plasticized PVC and a diisononyl phthalate (DINP)-plasticized PVC. Measurements of the compressive stress-strain behaviour of the PVCs at strain rates ranging from 10-3 to 103s-1 and temperatures from - 60 to 100∘C are presented. Dynamic Mechanical Analysis was also performed in order to understand the material transitions observed in compression testing as the strain rate is increased. This investigation develops a better understanding of the interplay between the temperature dependence and rate dependence of polymers, with a focus on locating the temperature and rate-dependent material transitions that occur during high rate testing.

  3. High strain rate loading of polymeric foams and solid plastics

    Science.gov (United States)

    Dick, Richard D.; Chang, Peter C.; Fourney, William L.

    2000-04-01

    The split-Hopkinson pressure bar (SHPB) provided a technique to determine the high strain rate response for low density foams and solid ABS and polypropylene plastics. These materials are used in the interior safety panels of automobiles and crash test dummies. Because the foams have a very low impedance, polycarbonate bars were used to acquire the strain rate data in the 100 to 1600 l/s range. An aluminum SPHB setup was used to obtain the solid plastics data which covered strain rates of 1000 to 4000 l/s. The curves for peak strain rate versus peak stress for the foams over the test range studied indicates only a slight strain rate dependence. Peak strain rate versus peak stress curves for polypropylene shows a strain rate dependence up to about 1500 l/s. At that rate the solid poly propylene indicates no strain rate dependence. The ABS plastics are strain rate dependent up to 3500 l/s and then are independent at larger strain rates.

  4. Attaining the rate-independent limit of a rate-dependent strain gradient plasticity theory

    DEFF Research Database (Denmark)

    El-Naaman, Salim Abdallah; Nielsen, Kim Lau; Niordson, Christian Frithiof

    2016-01-01

    The existence of characteristic strain rates in rate-dependent material models, corresponding to rate-independent model behavior, is studied within a back stress based rate-dependent higher order strain gradient crystal plasticity model. Such characteristic rates have recently been observed...... for steady-state processes, and the present study aims to demonstrate that the observations in fact unearth a more widespread phenomenon. In this work, two newly proposed back stress formulations are adopted to account for the strain gradient effects in the single slip simple shear case, and characteristic...

  5. Gurson-type elastic-plastic damage model based on strain-rate plastic potential

    Science.gov (United States)

    Balan, Tudor; Cazacu, Oana

    2013-12-01

    Ductile damage is generally described by stress-space analytical potentials. In this contribution, it is shown that strain rate potentials, which are exact conjugate of the stress-based potentials, can be equally used to describe the dilatational response of porous metals. This framework is particularly appropriate for porous materials with matrix described by complex yield criteria for which a closed-form expression of the stress-based potential is not available. Illustration of the new approach is done for porous metals containing randomly distributed spherical voids in a von Mises elasto-plastic matrix. Furthermore, a general time integration algorithm for simulation of the mechanical response using this new formulation is developed and implemented in Abaqus/Standard. The proposed model and algorithm are validated with respect to the Abaqus built-in GTN model, which is based on a stress potential, through the simulation of a tensile test on a round bar.

  6. A numerical basis for strain-gradient plasticity theory: Rate-independent and rate-dependent formulations

    DEFF Research Database (Denmark)

    Nielsen, Kim Lau; Niordson, Christian Frithiof

    2014-01-01

    of a single plastic zone is analyzed to illustrate the agreement with earlier published results, whereafter examples of (ii) multiple plastic zone interaction, and (iii) elastic–plastic loading/unloading are presented. Here, the simple shear problem of an infinite slab constrained between rigid plates......–plastic loading/unloading and the interaction of multiple plastic zones, is proposed. The predicted model response is compared to the corresponding rate-dependent version of visco-plastic origin, and coinciding results are obtained in the limit of small strain-rate sensitivity. First, (i) the evolution...

  7. PLASTIC DEFORMATION BEHAVIOR OF ELECTROFORMED COPPER LINER OF SHAPED CHARGE AT DIFFERENT STRAIN RATES

    Institute of Scientific and Technical Information of China (English)

    H.Y.Gao; Q.Sun

    2003-01-01

    The paper deals with different plastic deformation behavior of electroformed copper liner of shaped charge,depormed at high strain rate(about 1×107s-1) and normal strain rate (4×10-4s-1).The crystallographic orientation distribution of grains in recovered slugs which had undergone high-strain-rate plastic deformation during ex-plosive detonation was investigated by electron backscattering Kikuchi pattern tech-nique.Cellualar structures formed by tangled disocations and sub-grain boundaries consisting of dislocation arrays were detected in the recovered slugs.Some twins and slip dislocations were observed in specimen deformed at normal strain rate.It was found that dynamic recovery and recrystallization take place during high-strain-rate deformation due to the temperature rising,whereas the conventional slip mechanism operates during deformation at normal strain rate.

  8. Suppression of dislocations at high strain rate deformation in a twinning-induced plasticity steel

    Energy Technology Data Exchange (ETDEWEB)

    Liang, Z.Y. [Shenzhen Institute of Research and Innovation, The University of Hong Kong, Shenzhen (China); Department of Mechanical Engineering, The University of Hong Kong, Hong Kong (China); Huang, W., E-mail: whuang@szu.edu.cn [Department of Civil Engineering, Shenzhen University, Shenzhen (China); Huang, M.X., E-mail: mxhuang@hku.hk [Shenzhen Institute of Research and Innovation, The University of Hong Kong, Shenzhen (China); Department of Mechanical Engineering, The University of Hong Kong, Hong Kong (China)

    2015-03-25

    The increase of strain rate generally enhances dislocation evolution in face-centred cubic (FCC) metals. However, by synchrotron X-ray diffraction experiments, the present work demonstrates for the first time that a higher strain rate leads to a lower dislocation density in a twinning-induced plasticity steel with an FCC structure. This unexpected suppression of dislocation evolution has been attributed to the temperature increase due to dissipative heating at high strain rate deformation.

  9. Effect of transient change in strain rate on plastic flow behaviour of low carbon steel

    Indian Academy of Sciences (India)

    A Ray; P Barat; P Mukherjee; A Sarkar; S K Bandyopadhyay

    2007-02-01

    Plastic flow behaviour of low carbon steel has been studied at room temperature during tensile deformation by varying the initial strain rate of 3.3 × 10-4 s-1 to a final strain rate ranging from 1.33 × 10-3 s-1 to 2 × 10-3 s-1 at a fixed engineering strain of 12%. Haasen plot revealed that the mobile dislocation density remained almost invariant at the juncture where there was a sudden increase in stress with a change in strain rate and the plastic flow was solely dependent on the velocity of mobile dislocations. In that critical regime, the variation of stress with time was fitted with a Boltzmann type Sigmoid function. The increase in stress was found to increase with final strain rate and the time elapsed in attaining these stress values showed a decreasing trend. Both of these parameters saturated asymptotically at a higher final strain rate.

  10. Response of Polypmeric Foams and ABS Plastics to High Strain Rate Loading

    Science.gov (United States)

    Dick, Richard; Chang, Peter; Fourney, William

    1999-06-01

    The split-Hopkinson pressure bar (SHPB) technique was utilized to obtain high strain rate response data for low-density foams and solid ABS and polypropylene plastics. General Motors provided the materials for this study. These materials are used in the interior panels of automobiles. Because the foams have a very low impedance, polycarbonate bars were used to acquire the strain rate data in the 100 to 1600 per second range. An aluminum SHPB was used to obtain the solid plastics data that covered strain rates of 1000 to 4000 pre second. The experimental data indicate that the foams over the test range are only slightly strain rate dependent while the polypropylene appears to be strain rate independent above 1000 per second and the ABS plastics are strain rate independent above 3000 per second. The projectile length was varied to provide a wide range of induced strains ranging from 10 to 70 per cent for the foams and up to 20 per cent for the plastic materials.

  11. PLASTIC DEFORMATION BEHAVIOR OF ELECTROFORMED COPPER LINER OF SHAPED CHARGE AT DIFFERENT STRAIN RATES

    Institute of Scientific and Technical Information of China (English)

    H.Y. Gao; W.H. Tian; A.L. Fan; Q. Sun

    2003-01-01

    The paper deals with different plastic deformation behavior of electroformed copperliner of shaped charge, deformed at high strain rate (about 1×107 s-1) and normalstrain rate (4×10-4 s-1). The crystallographic orientation distribution of grains inrecovered slugs which had undergone high-strain-rate plastic deformation during ex-plosive detonation was investigated by electron backscattering Kikuchi pattern tech-nique. Cellular structures formed by tangled dislocations and sub-grain boundariesconsisting of dislocation arrays were detected in the recovered slugs. Some twins andslip dislocations were observed in specimen deformed at normal strain rate. It wasfound that dynamic recovery and recrystallization take place during high-strain-ratedeformation due to the temperature rising, whereas the conventional slip mechanismoperates during deformation at normal strain rate.

  12. Modelling plastic deformation of metals over a wide range of strain rates using irreversible thermodynamics

    NARCIS (Netherlands)

    Huang, M.; Rivera-Diaz-del-Castillo, P.E.J.; Bouaziz, O.; Van der Zwaag, S.

    2009-01-01

    Based on the theory of irreversible thermodynamics, the present work proposes a dislocation-based model to describe the plastic deformation of FCC metals over wide ranges of strain rates. The stress-strain behaviour and the evolution of the average dislocation density are derived. It is found that t

  13. The Microstructure Evolution of Dual-Phase Pipeline Steel with Plastic Deformation at Different Strain Rates

    Science.gov (United States)

    Ji, L. K.; Xu, T.; Zhang, J. M.; Wang, H. T.; Tong, M. X.; Zhu, R. H.; Zhou, G. S.

    2017-07-01

    Tensile properties of the high-deformability dual-phase ferrite-bainite X70 pipeline steel have been investigated at room temperature under the strain rates of 2.5 × 10-5, 1.25 × 10-4, 2.5 × 10-3, and 1.25 × 10-2 s-1. The microstructures at different amount of plastic deformation were examined by using scanning and transmission electron microscopy. Generally, the ductility of typical body-centered cubic steels is reduced when its stain rate increases. However, we observed a different ductility dependence on strain rates in the dual-phase X70 pipeline steel. The uniform elongation (UEL%) and elongation to fracture (EL%) at the strain rate of 2.5 × 10-3 s-1 increase about 54 and 74%, respectively, compared to those at 2.5 × 10-5 s-1. The UEL% and EL% reach to their maximum at the strain rate of 2.5 × 10-3 s-1. This phenomenon was explained by the observed grain structures and dislocation configurations. Whether or not the ductility can be enhanced with increasing strain rates depends on the competition between the homogenization of plastic deformation among the microconstituents (ultra-fine ferrite grains, relatively coarse ferrite grains as well as bainite) and the progress of cracks formed as a consequence of localized inconsistent plastic deformation.

  14. Dynamic recrystallization of electroformed copper liners of shaped charges in high-strain-rate plastic deformation

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The microstructures in the electroformed copper liners of shaped charges after high-strain-rate plastic deformation were investigated by transmission electron microscopy (TEM). Meanwhile, the orientation distribution of the grains in the recovered slug was examined by the electron backscattering Kikuchi pattern (EBSP) technique. EBSP analysis illustrated that unlike the as-formed electroformed copper linersof shaped charges the grain orientations in the recovered slug are distributed along randomly all the directions after undergoing heavily strain deformation at high-strain rate. Optical microscopy shows a typical recrystallization structure, and TEM examination reveals dislocation cells existed in the thin foil specimen. These results indicate that dynamic recovery and recrystallization occur during this plastic deformation process, and the associated deformation temperature is considered to be higher than 0.6 times the melting point of copper.

  15. Hardening in Two-Phase Materials. II. Plastic Strain and Mean Stress Hardening Rate

    DEFF Research Database (Denmark)

    Lilholt, Hans

    1977-01-01

    The strain parameters which are relevant in a tensile experiment, are analysed and related to the geometry of deformation and to the mean stress of two-phase materials. The hardening rate of the mean stress with respect to plastic strain is found to be useful in comparison between experiments and...... and theories, and it allows theories to be probed over a range of strains. Previous experiments on the fibre-reinforced material of copper-tungsten are analysed in relation to the geometry of deformation....

  16. Modelling plastic deformation of metals over a wide range of strain rates using irreversible thermodynamics

    Energy Technology Data Exchange (ETDEWEB)

    Huang Mingxin; Rivera-Diaz-del-Castillo, Pedro E J; Zwaag, Sybrand van der [Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS, Delft (Netherlands); Bouaziz, Olivier, E-mail: mingxin.huang@arcelormittal.com [ArcelorMittal Maizieres, Research and Development, Voie Romaine-BP30320, 57283 Maizieres-les-Metz Cedex (France)

    2009-07-15

    Based on the theory of irreversible thermodynamics, the present work proposes a dislocation-based model to describe the plastic deformation of FCC metals over wide ranges of strain rates. The stress-strain behaviour and the evolution of the average dislocation density are derived. It is found that there is a transitional strain rate ({approx} 10{sup 4} s{sup -1}) over which the phonon drag effects appear, resulting in a significant increase in the flow stress and the average dislocation density. The model is applied to pure Cu deformed at room temperature and at strain rates ranging from 10{sup -5} to 10{sup 6} s{sup -1} showing good agreement with experimental results.

  17. Grain-size-independent plastic flow at ultrahigh pressures and strain rates.

    Science.gov (United States)

    Park, H-S; Rudd, R E; Cavallo, R M; Barton, N R; Arsenlis, A; Belof, J L; Blobaum, K J M; El-dasher, B S; Florando, J N; Huntington, C M; Maddox, B R; May, M J; Plechaty, C; Prisbrey, S T; Remington, B A; Wallace, R J; Wehrenberg, C E; Wilson, M J; Comley, A J; Giraldez, E; Nikroo, A; Farrell, M; Randall, G; Gray, G T

    2015-02-13

    A basic tenet of material science is that the flow stress of a metal increases as its grain size decreases, an effect described by the Hall-Petch relation. This relation is used extensively in material design to optimize the hardness, durability, survivability, and ductility of structural metals. This Letter reports experimental results in a new regime of high pressures and strain rates that challenge this basic tenet of mechanical metallurgy. We report measurements of the plastic flow of the model body-centered-cubic metal tantalum made under conditions of high pressure (>100  GPa) and strain rate (∼10(7)  s(-1)) achieved by using the Omega laser. Under these unique plastic deformation ("flow") conditions, the effect of grain size is found to be negligible for grain sizes >0.25  μm sizes. A multiscale model of the plastic flow suggests that pressure and strain rate hardening dominate over the grain-size effects. Theoretical estimates, based on grain compatibility and geometrically necessary dislocations, corroborate this conclusion.

  18. High-rate Plastic Deformation of Nanocrystalline Tantalum to Large Strains: Molecular Dynamics Simulation

    Energy Technology Data Exchange (ETDEWEB)

    Rudd, R E

    2009-02-05

    Recent advances in the ability to generate extremes of pressure and temperature in dynamic experiments and to probe the response of materials has motivated the need for special materials optimized for those conditions as well as a need for a much deeper understanding of the behavior of materials subjected to high pressure and/or temperature. Of particular importance is the understanding of rate effects at the extremely high rates encountered in those experiments, especially with the next generation of laser drives such as at the National Ignition Facility. Here we use large-scale molecular dynamics (MD) simulations of the high-rate deformation of nanocrystalline tantalum to investigate the processes associated with plastic deformation for strains up to 100%. We use initial atomic configurations that were produced through simulations of solidification in the work of Streitz et al [Phys. Rev. Lett. 96, (2006) 225701]. These 3D polycrystalline systems have typical grain sizes of 10-20 nm. We also study a rapidly quenched liquid (amorphous solid) tantalum. We apply a constant volume (isochoric), constant temperature (isothermal) shear deformation over a range of strain rates, and compute the resulting stress-strain curves to large strains for both uniaxial and biaxial compression. We study the rate dependence and identify plastic deformation mechanisms. The identification of the mechanisms is facilitated through a novel technique that computes the local grain orientation, returning it as a quaternion for each atom. This analysis technique is robust and fast, and has been used to compute the orientations on the fly during our parallel MD simulations on supercomputers. We find both dislocation and twinning processes are important, and they interact in the weak strain hardening in these extremely fine-grained microstructures.

  19. Interaction of heat production, strain rate and stress power in a plastically deforming body under tensile test

    Science.gov (United States)

    Paglietti, A.

    1982-01-01

    At high strain rates the heat produced by plastic deformation can give rise to a rate dependent response even if the material has rate independent constitutive equations. This effect has to be evaluated when interpreting a material test, or else it could erroneously be ascribed to viscosity. A general thermodynamic theory of tensile testing of elastic-plastic materials is given in this paper; it is valid for large strain at finite strain rates. It enables discovery of the parameters governing the thermodynamic strain rate effect, provides a method for proper interpretation of the results of the tests of dynamic plasticity, and suggests a way of planning experiments in order to detect the real contribution of viscosity.

  20. Interaction of heat production, strain rate and stress power in a plastically deforming body under tensile test

    Science.gov (United States)

    Paglietti, A.

    1982-01-01

    At high strain rates the heat produced by plastic deformation can give rise to a rate dependent response even if the material has rate independent constitutive equations. This effect has to be evaluated when interpreting a material test, or else it could erroneously be ascribed to viscosity. A general thermodynamic theory of tensile testing of elastic-plastic materials is given in this paper; it is valid for large strain at finite strain rates. It enables discovery of the parameters governing the thermodynamic strain rate effect, provides a method for proper interpretation of the results of the tests of dynamic plasticity, and suggests a way of planning experiments in order to detect the real contribution of viscosity.

  1. Multi-Layer Strain Rate Field Controlled by Netlike Plastic-Flow in the Lithosphere in Central-Eastern Asia

    Institute of Scientific and Technical Information of China (English)

    Wang Sheng-zu

    2006-01-01

    According to the "Netlike Plastic-Flow (NPF)" continental dynamics model, the transition of the deformation regime from brittle in shallow layers to ductile in deep layers in the lithosphere, and the controlling effect of NPF in the lower lithosphere result in intraplate multilayer tectonic deformation. NPF is a viscous (plastic) flow accompanied by shear strain localization, forming a plastic-flow network in the lower lithosphere. The strain rates in the seismogenic layer can be estimated using the "earthquake-recurrence-interval" method, in which the strain rate is calculated in terms of the recurrence interval of two sequential carthquakes and the seismic probability of the second earthquake. The strains in the lower lithosphere are estimated using the "conjugate-angle" method, which takes the relationship between the conjugate angles and the compressive strains of the network, and calculates the characteristic strain rates in this layer from the strains and the durations of deformation inferred. The contour map of characteristic maximum principal compressive strain rates in the lower lithosphere in central-eastern Asia given in the paper shows strain rates with magnitudes on the order of 10-15 ~ 10-14/s in this region. The strain rates within the plastic-flow belts,which control seismic activities in the seismogenic layer, are greater than the characteristic strain rates of the network and, in addition, the strain rates and seismic activities in the seismogenic layer are also influenced by other factors, including the directive action of driving boundary along the upper crust, the effects of plastic-flow waves and the existence of the transitional weak layer distributed discontinuously between the upper and lower layers. The comparison between the strain rates in the seismogenic layer and the characteristic strain rates in the lower lithosphere for 11 potential hypocenter areas in the region from the Qinghai-Xizang (Tibet) plateau to the North China plain

  2. PLASTICITY AND NON-LINEAR ELASTIC STRAINS

    Science.gov (United States)

    conditions existing in plane waves in an extended medium to give the time rate of change of stress as a function of the time rate of change of strain, the stress invariants, the total strain and the plastic strain. (Author)

  3. Numerical implementation of a crystal plasticity model with dislocation transport for high strain rate applications

    Science.gov (United States)

    Mayeur, Jason R.; Mourad, Hashem M.; Luscher, Darby J.; Hunter, Abigail; Kenamond, Mark A.

    2016-05-01

    This paper details a numerical implementation of a single crystal plasticity model with dislocation transport for high strain rate applications. Our primary motivation for developing the model is to study the influence of dislocation transport and conservation on the mesoscale response of metallic crystals under extreme thermo-mechanical loading conditions (e.g. shocks). To this end we have developed a single crystal plasticity theory (Luscher et al (2015)) that incorporates finite deformation kinematics, internal stress fields caused by the presence of geometrically necessary dislocation gradients, advection equations to model dislocation density transport and conservation, and constitutive equations appropriate for shock loading (equation of state, drag-limited dislocation velocity, etc). In the following, we outline a coupled finite element-finite volume framework for implementing the model physics, and demonstrate its capabilities in simulating the response of a [1 0 0] copper single crystal during a plate impact test. Additionally, we explore the effect of varying certain model parameters (e.g. mesh density, finite volume update scheme) on the simulation results. Our results demonstrate that the model performs as intended and establishes a baseline of understanding that can be leveraged as we extend the model to incorporate additional and/or refined physics and move toward a multi-dimensional implementation.

  4. Effects of Strain Rate and Plastic Work on Martensitic Transformation Kinetics of Austenitic Stainless Steel 304

    Institute of Scientific and Technical Information of China (English)

    Fang PENG; Xiang-huai DONG; Kai LIU; Huan-yang XIE

    2015-01-01

    The martensitic transformation behavior and mechanical properties of austenitic stainless steel 304 were studied by both experiments and numerical simulation. Room temperature tensile tests were carried out at various strain rates to investigate the effect on volume fraction of martensite, temperature increase and flow stress. The results show that with increasing strain rate, the local temperature increases, which suppresses the transformation of martensite. To take into account the dependence on strain level, strain rate sensitivity and thermal effects, a kinetic model of martensitic transformation was proposed and constitutive modeling on stress-strain response was conducted. The validity of the proposed model has been proved by comparisons between simulation results and experimental ones.

  5. SOME MISUNDERSTANDINGS ON ROTATION OF CRYSTALS AND REASONABLE PLASTIC STRAIN RATE

    Institute of Scientific and Technical Information of China (English)

    赵祖武

    2001-01-01

    It is pointed out that crystals are discrete but not continuous materials. Hence the rotation R in decomposition F = RU and spin W in F F-1 are not correct. Errors will arise in plastic deformation rate if it is directly expressed with amounts of velocity of slips in glide systems such as γv n . The geometrical figure of crystal lattices does not change after slips and based on this idea a simple way in mechanics of continuous media to get the plastic deformations rate induced by slips is proposed. Constitutive equations are recommended.

  6. A model for plasticity kinetics and its role in simulating the dynamic behavior of Fe at high strain rates

    Energy Technology Data Exchange (ETDEWEB)

    Colvin, J D; Minich, R W; Kalantar, D H

    2007-03-29

    The recent diagnostic capability of the Omega laser to study solid-solid phase transitions at pressures greater than 10 GPa and at strain rates exceeding 10{sup 7} s{sup -1} has also provided valuable information on the dynamic elastic-plastic behavior of materials. We have found, for example, that plasticity kinetics modifies the effective loading and thermodynamic paths of the material. In this paper we derive a kinetics equation for the time-dependent plastic response of the material to dynamic loading, and describe the model's implementation in a radiation-hydrodynamics computer code. This model for plasticity kinetics incorporates the Gilman model for dislocation multiplication and saturation. We discuss the application of this model to the simulation of experimental velocity interferometry data for experiments on Omega in which Fe was shock compressed to pressures beyond the {alpha}-to-{var_epsilon} phase transition pressure. The kinetics model is shown to fit the data reasonably well in this high strain rate regime and further allows quantification of the relative contributions of dislocation multiplication and drag. The sensitivity of the observed signatures to the kinetics model parameters is presented.

  7. Modeling anisotropic plasticity: Eulerian hydrocode applications of high strain-rate deformation processes

    Energy Technology Data Exchange (ETDEWEB)

    Clancy, S.P.; Burkett, M.W.; Maudlin, P.J.

    1997-05-01

    Previously developed constitutive models and solution algorithms for anisotropic elastoplastic material strength are implemented in the two-dimensional MESA hydrodynamics code. Quadratic yield functions fitted from polycrystal simulations for a metallic hexagonal-close-packed structure are utilized. An associative flow strength formulation incorporating these yield functions is solved using a geometric normal return method. A stretching rod problem is selected to investigate the effects of material anisotropy on a tensile plastic instability (necking). The rod necking rate and topology are compared for MESA simulations performed for both isotropic and anisotropic cases utilizing the Mechanical Threshold Stress flow stress model.

  8. Temperature increase of Zircaloy-4 cladding tubes due to plastic heat dissipation during tensile tests at 0.1-10 s-1 strain rates

    Science.gov (United States)

    Hellouin de Menibus, Arthur; Auzoux, Quentin; Besson, Jacques; Crépin, Jérôme

    2014-11-01

    This study is focused on the impact of rapid Reactivity Initiated Accident (RIA) representative strain rates (about 1 s-1 NEA, 2010) on the behavior and fracture of unirradiated cold work stress relieved Zircaloy-4 cladding tubes. Uniaxial ring tests (HT) and plane strain ring tensile tests (PST) were performed in the 0.1-10 s-1 strain rate range, at 25 °C. The local temperature increase due to plastic dissipation was measured with a high-speed infrared camera. Limited temperature increases were measured at 0.1 s-1 strain rate. Limited but not strongly localized temperature increases were measured at 1 s-1. Large temperature increase were measured at 5 and 10 s-1 (142 °C at 5 s-1 strain rate in HT tests). The local temperature increase induced heterogeneous temperature fields, which enhanced strain localization and resulted in a reduction of the plastic elongation at fracture.

  9. Computational Strain Gradient Crystal Plasticity

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Kysar, Jeffrey W.

    2011-01-01

    A model for strain gradient crystal visco-plasticity is formulated along the lines proposed by Fleck andWillis (2009) for isotropic plasticity. Size-effects are included in the model due to the addition of gradient terms in both the free energy as well as through a dissipation potential. A finite...... element solution method is presented, which delivers the slip-rate field and the velocity-field based on two minimum principles. Some plane deformation problems relevant for certain specific orientations of a face centered cubic crystal under plane loading conditions are studied, and effective in......-plane parameters are developed based on the crystallographic properties of the material. The problem of cyclic shear of a single crystal between rigid platens is studied as well as void growth of a cylindrical void....

  10. Plasticity induced by pre-existing defects during high strain-rate loading

    Science.gov (United States)

    Bringa, Eduardo

    2014-03-01

    High strain-rate deformation of metals has been typically studied for perfect monocrystals. Computational advances now allow more realistic simulations of materials including defects, which lower the Hugoniot Elastic Limit, and lead to microstructures differing from the ones from perfect monocrystals. As pre-existing defects one can consider vacancy clusters, dislocation loops, grain boundaries, etc. New analysis tools allow analysis of dislocation densities and twin fractions, for both f.c.c. and b.c.c. metals. Recent results for defective single crystal Ta [Tramontina et al.., High Energy Den. Phys. 10, 9 (2014), and Ruestes et al., Scripta Mat. 68, 818 (2013)], and for polycrystalline b.c.c metals [Tang et al., Mat. Sci. Eng. A 580, 414 (2013), and Gunkelmann et al., Phys. Rev. B 86, 144111 (2012)] will be highlighted, alongside new results for nanocrystalline Cu, Ta, Fe, and Zr [Ruestes et al., Scripta Mat. 71, 9 (2014)]. This work has been carried out in collaboration with D. Tramontina, C. Ruestes, E. Millan, J. Rodriguez-Nieva, M.A. Meyers, Y. Tang, H. Urbassek, N. Gunkelmann, A. Stukowski, M. Ruda, G. Bertolino, D. Farkas, A. Caro, J. Hawreliak, B. Remington, R. Rudd, P. Erhart, R. Ravelo, T. Germann, N. Park, M. Suggit, S. Michalik, A. Higginbotham and J. Wark. Funding by PICT2008-1325 and SeCTyP U.N. Cuyo.

  11. Computational strain gradient crystal plasticity

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Kysar, Jeffrey W.

    2014-01-01

    of plane crystal plasticity are studied: pure shear of a single crystal between rigid platens as well as plastic deformation around cylindrical voids in hexagonal close packed and face centered cubic crystals. Effective in-plane constitutive slip parameters for plane strain deformation of specifically...

  12. Dynamic response of Cu4Zr54 metallic glass to high strain rate shock loading: plasticity, spall and atomic-level structures

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Shengnian [Los Alamos National Laboratory; Arman, Bedri [Los Alamos National Laboratory; Germann, Timothy C [Los Alamos National Laboratory; Cagin, Tahir [TEXAS A& M UNIV

    2009-01-01

    We investigate dynamic response of Cu{sub 46}Zr{sub 54} metallic glass under adiabatic planar shock wave loading (one-dimensional strain) wjth molecular dynamics simulations, including Hugoniot (shock) states, shock-induced plasticity and spallation. The Hugoniot states are obtained up to 60 CPa along with the von Mises shear flow strengths, and the dynamic spall strength, at different strain rates and temperatures. The spall strengths likely represent the limiting values achievable in experiments such as laser ablation. For the steady shock states, a clear elastic-plastic transition is identified (e.g., in the shock velocity-particle velocity curve), and the shear strength shows strain-softening. However, the elastic-plastic transition across the shock front displays transient stress overshoot (hardening) above the Hugoniot elastic limit followed by a relatively sluggish relaxation to the steady shock state, and the plastic shock front steepens with increasing shock strength. The local von Mises shear strain analysis is used to characterize local deformation, and the Voronoi tessellation analysis, the corresponding short-range structures at various stages of shock, release, tension and spallation. The plasticity in this glass is manifested as localized shear transformation zones and of local structure rather than thermal origin, and void nucleation occurs preferentially at the highly shear-deformed regions. The Voronoi and shear strain analyses show that the atoms with different local structures are of different shear resistances that lead to shear localization (e.g., the atoms indexed with (0,0,12,0) are most shear-resistant, and those with (0,2,8,1) are highly prone to shear flow). The dynamic changes in local structures are consistent with the observed deformation dynamics.

  13. Distributions of energy storage rate and microstructural evolution in the area of plastic strain localization during uniaxial tension of austenitic steel

    Science.gov (United States)

    Oliferuk, W.; Maj, M.

    2015-08-01

    The presented work is devoted to an experimental determination of the energy storage rate in the area of strain localization. The experimental procedure involves two complementary techniques: i.e. infrared thermography (IRT) and visible light imaging. The results of experiments have shown that during the evolution of plastic strain localization the energy storage rate in some areas of the deformed specimen drops to zero. To interpret the decrease of the energy storage rate in terms of micro-mechanisms, microstructural observations using Transmission Electron Microscopy (TEM) and Electron Back Scattered Diffraction (EBSC) were performed. On the basis of microstructural studies it is believed that a 0 value of energy storage rate corresponds to the state in which only two dominant components of the texture appear, creating conditions for crystallographic shear banding.

  14. The role of microstructure in the modelling of plastic flow in P/M superalloys at forging temperatures and strain rate

    Science.gov (United States)

    Immarigeon, J. P.

    1984-09-01

    The application of computer aided plasticity analysis to model the deformation of alloys during forging with a view to optimizing the microstructure in forged components is presented. Finite element modelling techniques and a methodology for predicting local changes in grain size as a function of local deformation history predict the final grain sizes in the rim and the bore regions of a disc via process modelling and determines the processing conditions under which an optimum microstructure is produced. The effects of thermomechanical history on the evolution of microstructure in P/M superalloys under isothermal forging conditions and formulation of physically realistic constitutive relations for plastic flow which quantify the effects of the microstructural evolution, thereby allowing the prediction of final microstructure in forgings were studied. Using constant true strain rate uniaxial compression tests, microstructure flow property data were generated at isothermal foring temperatures and strain rates for a number of compacts. Deformation modelling for microstructural control is discussed. It is shown that the rate of change of grain size is an important parameter which governs changes in flow strength and is considered in the formulation of constitutive relations for compacts both in a coarse grained and in a fine grained superplastic condition. A deformation model for grain size and rate sensitive P/M superalloys and a methodology that can be applied to predict grain size distributions in forgings are presented.

  15. Strain gradient crystal plasticity effects on flow localization

    DEFF Research Database (Denmark)

    Borg, Ulrik

    2007-01-01

    In metal grains one of the most important failure mechanisms involves shear band localization. As the band width is small, the deformations are affected by material length scales. To study localization in single grains a rate-dependent crystal plasticity formulation for finite strains is presented...... in the absence of strain gradients. The model is used to study the effect of an internal material length scale on the localization of plastic flow in shear bands in a single crystal under plane strain tension. It is shown that the mesh sensitivity is removed when using the nonlocal material model considered...... for metals described by the reformulated Fleck-Hutchinson strain gradient plasticity theory. The theory is implemented numerically within a finite element framework using slip rate increments and displacement increments as state variables. The formulation reduces to the classical crystal plasticity theory...

  16. Using Omega and NIF to Advance Theories of High-Pressure, High-Strain-Rate Tantalum Plastic Flow

    Science.gov (United States)

    Rudd, R. E.; Arsenlis, A.; Barton, N. R.; Cavallo, R. M.; Huntington, C. M.; McNaney, J. M.; Orlikowski, D. A.; Park, H.-S.; Prisbrey, S. T.; Remington, B. A.; Wehrenberg, C. E.

    2015-11-01

    Precisely controlled plasmas are playing an important role as both pump and probe in experiments to understand the strength of solid metals at high energy density (HED) conditions. In concert with theory, these experiments have enabled a predictive capability to model material strength at Mbar pressures and high strain rates. Here we describe multiscale strength models developed for tantalum and vanadium starting with atomic bonding and extending up through the mobility of individual dislocations, the evolution of dislocation networks and so on up to full scale. High-energy laser platforms such as the NIF and the Omega laser probe ramp-compressed strength to 1-5 Mbar. The predictions of the multiscale model agree well with the 1 Mbar experiments without tuning. The combination of experiment and theory has shown that solid metals can behave significantly differently at HED conditions; for example, the familiar strengthening of metals as the grain size is reduced has been shown not to occur in the high pressure experiments. Work performed under the auspices of the U.S. Dept. of Energy by Lawrence Livermore National Lab under contract DE-AC52-07NA273.

  17. A new method to predict fatigue crack growth rate of materials based on average cyclic plasticity strain damage accumulation

    Institute of Scientific and Technical Information of China (English)

    Chen Long; Cai Lixun; Yao Di

    2013-01-01

    By introducing a fatigue blunting factor,the cyclic elasto-plastic Hutchinson-RiceRosengren (HRR) field near the crack tip under the cyclic loading is modified.And,an average damage per loading-cycle in the cyclic plastic deformation region is defined due to Manson-Coffin law.Then,according to the linear damage accumulation theory-Miner law,a new model for predicting the fatigue crack growth (FCG) of the opening mode crack based on the low cycle fatigue (LCF) damage is set up.The step length of crack propagation is assumed to be the size of cyclic plastic zone.It is clear that every parameter of the new model has clearly physical meaning which does not need any human debugging.Based on the LCF test data,the FCG predictions given by the new model are consistent with the FCG test results of Cr2Ni2MoV and X12CrMoWVNbN 10-1-1.What's more,referring to the relative researches,the good predictability of the new model is also proved on six kinds of materials.

  18. On the homogenization of metal matrix composites using strain gradient plasticity

    DEFF Research Database (Denmark)

    Azizi, Reza; Niordson, Christian Frithiof; Legarth, Brian Nyvang

    2014-01-01

    The homogenized response of metal matrix composites (MMC) is studied using strain gradient plasticity. The material model employed is a rate independent formulation of energetic strain gradient plasticity at the micro scale and conventional rate independent plasticity at the macro scale. Free...

  19. On lower order strain gradient plasticity theories

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Hutchinson, J. W.

    2003-01-01

    the tangent moduli governing increments of stress and strain. It is shown that the modification is far from benign from a mathematical standpoint, changing the qualitative character of solutions and leading to a new type of localization that is at odds with what is expected from a strain gradient theory......By way of numerical examples, this paper explores the nature of solutions to a class of strain gradient plasticity theories that employ conventional stresses, equilibrium equations and boundary conditions. Strain gradients come into play in these modified conventional theories only to alter....... The findings raise questions about the physical acceptability of this class of strain gradient theories....

  20. On lower order strain gradient plasticity theories

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Hutchinson, J. W.

    2002-01-01

    By way of numerical examples, this paper explores the nature of solutions to a class of strain gradient plasticity theories that employ conventional stresses, equilibrium equations and boundary conditions. Strain gradients come into play in these modified conventional theories only to alter the t...... the tangential moduli governing increments of stress and strain. It is shown that the modification is far from benign from a mathematical standpoint, changing the qualitative character of solutions and leading to a new type of localization that appears to be unphysical.......By way of numerical examples, this paper explores the nature of solutions to a class of strain gradient plasticity theories that employ conventional stresses, equilibrium equations and boundary conditions. Strain gradients come into play in these modified conventional theories only to alter...

  1. On fracture in finite strain gradient plasticity

    DEFF Research Database (Denmark)

    Martínez Pañeda, Emilio; Niordson, Christian Frithiof

    2016-01-01

    In this work a general framework for damage and fracture assessment including the effect of strain gradients is provided. Both mechanism-based and phenomenological strain gradient plasticity (SGP) theories are implemented numerically using finite deformation theory and crack tip fields are invest......In this work a general framework for damage and fracture assessment including the effect of strain gradients is provided. Both mechanism-based and phenomenological strain gradient plasticity (SGP) theories are implemented numerically using finite deformation theory and crack tip fields...... are investigated. Differences and similarities between the two approaches within continuum SGP modeling are highlighted and discussed. Local strain hardening promoted by geometrically necessary dislocations (GNDs) in the vicinity of the crack leads to much higher stresses, relative to classical plasticity...... predictions. These differences increase significantly when large strains are taken into account, as a consequence of the contribution of strain gradients to the work hardening of the material. The magnitude of stress elevation at the crack tip and the distance ahead of the crack where GNDs significantly alter...

  2. A mathematical basis for strain-gradient plasticity theory. Part II: Tensorial plastic multiplier

    Science.gov (United States)

    Fleck, N. A.; Willis, J. R.

    2009-07-01

    A phenomenological, flow theory version of gradient plasticity for isotropic and anisotropic solids is constructed along the lines of Gudmundson [Gudmundson, P., 2004. A unified treatment of strain-gradient plasticity. J. Mech. Phys. Solids 52, 1379-1406]. Both energetic and dissipative stresses are considered in order to develop a kinematic hardening theory, which in the absence of gradient terms reduces to conventional J 2 flow theory with kinematic hardening. The dissipative stress measures, work-conjugate to plastic strain and its gradient, satisfy a yield condition with associated plastic flow. The theory includes interfacial terms: elastic energy is stored and plastic work is dissipated at internal interfaces, and a yield surface is postulated for the work-conjugate stress quantities at the interface. Uniqueness and extremum principles are constructed for the solution of boundary value problems, for both the rate-dependent and the rate-independent cases. In the absence of strain gradient and interface effects, the minimum principles reduce to the classical extremum principles for a kinematically hardening elasto-plastic solid. A rigid-hardening version of the theory is also stated and the resulting theory gives rise to an extension to the classical limit load theorems. This has particular appeal as previous trial fields for limit load analysis can be used to generate immediately size-dependent bounds on limit loads.

  3. Constitutive modeling and computational implementation for finite strain plasticity

    Science.gov (United States)

    Reed, K. W.; Atluri, S. N.

    1985-01-01

    This paper describes a simple alternate approach to the difficult problem of modeling material behavior. Starting from a general representation for a rate-tpe constitutive equation, it is shown by example how sets of test data may be used to derive restrictions on the scalar functions appearing in the representation. It is not possible to determine these functions from experimental data, but the aforementioned restrictions serve as a guide in their eventual definition. The implications are examined for hypo-elastic, isotropically hardening plastic, and kinematically hardening plastic materials. A simple model for the evolution of the 'back-stress,' in a kinematic-hardening plasticity theory, that is entirely analogous to a hypoelastic stress-strain relation is postulated and examined in detail in modeling finitely plastic tension-torsion test. The implementation of rate-type material models in finite element algorithms is also discussed.

  4. Theory of Lattice Strain for Materials Undergoing Plastic Deformation

    Science.gov (United States)

    Karato, S.

    2008-12-01

    Radial x-ray diffraction is used to probe physical properties of materials including elastic and plastic properties. The theory used behind such an practice is the one developed by Singh (1993) in which the relation between lattice strain and elastic constants and macroscopic stress is derived. In this theory, the variation of inferred stress with the crystallographic planes, (hkl), is due to the elastic anisotropy. However, recent experimental studies showed that in many cases, the variation of stress with (hkl) far exceeds the value expected from this theory. I have developed a modified theory to rectify this problem with Singh's theory. In Singh's theory, the stress distribution in a polycrystalline material is treated only either unrelaxed or relaxed state. The role of plastic deformation is included only to the extent that plastic flow influences this stress state. Such an assumption corresponds to a Voigt model behavior, which is not an appropriate model at high temperatures where continuing plastic flow occurs with concurrent microscopic equilibrium, elastic deformation. This is a Maxwell model type behavior, and my model provides a stress analysis in a Maxwell material with anisotropic and non-linear power-law rheology. In this theory, the lattice strain corresponding to an imposed macroscopic strain-rate is calculated by three steps: (i) conversion of macroscopic strain-rate to macroscopic stress, (ii) conversion of macroscopic stress to microscopic stress at individual grains, and (iii) calculation of microscopic strain due to microscopic stress. The first step involves anisotropy in macroscopic viscosity that depends on anisotropy in crystal plasticity and lattice-preferred orientation. The second step involves anisotropic crystal plasticity and finally the third step involves elastic crystal anisotropy. In most cases, the influence of LPO is weak and in such a case, the lattice strain depends on (hkl) due to the anisotropy in both elastic and plastic

  5. A high-strain-rate superplastic ceramic.

    Science.gov (United States)

    Kim, B N; Hiraga, K; Morita, K; Sakka, Y

    2001-09-20

    High-strain-rate superplasticity describes the ability of a material to sustain large plastic deformation in tension at high strain rates of the order of 10-2 to 10-1 s-1 and is of great technological interest for the shape-forming of engineering materials. High-strain-rate superplasticity has been observed in aluminium-based and magnesium-based alloys. But for ceramic materials, superplastic deformation has been restricted to low strain rates of the order of 10-5 to 10-4 s-1 for most oxides and nitrides with the presence of intergranular cavities leading to premature failure. Here we show that a composite ceramic material consisting of tetragonal zirconium oxide, magnesium aluminate spinel and alpha-alumina phases exhibits superplasticity at strain rates up to 1 s-1. The composite also exhibits a large tensile elongation, exceeding 1,050 per cent for a strain rate of 0.4 s-1. The tensile flow behaviour and deformed microstructure of the material indicate that superplasticity is due to a combination of limited grain growth in the constitutive phases and the intervention of dislocation-induced plasticity in the zirconium oxide phase. We suggest that the present results hold promise for the application of shape-forming technologies to ceramic materials.

  6. Micromechanical modeling of damage in periodic composites using strain gradient plasticity

    DEFF Research Database (Denmark)

    Azizi, Reza

    2012-01-01

    Damage evolution at the fiber matrix interface in Metal Matrix Composites (MMCs) is studied using strain gradient theory of plasticity. The study includes the rate independent formulation of energetic strain gradient plasticity for the matrix, purely elastic model for the fiber and cohesive zone...... model under simple shear and transverse uniaxial tension using plane strain and periodic boundary conditions. The result of the overall response curve, effective plastic strain, effective stress and higher order stress distributions are shown. The effect of the material length scale, maximum stress...

  7. Strain y strain rate para dummies

    Directory of Open Access Journals (Sweden)

    Pastor Olaya, MD

    2011-11-01

    Full Text Available Desarrollos recientes en el campo de la ecocardiografía han permitido a los cardiólogos cuantificar de manera objetiva la función miocárdica regional y global con base en los conceptos de deformación (strain y velocidad de deformación (strain rate que pueden calcularse de manera no invasiva tanto en el ventrículo izquierdo como en el derecho, y suministrar valiosa información en múltiples escenarios clínicos. Dado que esta técnica novedosa y promisoria se utiliza cada vez más en la clínica y en estudios de investigación, se hace necesario el conocimiento adecuado de sus principios, así como de sus aspectos técnicos, alcances y limitaciones para una mejor implementación. En este artículo se busca dar explicación a los conceptos fundamentales y las potenciales aplicaciones clínicas de la strain y la strain rate derivados por speckle tracking (strain 2D.

  8. Strain gradient plasticity effects in whisker-reinforced metals

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof

    2002-01-01

    A metal reinforced by fibers in the micron range is studied using the strain gradient plasticity theory of Fleck and Hutchinson (2001). Cell-model analyzes are used to study the influence of the material length parameters numerically. Different higher order boundary conditions are considered...... at the fiber-matrix interface. The results are presented as overall stress-strain curves for the whisker-reinforced metal, and also contour plots of effective plastic strain are shown. The strain gradient plasticity theory predicts a significant stiffening effect when compared to conventional models...

  9. An incremental flow theory for crystal plasticity incorporating strain gradient effects

    DEFF Research Database (Denmark)

    Nellemann, Christopher; Niordson, Christian Frithiof; Nielsen, Kim Lau

    2017-01-01

    The present work investigates a new approach to formulating a rate-independent strain gradient theory for crystal plasticity. The approach takes as offset recent discussions published in the literature for isotropic plasticity, and a key ingredient of the present work is the manner in which a gra...

  10. Strain hardening of polymer glasses: Entanglements, energetics, and plasticity

    Science.gov (United States)

    Hoy, Robert S.; Robbins, Mark O.

    2008-03-01

    Simulations are used to examine the microscopic origins of strain hardening in polymer glasses. While stress-strain curves for a wide range of temperature can be fit to the functional form predicted by entropic network models, many other results are fundamentally inconsistent with the physical picture underlying these models. Stresses are too large to be entropic and have the wrong trend with temperature. The most dramatic hardening at large strains reflects increases in energy as chains are pulled taut between entanglements rather than a change in entropy. A weak entropic stress is only observed in shape recovery of deformed samples when heated above the glass transition. While short chains do not form an entangled network, they exhibit partial shape recovery, orientation, and strain hardening. Stresses for all chain lengths collapse when plotted against a microscopic measure of chain stretching rather than the macroscopic stretch. The thermal contribution to the stress is directly proportional to the rate of plasticity as measured by breaking and reforming of interchain bonds. These observations suggest that the correct microscopic theory of strain hardening should be based on glassy state physics rather than rubber elasticity.

  11. Equivalent Plastic Strain Gradient Plasticity with Grain Boundary Hardening and Comparison to Discrete Dislocation Dynamics

    CERN Document Server

    Bayerschen, E; Wulfinghoff, S; Weygand, D; Böhlke, T

    2015-01-01

    The gradient crystal plasticity framework of Wulfinghoff et al. [53] incorporating an equivalent plastic strain and grain boundary yielding, is extended with additional grain boundary hardening. By comparison to averaged results from many discrete dislocation dynamics (DDD) simulations of an aluminum type tricrystal under tensile loading, the new hardening parameter in the continuum model is calibrated. It is shown that although the grain boundaries (GBs) in the discrete simulations are impenetrable, an infinite GB yield strength corresponding to microhard GB conditions, is not applicable in the continuum model. A combination of a finite GB yield strength with an isotropic bulk Voce hardening relation alone also fails to model the plastic strain profiles obtained by DDD. Instead, a finite GB yield strength in combination with GB hardening depending on the equivalent plastic strain at the GBs is shown to give a better agreement to DDD results. The differences in the plastic strain profiles obtained in DDD simu...

  12. Strain y strain rate para dummies Strain and strain rate for dummies

    Directory of Open Access Journals (Sweden)

    Pastor Olaya

    2011-12-01

    Full Text Available Desarrollos recientes en el campo de la ecocardiografía han permitido a los cardiólogos cuantificar de manera objetiva la función miocárdica regional y global con base en los conceptos de deformación (strain y velocidad de deformación (strain rate que pueden calcularse de manera no invasiva tanto en el ventrículo izquierdo como en el derecho, y suministrar valiosa información en múltiples escenarios clínicos. Dado que esta técnica novedosa y promisoria se utiliza cada vez más en la clínica y en estudios de investigación, se hace necesario el conocimiento adecuado de sus principios, así como de sus aspectos técnicos, alcances y limitaciones para una mejor implementación. En este artículo se busca dar explicación a los conceptos fundamentales y las potenciales aplicaciones clínicas de la strain y la strain rate derivados por speckle tracking (strain 2D.Recent developments in the field of echocardiography have allowed cardiologists to objectively quantify regional and global myocardial function based on the deformation (strain and strain rate which can be calculated non-invasively in both the left or right ventricle, and provide valuable information in multiple clinical settings. Since this new technique is promising and is being increasingly used in clinical and research studies, the adequate knowledge of its principles and its technical aspects, scope and limitations are necessary for its better implementation. This article seeks to explain fundamental concepts and potential clinical applications of strain and strain rate derived by speckle tracking (2D strain.

  13. Single crystal plasticity by modeling dislocation density rate behavior

    Energy Technology Data Exchange (ETDEWEB)

    Hansen, Benjamin L [Los Alamos National Laboratory; Bronkhorst, Curt [Los Alamos National Laboratory; Beyerlein, Irene [Los Alamos National Laboratory; Cerreta, E. K. [Los Alamos National Laboratory; Dennis-Koller, Darcie [Los Alamos National Laboratory

    2010-12-23

    The goal of this work is to formulate a constitutive model for the deformation of metals over a wide range of strain rates. Damage and failure of materials frequently occurs at a variety of deformation rates within the same sample. The present state of the art in single crystal constitutive models relies on thermally-activated models which are believed to become less reliable for problems exceeding strain rates of 10{sup 4} s{sup -1}. This talk presents work in which we extend the applicability of the single crystal model to the strain rate region where dislocation drag is believed to dominate. The elastic model includes effects from volumetric change and pressure sensitive moduli. The plastic model transitions from the low-rate thermally-activated regime to the high-rate drag dominated regime. The direct use of dislocation density as a state parameter gives a measurable physical mechanism to strain hardening. Dislocation densities are separated according to type and given a systematic set of interactions rates adaptable by type. The form of the constitutive model is motivated by previously published dislocation dynamics work which articulated important behaviors unique to high-rate response in fcc systems. The proposed material model incorporates thermal coupling. The hardening model tracks the varying dislocation population with respect to each slip plane and computes the slip resistance based on those values. Comparisons can be made between the responses of single crystals and polycrystals at a variety of strain rates. The material model is fit to copper.

  14. Estimating the plastic strain with the use of acoustic anisotropy

    Science.gov (United States)

    Belyaev, A. K.; Lobachev, A. M.; Modestov, V. S.; Pivkov, A. V.; Polyanskii, V. A.; Semenov, A. S.; Tret'yakov, D. A.; Shtukin, L. V.

    2016-09-01

    Experimental verification is used to show that reference specimens and structure unloading do not permit obtaining an adequate estimate of plastic strain by measuring the acoustic anisotropy. Analytic estimates of the speed of propagation of a plane acoustic wave of various polarizations in an elastoplastic material in the direction orthogonal to the action of preliminary uniaxial stress are obtained. An analysis of the obtained relations reveala an advantage of using absolute values of the velocity of longitudinal and transverse waves for the plastic strain identification. In contrast to acoustic anisotropy, the velocities vary monotonically in a wider range of plastic strains. At the same time, the elastic strain does not affect the longitude wave velocity, which allows one to use the measurement results to estimate the character of strains.

  15. A strain gradient plasticity theory with application to wire torsion

    KAUST Repository

    Liu, J. X.

    2014-06-05

    Based on the framework of the existing strain gradient plasticity theories, we have examined three kinds of relations for the plastic strain dependence of the material intrinsic length scale, and thus developed updated strain gradient plasticity versions with deformation-dependent characteristic length scales. Wire torsion test is taken as an example to assess existing and newly built constitutive equations. For torsion tests, with increasing plastic strain, a constant intrinsic length predicts too high a torque, while a decreasing intrinsic length scale can produce better predictions instead of the increasing one, different from some published observations. If the Taylor dislocation rule is written in the Nix-Gao form, the derived constitutive equations become singular when the hardening exponent gets close to zero, which seems questionable and calls for further experimental clarifications on the exact coupling of hardening due to statistically stored dislocations and geometrically necessary dislocations. Particularly, when comparing the present model with the mechanism-based strain gradient plasticity, the present model satisfies the reciprocity relation naturally and gives different predictions even under the same parameter setting. © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

  16. Strain gradient crystal plasticity: A continuum mechanics approach to modeling micro-structural evolution

    DEFF Research Database (Denmark)

    El-Naaman, Salim Abdallah; Nielsen, Kim Lau; Niordson, Christian Frithiof

    2015-01-01

    In agreement with dislocation theory, recent experiments show, both quantitatively and qualitatively, how geometrically necessary dislocations (GNDs) distribute in dislocation wall and cell structures. Hence, GND density fields are highly localized with large gradients and discontinuities occurring...... between the cells. This behavior is not typical for strain gradient crystal plasticity models. The present study employs a higher order extension of conventional crystal plasticity theory in which the viscous slip rate is influenced by the gradients of GND densities through a back stress...

  17. Strain gradient crystal plasticity: A continuum mechanics approach to modeling micro-structural evolution

    DEFF Research Database (Denmark)

    El-Naaman, Salim Abdallah; Nielsen, Kim Lau; Niordson, Christian Frithiof

    2015-01-01

    In agreement with dislocation theory, recent experiments show, both quantitatively and qualitatively, how geometrically necessary dislocations (GNDs) distribute in dislocation wall and cell structures. Hence, GND density fields are highly localized with large gradients and discontinuities occurring...... between the cells. This behavior is not typical for strain gradient crystal plasticity models. The present study employs a higher order extension of conventional crystal plasticity theory in which the viscous slip rate is influenced by the gradients of GND densities through a back stress...

  18. Generalizing J2 flow theory: Fundamental issues in strain gradient plasticity

    Institute of Scientific and Technical Information of China (English)

    John W. Hutchinson

    2012-01-01

    It has not been a simple matter to obtain a sound extension of the classical J2 flow theory of plasticity that incorporates a dependence on plastic strain gradients and that is capable of capturing size-dependent behaviour of metals at the micron scale.Two classes of basic extensions of classical J2 theory have been proposed:one with increments in higher order stresses related to increments of strain gradients and the other characterized by the higher order stresses themselves expressed in terms of increments of strain gradients. The theories proposed by Muhlhaus and Aifantis in 1991 and Fleck and Hutchinson in 2001 are in the first class,and,as formulated,these do not always satisfy thermodynamic requirements on plastic dissipation.On the other hand,theories of the second class proposed by Gudmundson in 2004 and Gurtin and Anand in 2009 have the physical deficiency that the higher order stress quantities can change discontinuously for bodies subject to arbitrarily small load changes.The present paper lays out this background to the quest for a sound phenomenological extension of the rateindependent J2 flow theory of plasticity to include a dependence on gradients of plastic strain.A modification of the Fleck-Hutchinson formulation that ensures its thermo dynamic integrity is presented and contrasted with a comparable formulation of the second class where in the higher order stresses are expressed in terms of the plastic strain rate.Both versions are constructed to reduce to the classical J2 flow theory of plasticity when the gradients can be neglected and to coincide with the simpler and more readily formulated J2 deformation theory of gradient plasticity for deformation histories characterized by proportional straining.

  19. Fracture of anisotropic materials with plastic strain-gradient effects

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang

    2013-01-01

    parameter is adopted. The fracture process along the fiber-matrix interface is modeled using a recently proposed cohesive law extension having an additional material length parameter. Due to the fiber-matrix fracture a sudden stress-drop is seen in the macroscopic stress-strain response which defines......A unit cell is adopted to numerically analyze the effect of plastic anisotropy on frac-ture evolution in a micro-reinforced fiber-composite. The matrix material exhibit size-effects and an anisotropic strain-gradient plasticity model accounting for such size-effects through a mate-rial length scale...... the failure strain of the composite. The effect of the two material length parameters on the failure strain of the composite is studied. For small values of the material length scale parameter conventional predictions are obtained. Larger values of the material length scale parameter result in corresponding...

  20. Strain gradient plasticity analysis of elasto-plastic contact between rough surfaces

    Science.gov (United States)

    Song, H.; Van der Giessen, E.; Liu, X.

    2016-11-01

    From a microscopic point of view, the real contact area between two rough surfaces is the sum of the areas of contact between facing asperities. Since the real contact area is a fraction of the nominal contact area, the real contact pressure is much higher than the nominal contact pressure, which results in plastic deformation of asperities. As plasticity is size dependent at size scales below tens of micrometers, with the general trend of smaller being harder, macroscopic plasticity is not suitable to describe plastic deformation of small asperities and thus fails to capture the real contact area and pressure accurately. Here we adopt conventional mechanism-based strain gradient plasticity (CMSGP) to analyze the contact between a rigid platen and an elasto-plastic solid with a rough surface. Flattening of a single sinusoidal asperity is analyzed first to highlight the difference between CMSGP and J2 isotropic plasticity. For the rough surface contact, besides CMSGP, pure elastic and J2 isotropic plasticity analysis is also carried out for comparison. In all cases, the contact area A rises linearly with the applied load, but with a different slope which implies that the mean contact pressures are different. CMSGP produces qualitative changes in the distributions of local contact pressures compared with pure elastic and J2 isotropic plasticity analysis, furthermore, bounded by the two.

  1. Stress-strain response of plastic waste mixed soil.

    Science.gov (United States)

    Babu, G L Sivakumar; Chouksey, Sandeep Kumar

    2011-03-01

    Recycling plastic waste from water bottles has become one of the major challenges worldwide. The present study provides an approach for the use plastic waste as reinforcement material in soil. The experimental results in the form of stress-strain-pore water pressure response are presented. Based on experimental test results, it is observed that the strength of soil is improved and compressibility reduced significantly with addition of a small percentage of plastic waste to the soil. The use of the improvement in strength and compressibility response due to inclusion of plastic waste can be advantageously used in bearing capacity improvement and settlement reduction in the design of shallow foundations. Copyright © 2010 Elsevier Ltd. All rights reserved.

  2. A numerical method for determining the strain rate intensity factor under plane strain conditions

    Science.gov (United States)

    Alexandrov, S.; Kuo, C.-Y.; Jeng, Y.-R.

    2016-07-01

    Using the classical model of rigid perfectly plastic solids, the strain rate intensity factor has been previously introduced as the coefficient of the leading singular term in a series expansion of the equivalent strain rate in the vicinity of maximum friction surfaces. Since then, many strain rate intensity factors have been determined by means of analytical and semi-analytical solutions. However, no attempt has been made to develop a numerical method for calculating the strain rate intensity factor. This paper presents such a method for planar flow. The method is based on the theory of characteristics. First, the strain rate intensity factor is derived in characteristic coordinates. Then, a standard numerical slip-line technique is supplemented with a procedure to calculate the strain rate intensity factor. The distribution of the strain rate intensity factor along the friction surface in compression of a layer between two parallel plates is determined. A high accuracy of this numerical solution for the strain rate intensity factor is confirmed by comparison with an analytic solution. It is shown that the distribution of the strain rate intensity factor is in general discontinuous.

  3. Limit analysis of viscoplastic thick-walled cylinder and spherical shell under internal pressure using a strain gradient plasticity theory

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Plastic limit load of viscoplastic thick-walled cylinder and spherical shell subjected to internal pressure is investigated analytically using a strain gradient plastic-itv theory. As a result, the current solutions can capture the size effect at the micron scale. Numerical results show that the smaller the inner radius of the cylinder or spherical shell, the more significant the scale effects. Results also show that the size effect is more evident with increasing strain or strain-rate sensitivity index. The classical plastic-based solutions of the same problems are shown to be a special case of the present solution.

  4. Strain gradient plasticity effects in whisker-reinforced metals

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof

    2003-01-01

    A metal reinforced by fibers in the micron range is studied using the strain gradient plasticity theory of Fleck and Hutchinson (J. Mech. Phys. Solids 49 (2001) 2245). Cell-model analyses are used to study the influence of the material length parameters numerically, for both a single parameter...... version and the multiparameter theory, and significant differences between the predictions of the two models are reported. It is shown that modeling fiber elasticity is important when using the present theories. A significant stiffening effect when compared to conventional models is predicted, which...... is a result of a significant decrease in the level of plastic strain. Moreover, it is shown that the relative stiffening effect increases with fiber volume fraction. The higher-order nature of the theories allows for different higher-order boundary conditions at the fiber-matrix interface, and these boundary...

  5. Multiplicative earthquake likelihood models incorporating strain rates

    Science.gov (United States)

    Rhoades, D. A.; Christophersen, A.; Gerstenberger, M. C.

    2017-01-01

    SUMMARYWe examine the potential for strain-rate variables to improve long-term earthquake likelihood models. We derive a set of multiplicative hybrid earthquake likelihood models in which cell rates in a spatially uniform baseline model are scaled using combinations of covariates derived from earthquake catalogue data, fault data, and strain-rates for the New Zealand region. Three components of the strain rate estimated from GPS data over the period 1991-2011 are considered: the shear, rotational and dilatational strain rates. The hybrid model parameters are optimised for earthquakes of M 5 and greater over the period 1987-2006 and tested on earthquakes from the period 2012-2015, which is independent of the strain rate estimates. The shear strain rate is overall the most informative individual covariate, as indicated by Molchan error diagrams as well as multiplicative modelling. Most models including strain rates are significantly more informative than the best models excluding strain rates in both the fitting and testing period. A hybrid that combines the shear and dilatational strain rates with a smoothed seismicity covariate is the most informative model in the fitting period, and a simpler model without the dilatational strain rate is the most informative in the testing period. These results have implications for probabilistic seismic hazard analysis and can be used to improve the background model component of medium-term and short-term earthquake forecasting models.

  6. The genetics of phenotypic plasticity. XI. Joint evolution of plasticity and dispersal rate.

    Science.gov (United States)

    Scheiner, Samuel M; Barfield, Michael; Holt, Robert D

    2012-08-01

    In a spatially heterogeneous environment, the rate at which individuals move among habitats affects whether selection favors phenotypic plasticity or genetic differentiation, with high dispersal rates favoring trait plasticity. Until now, in theoretical explorations of plasticity evolution, dispersal rate has been treated as a fixed, albeit probabilistic, characteristic of a population, raising the question of what happens when the propensity to disperse and trait plasticity are allowed to evolve jointly. We examined the effects of their joint evolution on selection for plasticity using an individual-based computer simulation model. In the model, the environment consisted of a linear gradient of 50 demes with dispersal occurring either before or after selection. Individuals consisted of loci whose phenotypic expression either are affected by the environment (plastic) or are not affected (nonplastic), plus a locus determining the propensity to disperse. When dispersal rate and trait plasticity evolve jointly, the system tends to dichotomous outcomes of either high trait plasticity and high dispersal, or low trait plasticity and low dispersal. The outcome strongly depended on starting conditions, with high trait plasticity and dispersal favored when the system started at high values for either trait plasticity or dispersal rate (or both). Adding a cost of plasticity tended to drive the system to genetic differentiation, although this effect also depended on initial conditions. Genetic linkage between trait plasticity loci and dispersal loci further enhanced this strong dichotomy in evolutionary outcomes. All of these effects depended on organismal life history pattern, and in particular whether selection occurred before or after dispersal. These results can explain why adaptive trait plasticity is less common than might be expected.

  7. Constitutive Relation of Yunjialing Anthracite Under Medium Strain Rate

    Institute of Scientific and Technical Information of China (English)

    GAO Wen-jiao; SHAN Ren-liang; WANG Gong-cheng; CHENG Rui-qiang

    2007-01-01

    By means of the split Hopkinson pressure bar (SHPB) testing system, this paper presents a dynamic constitutive relation of anthracite at a strain rate of ε =5-85s-1. Generally, the dynamic stress-strain curve for this kind of anthracite under uni-axial compression has the following four stages: a non-linear loading stage, a plastic yielding stage, a strain-strengthening stage and an unloading breakage stage. Correspondingly, the initial elastic modulus Eb, the yielding strength σs and the ultimate strength σb increase along with an increasing strain rate. The time-dependent elasticity was identified when we analyzed the mechanical properties of anthracite. Based on characteristics of measured dynamic stress-strain curves and an analysis of existing rock dynamic constitutive models, as well as a preparatory simulation, a new visco-elastic damage model has been introduced in this paper. A linear spring is put parallel to two Maxwell units with different relaxation times to express two distinct plastic flows. The damage D is equal to [Eb- E(εi)]/Eb, where Eb is the beginning modulus and the E(εi) is the slope of a connected line between the origin point and any other point on a tested stress-strain curve. In the new constitutive model, one Maxwell unit with low relaxation time (ψ)1 is used to describe the response of anthracite to a low strain rate, while the other, with a high relaxation time (ψ)2 describes the response of anthracite to a high strain rate. Simulated stress-strain curves from the new model are consistent with the measured curves.

  8. Strain gradient effects on steady state crack growth in rate-sensitive materials

    DEFF Research Database (Denmark)

    Nielsen, Kim Lau; Niordson, Christian Frithiof; Hutchinson, John W.

    2012-01-01

    Steady state crack propagation produce substantial plastic strain gradients near the tip, which are accompanied by a high density of geometrically necessary dislocations and additional local strain hardening. Here, the objective is to study these gradient effects on Mode I toughness...... of a homogeneous rate-sensitive metal, using a higher order plasticity theory. Throughout, emphasis is on the toughness rate-sensitivity, as a recent numerical study of a conventional material (no gradient effects) has indicated a significant influence of both strain rate hardening and crack tip velocity. Moreover......, a characteristic velocity, at which the toughness becomes independent of the rate-sensitivity, has been observed. It is the aim to bring forward a similar characteristic velocity for the current strain gradient visco-plastic model, as-well as to signify its use in future visco-plastic material modeling....

  9. Creep Strain and Strain Rate Response of 2219 Al Alloy at High Stress Levels

    Science.gov (United States)

    Taminger, Karen M. B.; Wagner, John A.; Lisagor, W. Barry

    1998-01-01

    As a result of high localized plastic deformation experienced during proof testing in an International Space Station connecting module, a study was undertaken to determine the deformation response of a 2219-T851 roll forging. After prestraining 2219-T851 Al specimens to simulate strains observed during the proof testing, creep tests were conducted in the temperature range from ambient temperature to 107 C (225 F) at stress levels approaching the ultimate tensile strength of 2219-T851 Al. Strain-time histories and strain rate responses were examined. The strain rate response was extremely high initially, but decayed rapidly, spanning as much as five orders of magnitude during primary creep. Select specimens were subjected to incremental step loading and exhibited initial creep rates of similar magnitude for each load step. Although the creep rates decreased quickly at all loads, the creep rates dropped faster and reached lower strain rate levels for lower applied loads. The initial creep rate and creep rate decay associated with primary creep were similar for specimens with and without prestrain; however, prestraining (strain hardening) the specimens, as in the aforementioned proof test, resulted in significantly longer creep life.

  10. Determination of dynamic fracture initiation toughness of elastic-plastic materials at intermediate strain rates; Obtencion de la tenacidad de fractura dinamica de iniciacion de materiales elastolasticos a velocidad de deformacion intermedias

    Energy Technology Data Exchange (ETDEWEB)

    Fernandez-Saez, J.; Luna de, S.; Rubio, L.; Perez-Castellanos, J. L.; Navarro, C.

    2001-07-01

    An earlier paper dealt with the experimental techniques used to determine the dynamic fracture properties of linear elastic materials. Here we describe those most commonly used as elastoplastic materials, limiting the study to the initiation fracture toughness at the intermediate strain rate (of around 10''2 s''-1). In this case the inertial forces are negligible and it is possible to apply the static solutions. With this stipulation, the analysis can be based on the methods of testing in static conditions. The dynamic case differs basically, from the static one, in the influence of the strain rate on the properties of the material. (Author) 57 refs.

  11. Relationship between burgers vectors of dislocations and plastic strain localization patterns in compression-strained alkali halide crystals

    Science.gov (United States)

    Barannikova, S. A.; Nadezhkin, M. V.; Zuev, L. B.

    2011-08-01

    Plastic strain localization patterns in compression-strained alkali halide (NaCl, KCl, and LiF) crystals have been studied using a double-exposure speckle photography technique. The main parameters of strain localization autowaves at the linear stages of deformation hardening in alkali halide crystals have been determined. A quantitative relationship between the macroscopic parameters of plastic flow localization and microscopic parameters of strained alkali halide crystals has been established.

  12. Plasticity of Cu nanoparticles: Dislocation-dendrite-induced strain hardening and a limit for displacive plasticity

    Directory of Open Access Journals (Sweden)

    Antti Tolvanen

    2013-03-01

    Full Text Available The plastic behaviour of individual Cu crystallites under nanoextrusion is studied by molecular dynamics simulations. Single-crystal Cu fcc nanoparticles are embedded in a spherical force field mimicking the effect of a contracting carbon shell, inducing pressure on the system in the range of gigapascals. The material is extruded from a hole of 1.1–1.6 nm radius under athermal conditions. Simultaneous nucleation of partial dislocations at the extrusion orifice leads to the formation of dislocation dendrites in the particle causing strain hardening and high flow stress of the material. As the extrusion orifice radius is reduced below 1.3 Å we observe a transition from displacive plasticity to solid-state amorphisation.

  13. Effect of the cooling rate on plastic deformability of a Zr-based bulk metallic glass

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The present work found the plastic deformability of Zr65Cu17.5Ni10Al7.5 BMG dependent on the cooling rate during the formation from the molten state alloy. The deformation behavior in the compression test of φ 2 mm Zr65Cu17.5Ni10Al7.5 BMGs as-cast or lathed from different sizes as-cast samples was characterized, and they exhibited different plastic strains. The compressive plastic strain increases with the decreasing diameter of the as-cast specimens, i.e. with increasing the cooling rate. It is suggested that free volume content in the BMGs, which is related to the cooling rate during the rapid solidification, could play an important role in the deformation process of the BMGs.

  14. A Theory of Rate-Dependent Plasticity

    Science.gov (United States)

    1984-05-01

    impact conditions, where a considerable amount of plastic work is liberated as heat, this athermal assumption becomes increasingly poor for defining...crystal microplasticity use a variety of parameters, such as mobile dislocation density and velocity, all of which are eventually related in some manner... impact problems and are not generally encountered in structural integrity analyses. Some final observations concerning tests of material at constant

  15. Strain gradient plasticity-based modeling of hydrogen environment assisted cracking

    DEFF Research Database (Denmark)

    Martínez Pañeda, Emilio; Niordson, Christian Frithiof; P. Gangloff, Richard

    2016-01-01

    Finite element analysis of stress about a blunt crack tip, emphasizing finite strain and phenomenologicaland mechanism-based strain gradient plasticity (SGP) formulations, is integrated with electrochemical assessment of occluded-crack tip hydrogen (H) solubility and two H-decohesion models......; it is imperative to account for SGP in H cracking models. Predictions of the threshold stress intensity factor and H-diffusion limited Stage II crack growth rate agree with experimental data for a high strength austenitic Ni-Cusuperalloy (Monel®K-500) and two modern ultra-high strength martensitic steels (Aer...

  16. Strain rate effects in stress corrosion cracking

    Energy Technology Data Exchange (ETDEWEB)

    Parkins, R.N. (Newcastle upon Tyne Univ. (UK). Dept. of Metallurgy and Engineering Materials)

    1990-03-01

    Slow strain rate testing (SSRT) was initially developed as a rapid, ad hoc laboratory method for assessing the propensity for metals an environments to promote stress corrosion cracking. It is now clear, however, that there are good theoretical reasons why strain rate, as opposed to stress per se, will often be the controlling parameter in determining whether or not cracks are nucleated and, if so, are propagated. The synergistic effects of the time dependence of corrosion-related reactions and microplastic strain provide the basis for mechanistic understanding of stress corrosion cracking in high-pressure pipelines and other structures. However, while this may be readily comprehended in the context of laboratory slow strain tests, its extension to service situations may be less apparent. Laboratory work involving realistic stressing conditions, including low-frequency cyclic loading, shows that strain or creep rates give good correlation with thresholds for cracking and with crack growth kinetics.

  17. Some Misunderstandings on Rotation of Crystals and Reasonable Plastic Strain Rate%关于晶体旋转的误解及合理塑性应变速度

    Institute of Scientific and Technical Information of China (English)

    赵祖武

    2001-01-01

    It is pointed out that crystals are disc rete but not continuous materials. Hence the rotation R in decom position F=RU and spin W in F-1 are not correct. Errors will arise in plastic defo rmation rate if it is directly expressed with amounts of velocity of slips in g lide systems such as vn. The geo metrical figure of crystal lattices does not change after slips and based on thi s idea a simple way in mechanics of continuous media to get the plastic deformat ions rate induced by slips is proposed. Constitutive equations are recommended%指出晶体是离散的而不是连续的材料,因此在极 分解F=RU中的旋转R及F-1中的旋率W不是正确的塑性变形速度若直接以滑移系中的滑移速度来表示,如νn,则差错将会产生滑移后的晶格几何形状并不改变,基于此概念提出了连续介质力学范围内的一个简单途径来表达滑移产生的塑性应变速度建议了大变形下的本构方程

  18. Discussion and calculation on welding residual longitudinal stress and plastic strain by finite element method

    Institute of Scientific and Technical Information of China (English)

    Hong-yuan FANG; Xue-qiu ZHANG; Jian-guo WANG; Xue-song LIU; Shen QU

    2009-01-01

    In recent years, some researchers have put forward the new viewpoint that the weld is merely formed during the cooling process, not concerned with the heating process. According to this view, it can be concluded that it is not the compressive but the tensile plastic strain that may remain in the weld. To analyze the formation mechanism of the longitudinal residual stress and plastic strain, finite element method (FEM) is employed in this paper to model the welding longitudinal residual stress and plastic strain. The calculation results show that both the residual compressive plastic strain and the tensile stress in the longitudinal direction can be found in the weld.

  19. Strain rate effects on GRP, KRP and CFRP composite laminates

    Energy Technology Data Exchange (ETDEWEB)

    Al-Hassani, S.T.S.; Kaddour, A.S. [University of Manchester Inst. of Science and Technology (UMIST) (United Kingdom). Dept. of Mechanical Engineering

    1998-05-01

    This paper first reviews published research work on the effect of strain-rate on the in-plane mechanical properties of continuous Kevlar (KRP), glass (GRP) and carbon (CFRP) fibre reinforced plastic materials. A detailed description of techniques employed for testing composite materials at a wide range of strain rates is given. Recent relevant test results are presented showing the variation of mechanical properties with strain rates for unidirectional and multidirectional laminates under in-plane loading. The paper then concentrates on current activities on indirect determination of unidirectional dynamic properties from the behaviour of angle ply laminates by means of an extraction process. Theoretical procedures for extracting the longitudinal, transverse and in-plane shear properties are outlined. An extension to those procedures allowing simultaneous determination of transverse and in-plane shear moduli of a ply is introduced and results using this method are presented for KRP and CFRP under combined strain rate and temperature. Existing theories and mechanisms describing the combined effects of the temperature and the strain-rate on the mechanical response of composite materials are outlined. (orig.) 98 refs.

  20. ON PLASTIC ANISOTROPY OF CONSTITUTIVE MODEL FOR RATE-DEPENDENT SINGLE CRYSTAL

    Institute of Scientific and Technical Information of China (English)

    张光; 张克实; 冯露

    2005-01-01

    An algorithm for single crystals was developed and implemented to simulate plastic anisotropy using a rate-dependent slip model. The proposed procedure was a slightly modified form of single crystal constitutive model of Sarma and Zacharia. Modified Euler method, together with Newton-Raphson method was used to integrate this equation which was stable and efficient. The model together with the developed algorithm was used to study three problems. First, plastic anisotropy was examined by simulating the crystal deformation in tension and plane strain compression, respectively. Secondly, the orientation effect of some material parameters in the model and applied strain rate on plastic anisotropy for single crystal also is investigated. Thirdly, the influence of loading direction on the active slip system was discussed.

  1. Multi-scale modeling of the impact response of a strain-rate sensitive high-manganese austenitic steel

    OpenAIRE

    Canadinç, Demircan; Önal, Orkun; Özmenci, Cemre

    2014-01-01

    A multi-scale modeling approach was applied to predict the impact response of a strain rate sensitive high-manganese austenitic steel. The roles of texture, geometry, and strain rate sensitivity were successfully taken into account all at once by coupling crystal plasticity and finite element (FE) analysis. Specifically, crystal plasticity was utilized to obtain the multi-axial flow rule at different strain rates based on the experimental deformation response under uniaxial ten...

  2. A new macroscopically anisotropic pressure dependent yield function for metal matrix composite based on strain gradient plasticity for the microstructure

    DEFF Research Database (Denmark)

    Azizi, Reza; Legarth, Brian Nyvang; Niordson, Christian Frithiof

    2013-01-01

    Metal matrix composites with long aligned elastic fibers are studied using an energetic rate independent strain gradient plasticity theory with an isotropic pressure independent yield function at the microscale. The material response is homogenized to obtain a conventional macroscopic model...... that exhibits anisotropic yield properties with a pressure dependence. At the microscale free energy includes both elastic strains and plastic strain gradients, and the theory demands higher order boundary conditions in terms of plastic strain or work conjugate higher order tractions. The mechanical response...... of the composite is inclined compared to a standard pressure independent yield surfaces. The evolution of the macroscopic yield surface is investigated by quantifying both anisotropic hardening (expansion) and kinematic hardening (translation), where the coefficients of anisotropy and the Bauschinger stress...

  3. Using strain rates to forecast seismic hazards

    Science.gov (United States)

    Evans, Eileen

    2017-01-01

    One essential component in forecasting seismic hazards is observing the gradual accumulation of tectonic strain accumulation along faults before this strain is suddenly released as earthquakes. Typically, seismic hazard models are based on geologic estimates of slip rates along faults and historical records of seismic activity, neither of which records actively accumulating strain. But this strain can be estimated by geodesy: the precise measurement of tiny position changes of Earth’s surface, obtained from GPS, interferometric synthetic aperture radar (InSAR), or a variety of other instruments.

  4. Effect of initial plastic strain on mechanical training of non-modulated Ni–Mn–Ga martensite structure

    Energy Technology Data Exchange (ETDEWEB)

    Szczerba, M.J., E-mail: m.szczerba@imim.pl [Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta Street, 30-059 Kraków (Poland); Chulist, R. [Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta Street, 30-059 Kraków (Poland); Kopacz, S.; Szczerba, M.S. [Department of Materials Science and Non-Ferrous Metals Engineering, AGH University of Science and Technology, 30 Mickiewicza Ave., 30-059 Kraków (Poland)

    2014-08-12

    The influence of plastic pre-straining on the mechanical training process of Ni–Mn–Ga single crystals with a non-modulated martensite structure was examined using uniaxial quasi static compression tests and electron backscatter diffraction technique. Firstly, the optimal pre-straining temperature, for which a large plastic strain can be imposed to as-grown crystals with low flow stress and low rate of strain hardening, was established. Then, the maximum value of plastic pre-straining which allows performing successful room temperature mechanical training was found to be of about 20% of total sample thickness reduction. Below this value, training process leads to single variant state, which is able to accommodate true plastic strain of about 0.14 in each step of further training. Above 20% of deformation a multiple martensite variant state of characteristic triangular arrangements is generated. The latter structure cannot practically afford any plastic accommodation during further training; thus the training process fails to operate.

  5. Strain gradient polycrystal plasticity for micro-forming

    Science.gov (United States)

    Yalçinkaya, Tuncay; Simonovski, Igor; Özdemir, Izzet

    2016-10-01

    The developments in the micro-device industry has produced a substantial demand for the miniaturized metallic components with ultra-thin sheet materials that have thickness dimensions on the order of 50-500 µm which are produced through micro-forming processes. It is essential to have predictive tools to simulate the constitutive behavior of the materials at this length scale taking into account the physical and statistical size effect. Recent studies have shown that on the scale of several micrometers and below, crystalline materials behave differently from their bulk equivalent due to micro-structural effects (e.g. grain size, lattice defects and impurities), gradient effects (e.g. lattice curvature due to a non-uniform deformation field) and surface constraints (e.g. hard coatings or free interfaces). These effects could lead to stronger or weaker material response depending on the size and unique micro-structural features of the material. In this paper a plastic slip based strain gradient crystal plasticity model is used to address the effect of microstructural features (e.g. grain size, orientation and the number of grains) on the macroscopic constitutive response and the local behavior of polycrystalline materials.

  6. Strain hardening rate sensitivity and strain rate sensitivity in TWIP steels

    Energy Technology Data Exchange (ETDEWEB)

    Bintu, Alexandra [TEMA, Department of Mechanical Engineering, University of Aveiro, Campus Universitário de Santiago, 3810-193 (Portugal); Vincze, Gabriela, E-mail: gvincze@ua.pt [TEMA, Department of Mechanical Engineering, University of Aveiro, Campus Universitário de Santiago, 3810-193 (Portugal); Picu, Catalin R. [Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Lopes, Augusto B. [CICECO, Department of Materials and Ceramic Engineering, University of Aveiro, Campus Universitário de Santiago, 3810-193 (Portugal); Grácio, Jose J. [TEMA, Department of Mechanical Engineering, University of Aveiro, Campus Universitário de Santiago, 3810-193 (Portugal); Barlat, Frederic [Materials Mechanics Laboratory, Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of)

    2015-04-01

    TWIP steels are materials with very high strength and exceptional strain hardening capability, parameters leading to large energy absorption before failure. However, TWIP steels also exhibit reduced (often negative) strain rate sensitivity (SRS) which limits the post-necking deformation. In this study we demonstrate for an austenitic TWIP steel with 18% Mn a strong dependence of the twinning rate on the strain rate, which results in negative strain hardening rate sensitivity (SHRS). The instantaneous component of SHRS is large and negative, while its transient is close to zero. The SRS is observed to decrease with strain, becoming negative for larger strains. Direct observations of the strain rate dependence of the twinning rate are made using electron microscopy and electron backscatter diffraction, which substantiate the proposed mechanism for the observed negative SHRS.

  7. Computational procedures for finite deformation rate-independent plasticity and viscoplasticity based on overstress

    Science.gov (United States)

    Gomaa, Said Taha Khalil

    2000-10-01

    This thesis is dedicated to developing the computational procedures required in implementing the finite element method for finite deformation, rate-independent plasticity and finite deformation viscoplasticity theory based on overstress. The classical rate-independent, von Mises plasticity is formulated using both hypoelastic-plastic model and hyperelastic-plastic model. In the hypoelastic-plastic model, a relationship between an objective rate of Kirchhoff stress, based on a new recently proposed logarithmic spin [13], and the elastic part of rate of deformation tensor is postulated. In the hyperelastic-plastic model, the deformation gradient is decomposed into elastic and plastic deformations, a relationship between Kirchhoff stress and the logarithm of the elastic left stretch tensor is used. Numerical procedures for the integration of both models are developed. The isotropic, viscoplasticity theory based on overstress consisting of a flow law and two tensor valued and one scalar valued stress-like state variables is extended to finite deformation. To this end the Cauchy stress rate and the rates of the two tensor-valued state variables are interpreted as Eulerian tensors. The rate of deformation is equal to the sum of the elastic (the rate form of Hooke's law) and the inelastic rate of deformation, which depends on the overstress. The model does not contain a strain like quantity. Two integration schemes are considered: (i) a one step time integration scheme based on the forward gradient approximation and (ii) unconditionally stable implicit integration scheme based on backward Euler. The finite deformation, anisotropic, viscoplasticity theory based on overstress is formulated. A hypoelastic relation between the Lagrangian, rotated, logarithmic Cauchy stress rate and the rotated rate of deformation is used. The deformation induced anisotropy is modeled using a compliance tensor that allowed to grow according to Armstrong-Frederick law for fourth order tensors

  8. A work-hardening and softening constitutive model for sand: modified plastic strain energy approach

    Institute of Scientific and Technical Information of China (English)

    Fangle Peng; M.S.A. Siddiquee; Shaoming Liao

    2005-01-01

    The paper describes an energy-based constitutive model for sand, which is modified based on the modified plastic strain energy approach, represented by a unique relationship between the modified plastic strain energy and a stress parameter, independent of stress history. The modified plastic strain energy approach was developed based on results from a series of drained plastic strain compression tests along various stress paths on saturated dense Toyoura sand with accurate stress and strain measurements. The proposed model is coupled with an isotropically work-hardening and softening, non-associtated, elasto-plastic material description. The constitutive model concerns the inherent and stress systeminduced cross-anisotropic elastic deformation properties of sand. It is capable of simulating the deformation characteristics of stress history and stress path, the effects of pressure level, anisotropic strength and void ratio, and the strain localization.

  9. Plastic Strain Induced Damage Evolution and Martensitic Transformation in Ductile Materials at Cryogenic Temperatures

    CERN Document Server

    Garion, C

    2002-01-01

    The Fe-Cr-Ni stainless steels are well known for their ductile behaviour at cryogenic temperatures. This implies development and evolution of plastic strain fields in the stainless steel components subjected to thermo-mechanical loads at low temperatures. The evolution of plastic strain fields is usually associated with two phenomena: ductile damage and strain induced martensitic transformation. Ductile damage is described by the kinetic law of damage evolution. Here, the assumption of isotropic distribution of damage (microcracks and microvoids) in the Representative Volume Element (RVE) is made. Formation of the plastic strain induced martensite (irreversible process) leads to the presence of quasi-rigid inclusions of martensite in the austenitic matrix. The amount of martensite platelets in the RVE depends on the intensity of the plastic strain fields and on the temperature. The evolution of the volume fraction of martensite is governed by a kinetic law based on the accumulated plastic strain. Both of thes...

  10. Dynamic recrystallization of electroformed copper liners of shaped charges in high—strain—rate plastic deformation

    Institute of Scientific and Technical Information of China (English)

    WenhuaiTian; QiSun; 等

    2002-01-01

    The microstructures in the electroformed copper liners of shaped charges after high-strain-rate plastic deformation were in vestigated by transmission microscopy(TEM).Meanwhile,the orientation distribution of the grains in the recovered slug was examined by the electron backscattering Kikuchi pattern(EBSP) technique.EBSP analysis illustrated that unlike the as-formed electroformed copper liners of shaped charges the grain orientations in the recovered slug are distributed along randomly all the directions after undergoing heavily strain deformation at high-strain rate.Optical microscopy shows a typical recrystallization structure,and TEM examination reveals dislocation cells existed in the thin foil specimen.These results indicate that dynamic recovery and recrystallization occur during this plastic deformation process,and the associated deformation temperature is considered to be higher than 0.6 times the melting point of copper.

  11. An alternative treatment of phenomenological higher-order strain-gradient plasticity theory

    DEFF Research Database (Denmark)

    Kuroda, Mitsutoshi; Tvergaard, Viggo

    2010-01-01

    strain is discussed, applying a dislocation theory-based consideration. Then, a differential equation for the equivalent plastic strain-gradient is introduced as an additional governing equation. Its weak form makes it possible to deduce and impose extra boundary conditions for the equivalent plastic...

  12. Effects of constraints on lattice re-orientation and strain in polycrystal plasticity simulations

    DEFF Research Database (Denmark)

    Haldrup, Martin Kristoffer; McGinty, R.D.; McDowell, D.L.

    2009-01-01

    Employing a rate-dependent crystal plasticity model implemented in a novel and fast algorithm, two instantiations of an OFHC copper microstructure have been simulated by FE modelling to 11% tensile engineering strain with two different sets of boundary conditions. Analysis of lattice rotations......, strain distributions and global stress–strain response show the effect of changing from free to periodic boundary conditions to be a perturbation of a response dictated by the microstructure. Average lattice rotation for each crystallographic grain has been found to be in fair agreement with Taylor......-constraint simulations while fine scale element-resolved analysis shows large deviations from this prediction. Locally resolved analysis shows the existence of large domains dominated by slip on only a few slip systems. The modelling results are discussed in the light of recent experimental advances with respect to 2...

  13. Citation Rate Predictors in the Plastic Surgery Literature.

    Science.gov (United States)

    Lopez, Joseph; Calotta, Nicholas; Doshi, Ankur; Soni, Ashwin; Milton, Jacqueline; May, James W; Tufaro, Anthony P

    The purpose of this study is to determine and characterize the scientific and nonscientific factors that influence the rate of article citation in the field of plastic surgery. Cross-sectional study. We reviewed all entries in Annals of Plastic Surgery and Journal of Plastic, Reconstructive, and Aesthetic Surgery from January 1, 2007 to December 31, 2007; and Plastic and Reconstructive Surgery from January 1, 2007 to December 31, 2008. All scientific articles were analyzed and several article characteristics were extracted. The number of citations at 5 years was collected as the outcome variable. A multivariable analysis was performed to determine which variables were associated with higher citations rates. A total of 2456 articles were identified of which only 908 fulfilled the inclusion criteria. Most studies were publications in the fields of reconstructive (26.3%) or pediatric/craniofacial (17.6%) surgery. The median number of citations 5 years from publication was 8. In the multivariable analysis, factors associated with higher citations rates were subspecialty field (p = 0.0003), disclosed conflict of interest (p = 0.04), number of authors (p = 0.04), and journal (p = 0.02). We have found that higher level of evidence (or other study methodology factors) is not associated with higher citation rates. Instead, conflict of interest, subspecialty topic, journal, and number of authors are strong predictors of high citation rates in plastic surgery. Copyright © 2017 Association of Program Directors in Surgery. Published by Elsevier Inc. All rights reserved.

  14. Strain rate and temperature dependent mechanical behavior of nanocrystalline gold

    Science.gov (United States)

    Karanjgaokar, Nikhil J.

    by about 50% due to the extended temperature gradient along the specimen gauge section that causes plastic strain localization. On the contrary, the microheater based uniform heating method results in uniform temperature and strain fields during tensile experiments and was more suited for experiments at elevated temperatures. This uniform heating method was applied to annealed Au films with average grain size of 64 nm and for strain rates 10-5-10 s-1 , and temperatures 298-383 K. Activation volume calculations based on the combined temperature and strain rate experimental results pointed to two rate limiting mechanisms of inelastic deformation: Creep-driven and dislocation-mediated plasticity, with the transition occurring at increasing strain rates for increasing temperatures. The activation volume for the creep-dominated regime increased monotonically from 6.4b3 to 29.5b3 between 298 and 383 K, signifying GB diffusion processes and dislocation-mediated creep, respectively. The trends in the dislocationmediated plasticity regime followed an abnormally decreasing trend in the activation volume values with temperature, which was explained by a model for thermally activated dislocation depinning. Furthermore, the experimental data allowed us to evaluate the hardening behavior for Au films and model it using a linear hardening law and exponential relationships for the state variable and the saturation stress. The creep response of nanocrystalline Au films with 40 nm grain size was also obtained experimentally in an effort to assess its contribution to the overall mechanical response under uniaxial tension. Unusually high primary creep rates (3.3 x 10-8 to 2.7 x 10-7 s-1) and steady state creep rates (5.5 x 10-9 - 1.1 x 10-8 s-1) were measured with the primary creep regime lasting up to 5-6 hr for some stress amplitudes. A non-linear model based on the kinetics of thermal activation was applied to model the creep behavior of Au films, which captured very well the effect

  15. Analysis of a strain rate field in cold formed material using the visioplasticity method

    Directory of Open Access Journals (Sweden)

    L. Gusel

    2009-04-01

    Full Text Available In this paper the visioplasticity method is used to find the complete velocity and strain rate distributions from the experimental data, using the finite-difference method. The data about values of strain rates in plastic region of the material is very important for calculating stresses and the prediction of product quality. Specimens of copper alloy were extruded with different lubricants and different coefficients of friction and then the strain rate distributions were analysed and compared. Significant differences in velocity and strain rate distributions were obtained in some regions at the exit of the deformed zone.

  16. High Strain Rate Characterisation of Composite Materials

    DEFF Research Database (Denmark)

    Eriksen, Rasmus Normann Wilken

    The high strain rate characterisation of FRP materials present the experimenter with a new set of challenges in obtaining valid experimental data. These challenges were addressed in this work with basis in classic wave theory. The stress equilibrium process for linear elastic materials, as fibre...... a linear elastic specimen to reach a state of constant strain rate before fracture. This was in contrast to ductile materials, which are widely tested with for the High-speed servohydraulic test machine. The development of the analysis and the interpretation of the results, were based on the experience...

  17. Features of plastic strain localization at the yield plateau in Hadfield steel single crystals

    Science.gov (United States)

    Barannikova, S. A.; Zuev, L. B.

    2008-07-01

    Spatiotemporal distributions of local components of the plastic distortion tensor in Hadfield steel single crystals oriented for single twinning have been studied under active tensile straining conditions using the double-exposure speckle photography technique. Features of the macroscopically inhomogeneous strain localization at the yield plateau are considered. Relations between local components of the plastic distortion tensor in the zone of strain localization are analyzed.

  18. High strain rate behaviour of polypropylene microfoams

    Science.gov (United States)

    Gómez-del Río, T.; Garrido, M. A.; Rodríguez, J.; Arencón, D.; Martínez, A. B.

    2012-08-01

    Microcellular materials such as polypropylene foams are often used in protective applications and passive safety for packaging (electronic components, aeronautical structures, food, etc.) or personal safety (helmets, knee-pads, etc.). In such applications the foams which are used are often designed to absorb the maximum energy and are generally subjected to severe loadings involving high strain rates. The manufacture process to obtain polymeric microcellular foams is based on the polymer saturation with a supercritical gas, at high temperature and pressure. This method presents several advantages over the conventional injection moulding techniques which make it industrially feasible. However, the effect of processing conditions such as blowing agent, concentration and microfoaming time and/or temperature on the microstructure of the resulting microcellular polymer (density, cell size and geometry) is not yet set up. The compressive mechanical behaviour of several microcellular polypropylene foams has been investigated over a wide range of strain rates (0.001 to 3000 s-1) in order to show the effects of the processing parameters and strain rate on the mechanical properties. High strain rate tests were performed using a Split Hopkinson Pressure Bar apparatus (SHPB). Polypropylene and polyethylene-ethylene block copolymer foams of various densities were considered.

  19. High strain rate behaviour of polypropylene microfoams

    Directory of Open Access Journals (Sweden)

    Martínez A.B.

    2012-08-01

    Full Text Available Microcellular materials such as polypropylene foams are often used in protective applications and passive safety for packaging (electronic components, aeronautical structures, food, etc. or personal safety (helmets, knee-pads, etc.. In such applications the foams which are used are often designed to absorb the maximum energy and are generally subjected to severe loadings involving high strain rates. The manufacture process to obtain polymeric microcellular foams is based on the polymer saturation with a supercritical gas, at high temperature and pressure. This method presents several advantages over the conventional injection moulding techniques which make it industrially feasible. However, the effect of processing conditions such as blowing agent, concentration and microfoaming time and/or temperature on the microstructure of the resulting microcellular polymer (density, cell size and geometry is not yet set up. The compressive mechanical behaviour of several microcellular polypropylene foams has been investigated over a wide range of strain rates (0.001 to 3000 s−1 in order to show the effects of the processing parameters and strain rate on the mechanical properties. High strain rate tests were performed using a Split Hopkinson Pressure Bar apparatus (SHPB. Polypropylene and polyethylene-ethylene block copolymer foams of various densities were considered.

  20. Volume dilatation in a polycarbonate blend at varying strain rates

    Science.gov (United States)

    Hiermaier, S.; Huberth, F.

    2012-05-01

    Impact loaded polymers show a variety of strain-rate dependent mechanical properties in their elastic, plastic and failure behaviour. In contrast to purely crystalline materials, the volume of polymeric materials can significantly change under irreversible deformations. In this paper, uni-axial tensile tests were performed in order to measure the dilatation in the Polycarbonate-Acrylnitril-Butadien-Styrol (PC-ABS) Bayblend T65. The accumulation of dilatation was measured at deformation speeds of 0.1 and 500 [ mm/ s]. Instrumented with a pair of two high-speed cameras, volume segments in the samples were observed. The change in volume was quantified as relation between the deformed and initial volumes of the segments. It was observed that the measured dilatations are of great significance for the constitutive models. This is specifically demonstrated through comparisons of stress-strain relations derived from the two camera-perspectives with isochoric relations based on single-surface observations of the same experiments.

  1. Strain rate effects for spallation of concrete

    Directory of Open Access Journals (Sweden)

    Häussler-Combe Ulrich

    2015-01-01

    Full Text Available Appropriate triaxial constitutive laws are the key for a realistic simulation of high speed dynamics of concrete. The strain rate effect is still an open issue within this context. In particular the question whether it is a material property – which can be covered by rate dependent stress strain relations – or mainly an effect of inertia is still under discussion. Experimental and theoretical investigations of spallation of concrete specimen in a Hopkinson Bar setup may bring some evidence into this question. For this purpose the paper describes the VERD model, a newly developed constitutive law for concrete based on a damage approach with included strain rate effects [1]. In contrast to other approaches the dynamic strength increase is not directly coupled to strain rate values but related to physical mechanisms like the retarded movement of water in capillary systems and delayed microcracking. The constitutive law is fully triaxial and implemented into explicit finite element codes for the investigation of a wide range of concrete structures exposed to impact and explosions. The current setup models spallation experiments with concrete specimen [2]. The results of such experiments are mainly related to the dynamic tensile strength and the crack energy of concrete which may be derived from, e.g., the velocity of spalled concrete fragments. The experimental results are compared to the VERD model and two further constitutive laws implemented in LS-Dyna. The results indicate that both viscosity and retarded damage are required for a realistic description of the material behaviour of concrete exposed to high strain effects [3].

  2. Theoretical and numerical study of strain localization under high strain rate solicitation

    Science.gov (United States)

    Ranc, N.; Raynal, R.; Taravella, L.; Pina, V.; Hervé, P.

    2006-08-01

    Our study deals with the dynamic behavior of metallic materials and in particular of titanium alloy TA6V. For high strain rates, we can notice the occurrence of a phenomenon called adiabatic shearing. This phenomenon is about a plastic instability, which results in the appearance of a strain localization in narrow bands. In this paper we developed a thermo mechanical model to reproduce the formation and the propagation of adiabatic shear bands. A Johnson Cook thermo visco plastic behavior law was chosen for the titanium alloy TA6V. The law parameters were identified from static and dynamic torsion tests at various temperatures between ambient and 350circC. A 2D numerical simulation of torsion test was performed with the explicit finite elements code Abaqus. The thermo mechanical coupling and the heat conduction are taken into account. A roughness defect was inserted in the centre of a torsion specimen. The results showed that the strain of localization and the shear band speed increase when the amplitude and the size of the defect decrease.

  3. Bounds on the Rate Dependent Plastic Flow of Tantalum up to 75 GPa

    Science.gov (United States)

    Reed, Bryan; Patterson, Reed; Kumar, Mukul

    2013-06-01

    We report improvements in a general thermodynamics-based velocimetry analysis method designed to extract strength and plastic-flow information from shock and ramp compression experiments. The method allows extraction of thermodynamic histories, including deviatoric stress and plastic strain, including nonsteady rate-dependent features. The improved method includes free-surface corrections for pullback waves, reduced noise sensitivity, and application to pressures of 75 GPa and higher. Specifically, we show results for shock waves in tantalum, including bounds on the plastic flow behavior at strain rates exceeding 1e7/s.The deviatoric stress appears to be almost entirely dependent on strain rate, with very little pressure dependence.The deviatoric stress in the post-shock plateau state appears to be very small at higher pressures, calling into question the value of considering strength as a steady- state pressure-dependent quantity. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  4. Neutron-diffraction measurement of the evolution of strain for non-uniform plastic deformation

    CERN Document Server

    Rogge, R B; Boyce, D

    2002-01-01

    Neutrons are particularly adept for the validation of modeling predictions of stress and strain. In recent years, there has been a significant effort to model the evolution of both the macroscopic stresses and the intergranular stress during plastic deformation. These have had broad implications with regard to understanding the evolution of residual stress and to diffraction-based measurements of strain. Generally the modeling and associated measurements have been performed for simple uniaxial tension, leaving questions with regard to plastic deformation under multi-axial stress and non-uniform stress. Extensive measurements of the strain profile across a plastic hinge for each of a series of loading and unloading cycles to progressively higher degrees of plastic deformation are presented. These measurements are used to assess multiple-length-scale finite-element modeling (FEM) of the plastic hinge, in which the elements will range in size from single crystallites (as used in successful simulations of uniaxia...

  5. High Strain Rate Compression Testing of Ceramics and Ceramic Composites.

    Energy Technology Data Exchange (ETDEWEB)

    Blumenthal, W. R. (William R.)

    2005-01-01

    The compressive deformation and failure behavior of ceramics and ceramic-metal composites for armor applications has been studied as a function of strain rate at Los Alamos National Laboratory since the late 1980s. High strain rate ({approx}10{sup 3} s{sup -1}) uniaxial compression loading can be achieved using the Kolsky-split-Hopkinson pressure bar (SHPB) technique, but special methods must be used to obtain valid strength results. This paper reviews these methods and the limitations of the Kolsky-SHPB technique for this class of materials. The Kolsky-split-Hopkinson pressure bar (Kolsky-SHPB) technique was originally developed to characterize the mechanical behavior of ductile materials such as metals and polymers where the results can be used to develop strain-rate and temperature-dependent constitutive behavior models that empirically describe macroscopic plastic flow. The flow behavior of metals and polymers is generally controlled by thermally-activated and rate-dependent dislocation motion or polymer chain motion in response to shear stresses. Conversely, the macroscopic mechanical behavior of dense, brittle, ceramic-based materials is dominated by elastic deformation terminated by rapid failure associated with the propagation of defects in the material in response to resolved tensile stresses. This behavior is usually characterized by a distribution of macroscopically measured failure strengths and strains. The basis for any strain-rate dependence observed in the failure strength must originate from rate-dependence in the damage and fracture process, since uniform, uniaxial elastic behavior is rate-independent (e.g. inertial effects on crack growth). The study of microscopic damage and fracture processes and their rate-dependence under dynamic loading conditions is a difficult experimental challenge that is not addressed in this paper. The purpose of this paper is to review the methods that have been developed at the Los Alamos National Laboratory to

  6. Effects of Adiabatic Heating on the High Strain Rate Deformation of Polymer Matrix Composites

    Science.gov (United States)

    Sorini, Chris; Chattopadhyay, Aditi; Goldberg, Robert K.

    2017-01-01

    Polymer matrix composites (PMCs) are increasingly being used in aerospace structures that are expected to experience complex dynamic loading conditions throughout their lifetime. As such, a detailed understanding of the high strain rate behavior of the constituents, particularly the strain rate, temperature, and pressure dependent polymer matrix, is paramount. In this paper, preliminary efforts in modeling experimentally observed temperature rises due to plastic deformation in PMCs subjected to dynamic loading are presented. To this end, an existing isothermal viscoplastic polymer constitutive formulation is extended to model adiabatic conditions by incorporating temperature dependent elastic properties and modifying the components of the inelastic strain rate tensor to explicitly depend on temperature. It is demonstrated that the modified polymer constitutive model is capable of capturing strain rate and temperature dependent yield as well as thermal softening associated with the conversion of plastic work to heat at high rates of strain. The modified constitutive model is then embedded within a strength of materials based micromechanics framework to investigate the manifestation of matrix thermal softening, due to the conversion of plastic work to heat, on the high strain rate response of a T700Epon 862 (T700E862) unidirectional composite. Adiabatic model predictions for high strain rate composite longitudinal tensile, transverse tensile, and in-plane shear loading are presented. Results show a substantial deviation from isothermal conditions; significant thermal softening is observed for matrix dominated deformation modes (transverse tension and in-plane shear), highlighting the importance of accounting for the conversion of plastic work to heat in the polymer matrix in the high strain rate analysis of PMC structures.

  7. Strain gradient plasticity modeling of hydrogen diffusion to the crack tip

    DEFF Research Database (Denmark)

    Martínez Pañeda, Emilio; del Busto, S.; Niordson, Christian Frithiof

    2016-01-01

    In this work hydrogen diffusion towards the fracture process zone is examined accounting for local hardening due to geometrically necessary dislocations (GNDs) by means of strain gradient plasticity (SGP). Finite element computations are performed within the finite deformation theory...

  8. Plasticity dependent damage evolution in composites with strain-gradient effects

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang

    2015-01-01

    A unit cell approach is adopted to numerically analyze the effect of reinforcement size on fracture evolution in metal matrix composites. The matrix material shows plastic size-effects and is modeled by an anisotropic version of the single parameter strain-gradient (higher-order) plasticity model...

  9. CYCLIC PLASTIC BEHAVIOUR OF UFG COPPER UNDER CONTROLLED STRESS AND STRAIN LOADING

    Directory of Open Access Journals (Sweden)

    Lucie Navrátilová

    2012-01-01

    Full Text Available The influence of stress- and strain-controlled loading on microstructure and cyclic plastic behaviour of ultrafine-grained copper prepared by equal channel angular pressing was examined. The stability of microstructure is a characteristic feature for stress-controlled test whereas grain coarsening and development of bimodal structure was observed after plastic strain-controlled tests. An attempt to explain the observed behaviour was made.

  10. A two-speed model for finite-strain elasto-plasticity

    OpenAIRE

    Rindler, Filip

    2015-01-01

    This work presents a new modeling approach to macroscopic, polycrystalline elasto-plasticity starting from first principles and a few well-defined structural assumptions, incorporating the mildly rate-dependent (viscous) nature of plastic flow and the microscopic origins of plastic deformations. For the global dynamics, we start from a two-stage time-stepping scheme, expressing the fact that in most real materials plastic flow is much slower than elastic deformations, and then perform a detai...

  11. Shock Compression and Strain Rate Effect in Composites and Polymers

    Energy Technology Data Exchange (ETDEWEB)

    Brown, Eric [Los Alamos National Laboratory

    2012-06-20

    Polymers are increasingly being utilized as monolithic materials and composite matrices for structural applications historically reserved for metals. High strain and high strain-rate applications in aerospace, defense, and automotive industries have lead to interest in utilizing the ability of many polymers to withstand extensions to failure of several hundred percent, often without localization or necking and their strong rate dependence. A broad range of characterization techniques will be presented for semi-crystalline polymers and composites including elastic-plastic fracture, split Hopkinson pressure bar (SHPB), plate impact including soft-recovery and lateral gage measurements and Taylor Impact. Gas-launched, plate impact experiments have been performed on pedigreed PTFE 7C, mounted in momentum-trapped, shock assemblies, with impact pressures above and below the phase II to phase III crystalline transition to probe subtle changes in the crystallinity, microstructure, and mechanical response of PTFE. Observed strong anisotropy on the hugoniot and spall behavior of fiber-reinforced composites will be discussed. Polymers are known to exhibit a strong dependence of the yield stress on temperature and strain-rate that are often observed to be linear for temperature and logarithmic for strain-rate. Temperature and strain-rate dependence will be reviewed in terms of classic time-temperature superposition and an empirical mapping function for superposition between temperature and strain-rate. The recent extension of the new Dynamic-Tensile-Extrusion (Dyn-Ten-Ext) technique to probe the dynamic tensile responses of polymers will be discussed, where more irregular deformation and stochastic-based damage and failure mechanisms than the stable plastic elongation and shear instabilities observed that in metals. The opportunity to use of Dyn-Ten-Ext to probe incipient damage at very high strain-rate by linking in situ and post mortem experimental observations with high

  12. Slip transfer and plastic strain accumulation across grain boundaries in Hastelloy X

    Science.gov (United States)

    Abuzaid, Wael Z.; Sangid, Michael D.; Carroll, Jay D.; Sehitoglu, Huseyin; Lambros, John

    2012-06-01

    In this study, high resolution ex situ digital image correlation (DIC) was used to measure plastic strain accumulation with sub-grain level spatial resolution in uniaxial tension of a nickel-based superalloy, Hastelloy X. In addition, the underlying microstructure was characterized with similar spatial resolution using electron backscatter diffraction (EBSD). With this combination of crystallographic orientation data and plastic strain measurements, the resolved shear strains on individual slip systems were spatially calculated across a substantial region of interest, i.e., we determined the local slip system activity in an aggregate of ˜600 grains and annealing twins. The full-field DIC measurements show a high level of heterogeneity in the plastic response with large variations in strain magnitudes within grains and across grain boundaries (GBs). We used the experimental results to study these variations in strain, focusing in particular on the role of slip transmission across GBs in the development of strain heterogeneities. For every GB in the polycrystalline aggregate, we have established the most likely dislocation reaction and used that information to calculate the residual Burgers vector and plastic strain magnitudes due to slip transmission across each interface. We have also used molecular dynamics simulations (MD) to establish the energy barriers to slip transmission for selected cases yielding different magnitudes of the residual Burgers vector. From our analysis, we show an inverse relation between the magnitudes of the residual Burgers vector and the plastic strains across GBs. Also, the MD simulations reveal a higher energy barrier for slip transmission at high magnitudes of the residual Burgers vector. We therefore emphasize the importance of considering the magnitude of the residual Burgers vector to obtain a better description of the GB resistance to slip transmission, which in turn influences the local plastic strains in the vicinity of grain

  13. Prediction of thermal strains in fibre reinforced plastic matrix by discretisation of the temperature exposure history

    Science.gov (United States)

    Ngoy, E. K.

    2016-07-01

    Prediction of environmental effects on fibre reinforced plastics habitually is made difficult due to the complex variability of the natural service environment. This paper suggests a method to predict thermal strain distribution over the material lifetime by discretisation of the exposure history. Laboratory results show a high correlation between predicted and experimentally measured strain distribution

  14. Numerical treatment of cosserat based rate independent strain gradient plasticity theories Tratamiento numérico de una teoría de plasticidad por gradiente de deformación basada en un modelo de cosserat

    Directory of Open Access Journals (Sweden)

    Juan David Gómez C.

    2008-12-01

    Full Text Available The current trend towards miniaturization in the microelectronics industryhas pushed for the development of theories intended to explain the behaviorof materials at small scales. In the particular case of metals, a class ofavailable non–classical continuum mechanics theories has been recently employedin order to explain the wide range of observed behavior at the micronscale. The practical use of the proposed theories remains limited due to issuesin its numerical implementation. First, in displacement–based finite elementformulations the need appears for higher orders of continuity in the interpolationshape functions in order to maintain the convergence rate upon meshrefinement. This limitation places strong restrictions in the geometries of theavailable elements. Second, the available inelastic constitutive models for smallscale applications have been cast into deformation theory formulations limitingthe set of problems to those exhibiting proportional loading only. In thisarticle two contributions are made for the particular case of a Cosserat couplestress continuum. First it describes a numerical scheme based on a penaltyfunction/reduced integration approach that allows for the proper treatment ofthe higher order terms present in Cosserat like theories. This scheme results in a new finite element that can be directly implemented into commercial finiteelement codes. Second, a flow theory of plasticity incorporating size effects isproposed for the case of rate independent materials overcoming the limitationsin the deformation theory formulations. The constitutive model and its correspondingtime–integration algorithm are coupled to the new proposed finiteelement and implemented in the form of a user element subroutine into thecommercial code ABAQUS. The validity of the approach is shown via numericalsimulations of the microbending experiment on thin Nickel foils reportedin the literature.La tendencia actual hacia la miniaturización en la

  15. Suppressed plastic deformation at blunt crack tips due to strain gradient effects

    DEFF Research Database (Denmark)

    Mikkelsen, Lars Pilgaard; Goutianos, Stergios

    2009-01-01

    Large deformation gradients occur near a crack-tip and strain gradient dependent crack-tip deformation and stress fields are expected. Nevertheless, for material length scales much smaller than the scale of the deformation gradients, a conventional elastic-plastic solution is obtained. On the other...... hand, for significant large material length scales, a conventional elastic solution is obtained. This transition in behaviour is investigated based on a finite strain version of the Fleck-Hutchinson strain gradient plasticity model from 2001. The predictions show that for a wide range of material...

  16. Finite element implementation and numerical issues of strain gradient plasticity with application to metal matrix composites

    DEFF Research Database (Denmark)

    Frederiksson, Per; Gudmundson, Peter; Mikkelsen, Lars Pilgaard

    2009-01-01

    A framework of finite element equations for strain gradient plasticity is presented. The theoretical framework requires plastic strain degrees of freedom in addition to displacements and a plane strain version is implemented into a commercial finite element code. A couple of different elements...... of quadrilateral type are examined and a few numerical issues are addressed related to these elements as well as to strain gradient plasticity theories in general. Numerical results are presented for an idealized cell model of a metal matrix composite under shear loading. It is shown that strengthening due...... to fiber size is captured but strengthening due to fiber shape is not. A few modelling aspects of this problem are discussed as well. An analytic solution is also presented which illustrates similarities to other theories....

  17. Mode I and mixed mode crack-tip fields in strain gradient plasticity

    DEFF Research Database (Denmark)

    Goutianos, Stergios

    2011-01-01

    Strain gradients develop near the crack-tip of Mode I or mixed mode cracks. A finite strain version of the phenomenological strain gradient plasticity theory of Fleck–Hutchinson (2001) is used here to quantify the effect of the material length scales on the crack-tip stress field for a sharp...... stationary crack under Mode I and mixed mode loading. It is found that for material length scales much smaller than the scale of the deformation gradients, the predictions converge to conventional elastic–plastic solutions. For length scales sufficiently large, the predictions converge to elastic solutions....... Thus, the range of length scales over which a strain gradient plasticity model is necessary is identified. The role of each of the three material length scales, incorporated in the multiple length scale theory, in altering the near-tip stress field is systematically studied in order to quantify...

  18. Strain Hardening of Polymer Glasses: Entanglements, Energetics, and Plasticity

    OpenAIRE

    Hoy, Robert S.; Robbins, Mark O.

    2007-01-01

    Simulations are used to examine the microscopic origins of strain hardening in polymer glasses. While stress-strain curves for a wide range of temperature can be fit to the functional form predicted by entropic network models, many other results are fundamentally inconsistent with the physical picture underlying these models. Stresses are too large to be entropic and have the wrong trend with temperature. The most dramatic hardening at large strains reflects increases in energy as chains are ...

  19. Tensile Properties of TWIP Steel at High Strain Rate

    Institute of Scientific and Technical Information of China (English)

    XIONG Rong-gang; FU Ren-yu; SU Yu; LI Qian; WEI Xi-cheng; LI Lin

    2009-01-01

    Tensile tests of TWIP steels of two compositions are performed in the strain rate range of 10-5 -103 s-1.Results indicate that steel 1# does not exhibit TWIP effect but deformation-induced martensitic transformation appears only.There exists TWIP effect in steel 3#.Tensile properties at room temperature are sensitive to strain rate in the studied strain rate ranges.Analysis on the relationship between strain-hardening exponent and strain rates shows that strain-induced martensitic transformation and formation of twins during deformation have significant influence on their strain-hardening behavior.

  20. Tantalum strength model incorporating temperature, strain rate and pressure

    Science.gov (United States)

    Lim, Hojun; Battaile, Corbett; Brown, Justin; Lane, Matt

    Tantalum is a body-centered-cubic (BCC) refractory metal that is widely used in many applications in high temperature, strain rate and pressure environments. In this work, we propose a physically-based strength model for tantalum that incorporates effects of temperature, strain rate and pressure. A constitutive model for single crystal tantalum is developed based on dislocation kink-pair theory, and calibrated to measurements on single crystal specimens. The model is then used to predict deformations of single- and polycrystalline tantalum. In addition, the proposed strength model is implemented into Sandia's ALEGRA solid dynamics code to predict plastic deformations of tantalum in engineering-scale applications at extreme conditions, e.g. Taylor impact tests and Z machine's high pressure ramp compression tests, and the results are compared with available experimental data. Sandia National Laboratories is a multi program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  1. High strain rate characterization of polymers

    Science.gov (United States)

    Siviour, Clive R.

    2017-01-01

    This paper reviews the literature on the response of polymers to high strain rate deformation. The main focus is on the experimental techniques used to characterize this response. The paper includes a small number of examples as well as references to experimental data over a wide range of rates, which illustrate the key features of rate dependence in these materials; however this is by no means an exhaustive list. The aim of the paper is to give the reader unfamiliar with the subject an overview of the techniques available with sufficient references from which further information can be obtained. In addition to the `well established' techniques of the Hopkinson bar, Taylor Impact and Transverse impact, a discussion of the use of time-temperature superposition in interpreting and experimentally replicating high rate response is given, as is a description of new techniques in which mechanical parameters are derived by directly measuring wave propagation in specimens; these are particularly appropriate for polymers with low wave speeds. The vast topic of constitutive modelling is deliberately excluded from this review.

  2. Effect of strain rates on deformation behaviors of an in situ Ti-based metallic glass matrix composite

    Science.gov (United States)

    Jiao, Z. M.; Wang, Z. H.; Chu, M. Y.; Wang, Y. S.; Yang, H. J.; Qiao, J. W.

    2016-06-01

    Quasi-static and dynamic deformation behaviors of an in situ dendrite-reinforced metallic glass matrix composite: Ti56Zr18V10Cu4Be12 were investigated. Upon quasi-static compression, the composite exhibits distinguished work hardening, accompanied by the ultimate strength of 1290 MPa and the plasticity of 20 %. The improved plasticity is attributed to the multiplication of shear bands within the glass matrix and pileups of dislocations within the dendrites. Upon dynamic compression, the stable plastic flow prevails and the yielding stress increases with the strain rate. The macroscopic plasticity decreases considerably, since the shear bands cannot be effectively hindered by dendrites with deteriorated toughness. The dendrite-dominated mechanism results in the positive strain-rate sensitivity, and the Cowper-Symonds model is employed to depict the strain-rate dependency of yielding strength.

  3. Isogeometric Analysis of Nearly Incompressible Large Strain Plasticity

    Science.gov (United States)

    2011-11-01

    distribution unlimited 13. SUPPLEMENTARY NOTES 14. ABSTRACT We study the behavior of NURBS -based Isogeometric Analysis on problems of large-deformation...plasticity. We evaluate the performance of standard NURBS elements and elements based on the F formulation of Elguedj et al. (T. Elguedj, Y. Bazilevs... NURBS elements, Com- puter Methods in Applied Mechanics and Engineering, 197 (2008), 2732{2762). We determine that standard measures of evaluation

  4. High strain rate deformation of layered nanocomposites

    Science.gov (United States)

    Lee, Jae-Hwang; Veysset, David; Singer, Jonathan P.; Retsch, Markus; Saini, Gagan; Pezeril, Thomas; Nelson, Keith A.; Thomas, Edwin L.

    2012-11-01

    Insight into the mechanical behaviour of nanomaterials under the extreme condition of very high deformation rates and to very large strains is needed to provide improved understanding for the development of new protective materials. Applications include protection against bullets for body armour, micrometeorites for satellites, and high-speed particle impact for jet engine turbine blades. Here we use a microscopic ballistic test to report the responses of periodic glassy-rubbery layered block-copolymer nanostructures to impact from hypervelocity micron-sized silica spheres. Entire deformation fields are experimentally visualized at an exceptionally high resolution (below 10 nm) and we discover how the microstructure dissipates the impact energy via layer kinking, layer compression, extreme chain conformational flattening, domain fragmentation and segmental mixing to form a liquid phase. Orientation-dependent experiments show that the dissipation can be enhanced by 30% by proper orientation of the layers.

  5. Strain rate dependency of oceanic intraplate earthquake b-values at extremely low strain rates

    Science.gov (United States)

    Sasajima, Ryohei; Ito, Takeo

    2016-06-01

    We discovered a clear positive dependence of oceanic intraplate earthquake (OCEQ) b-values on the age of the oceanic lithosphere. OCEQ b-values in the youngest (20 Ma) oceanic lithosphere exceed 1.5, which is significantly higher than the average worldwide earthquake b-value (around 1.0). On the other hand, the b-value of intraplate earthquakes in the Ninety East-Sumatra orogen, where oceanic lithosphere has an anomalously higher strain rate compared with normal oceanic lithosphere, is 0.93, which is significantly lower than the OCEQ b-value (about 1.9) with the same age (50-110 Ma). Thus, the variation in b-values relates to the strain rate of the oceanic lithosphere and is not caused by a difference in thermal structure. We revealed a negative strain rate dependency of the b-value at extremely low strain rates (1.5) in oceanic lithosphere >20 Ma old imply that future improvement in seismic observation will capture many smaller magnitude OCEQs, which will provide valuable information on the evolution of the oceanic lithosphere and the driving mechanism of plate tectonics.

  6. The development of strain anisotropy during plastic deformation of an aluminium polycrystal

    Energy Technology Data Exchange (ETDEWEB)

    Korsunsky, A.M. [Oxford Univ. (United Kingdom). Dept. of Engineering Science; Daymond, M.R. [ISIS Facility, Rutherford Appleton Lab., Chilton, Oxon (United Kingdom); Wells, K.E. [Dept. of Mechanical, Materials and Mfg. Engineering, Univ. of Newcastle (United Kingdom)

    2000-07-01

    To measure internal strains in an Al MMC, time-of-flight (TOF) neutron diffraction was used on the ENGIN instrument at ISIS, RAL, in Oxfordshire, and a monochromated X-ray beam was employed on the BM16 beamline at the ESRF in Grenoble. The development of intergranular stresses between groups of grains possessing certain crystallographic orientations was studied using diffraction of penetrating radiation. Due to aluminium's highly isotropic elastic modulus, the variation of measured strains in the alloy matrix with orientation can be attributed to the anisotropy of the crystal yield surface and plastic flow parameters. A simple illustrative model is presented which explains the observed correlation between the amount of plastic strain (PS) and the measured anisotropy strain (AS) values. In particular, the model explains why a linear relationship is observed between AS and PS for low strain values, and how saturation of AS sets in at higher imposed PS levels. (orig.)

  7. Identification of strain-rate and thermal sensitive material model with an inverse method

    CERN Document Server

    Peroni, L; Peroni, M

    2010-01-01

    This paper describes a numerical inverse method to extract material strength parameters from the experimental data obtained via mechanical tests at different strain-rates and temperatures. It will be shown that this procedure is particularly useful to analyse experimental results when the stress-strain fields in the specimen cannot be correctly described via analytical models. This commonly happens in specimens with no regular shape, in specimens with a regular shape when some instability phenomena occur (for example the necking phenomena in tensile tests that create a strongly heterogeneous stress-strain fields) or in dynamic tests (where the strain-rate field is not constant due to wave propagation phenomena). Furthermore the developed procedure is useful to take into account thermal phenomena generally affecting high strain-rate tests due to the adiabatic overheating related to the conversion of plastic work. The method presented requires strong effort both from experimental and numerical point of view, an...

  8. Compressive behavior of bulk metallic glass under different conditions --- Coupled effect of temperature and strain rate

    Science.gov (United States)

    Yin, Weihua

    Metallic glass was first reported in 1960 by rapid quenching of Au-Si alloys. But, due to the size limitation, this material did not attract remarkable interest until the development of bulk metallic glasses (BMGs) with specimen sizes in excess of 1 mm. BMGs are considered to be promising engineering materials because of their ultrahigh strength, high elastic limit and wear resistance. However, they usually suer from a strong tendency for localized plastic deformation with catastrophic failure. Many basic questions, such as the origin of shear softening and the strain rate eect remain unclear. In this thesis, the mechanical behavior of the Zr55Al 10Ni5Cu30 bulk metallic glass and a metallic glass composite is investigated. The stress-strain relationship for Zr55Al10Ni 5Cu30 over a wide range of strain rate (5x10 --5 to 2x103 s--1) was investigated in uniaxial compression loading using both MTS servo-hydraulic system (quasi-static) and compression Kolsky bar system (dynamic). The effect of the strain rate on the fracture stress at room temperature was discussed. Based on the experimental results, the strain rate sensitivity of the bulk metallic glass changes from a positive value to a negative value at high strain rate, which is a consequence of the significant adiabatic temperature rise during the dynamic testing. In order to characterize the temperature eect on the mechanical behavior of the metallic glass, a synchronically assembled heating unit was designed to be attached onto the Kolsky bar system to perform high temperature and high strain rate mechanical testing. A transition from inhomogeneous deformation to homogeneous deformation has been observed during the quasi-static compressive experiments at testing temperatures close to the glass transition temperature. However, no transition has been observed at high strain rates at all the testing temperatures. A free volume based model is applied to analyze the stress-strain behavior of the homogeneous

  9. Finite Element Modeling of the Behavior of Armor Materials Under High Strain Rates and Large Strains

    Science.gov (United States)

    Polyzois, Ioannis

    For years high strength steels and alloys have been widely used by the military for making armor plates. Advances in technology have led to the development of materials with improved resistance to penetration and deformation. Until recently, the behavior of these materials under high strain rates and large strains has been primarily based on laboratory testing using the Split Hopkinson Pressure Bar apparatus. With the advent of sophisticated computer programs, computer modeling and finite element simulations are being developed to predict the deformation behavior of these metals for a variety of conditions similar to those experienced during combat. In the present investigation, a modified direct impact Split Hopkinson Pressure Bar apparatus was modeled using the finite element software ABAQUS 6.8 for the purpose of simulating high strain rate compression of specimens of three armor materials: maraging steel 300, high hardness armor (HHA), and aluminum alloy 5083. These armor materials, provided by the Canadian Department of National Defence, were tested at the University of Manitoba by others. In this study, the empirical Johnson-Cook visco-plastic and damage models were used to simulate the deformation behavior obtained experimentally. A series of stress-time plots at various projectile impact momenta were produced and verified by comparison with experimental data. The impact momentum parameter was chosen rather than projectile velocity to normalize the initial conditions for each simulation. Phenomena such as the formation of adiabatic shear bands caused by deformation at high strains and strain rates were investigated through simulations. It was found that the Johnson-Cook model can accurately simulate the behavior of body-centered cubic (BCC) metals such as steels. The maximum shear stress was calculated for each simulation at various impact momenta. The finite element model showed that shear failure first occurred in the center of the cylindrical specimen and

  10. Distribution of energy storage rate in area of strain localization during tension of austenitic steel

    Science.gov (United States)

    Oliferuk, W.; Maj, M.; Zembrzycki, K.

    2015-01-01

    The present work is devoted to experimental determination of the energy storage rate in the area of strain localization. The experimental procedure involves two complementary techniques: i.e. infrared thermography (IRT) and visible light imaging. The results of experiments have shown that during the evolution of plastic strain localization the energy storage rate in some areas of the deformed specimen drops to zero. To interpret the decrease of the energy storage rate in terms of micro-mechanisms, microstructural observations using electron back scattered diffraction (EBSC) were performed.

  11. Strain rate and temperature effects on crack initiation of direct aged 718 Alloy

    Directory of Open Access Journals (Sweden)

    Perrais Maxime

    2014-01-01

    Full Text Available During mechanical tests at high temperature in an oxidizing atmosphere, the effects of strain rate on crack initiation are noticeable. This effect is due to a coupling between local mechanical loading and oxidation. Samples were machined in a turbine disk made of direct aged alloy 718. Tests were performed to understand the effect of these couplings on crack initiation and to ensure lifetime is optimized. This study compared the cracking resistance of two different specimen geometries at a given plastic strain and performed quantitative measurement of the mechanical loading conditions inducing crack initiation between 600 ∘C and 650 ∘C. Sample geometries consisted in tensile flat specimens and V-shaped samples. This specific geometry was used to localize strain and damage in the apex of the V and to reach strain rates lower than those possible on standard specimens. Digital image correlation technique was used to provide strain measurements. For each temperature and strain rate, finite element calculations using the identified constitutive law were performed to get a refined level of strain in different areas at the V apex. Tests were stopped after an imposed displacement corresponding to a given plastic strain distribution. SEM observations of the surface of the flat tensile samples revealed no crack initiation. On the contrary, SEM observations at the apex of V specimens for which the level of cumulative strain was close to the level of cumulative strain of flat samples reveal the presence of intergranular damage when the strain rate used was below a given level.

  12. Analytical Modeling of the High Strain Rate Deformation of Polymer Matrix Composites

    Science.gov (United States)

    Goldberg, Robert K.; Roberts, Gary D.; Gilat, Amos

    2003-01-01

    The results presented here are part of an ongoing research program to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. State variable constitutive equations originally developed for metals have been modified in order to model the nonlinear, strain rate dependent deformation of polymeric matrix materials. To account for the effects of hydrostatic stresses, which are significant in polymers, the classical 5 plasticity theory definitions of effective stress and effective plastic strain are modified by applying variations of the Drucker-Prager yield criterion. To verify the revised formulation, the shear and tensile deformation of a representative toughened epoxy is analyzed across a wide range of strain rates (from quasi-static to high strain rates) and the results are compared to experimentally obtained values. For the analyzed polymers, both the tensile and shear stress-strain curves computed using the analytical model correlate well with values obtained through experimental tests. The polymer constitutive equations are implemented within a strength of materials based micromechanics method to predict the nonlinear, strain rate dependent deformation of polymer matrix composites. In the micromechanics, the unit cell is divided up into a number of independently analyzed slices, and laminate theory is then applied to obtain the effective deformation of the unit cell. The composite mechanics are verified by analyzing the deformation of a representative polymer matrix composite (composed using the representative polymer analyzed for the correlation of the polymer constitutive equations) for several fiber orientation angles across a variety of strain rates. The computed values compare favorably to experimentally obtained results.

  13. A Model for High-Strain-Rate Deformation of Uranium-Niobium Alloys

    Energy Technology Data Exchange (ETDEWEB)

    F.L.Addessio; Q.H.Zuo; T.A.Mason; L.C.Brinson

    2003-05-01

    A thermodynamic approach is used to develop a framework for modeling uranium-niobium alloys under the conditions of high strain rate. Using this framework, a three-dimensional phenomenological model, which includes nonlinear elasticity (equation of state), phase transformation, crystal reorientation, rate-dependent plasticity, and porosity growth is presented. An implicit numerical technique is used to solve the evolution equations for the material state. Comparisons are made between the model and data for low-strain-rate loading and unloading as well as for heating and cooling experiments. Comparisons of the model and data also are made for low- and high-strain-rate uniaxial stress and uniaxial strain experiments. A uranium-6 weight percent niobium alloy is used in the comparisons of model and experiment.

  14. Derivation of Relations and Analysis of Tube Bending Processes Using Discontinuous Fields of Plastic Strains

    Science.gov (United States)

    Śloderbach, Z.

    2015-05-01

    The generalized strain scheme in bending metal tubes at bending machines with the use of a mandrel presented in Śloderbach (1999; 2002; 20131,2; 2014) satisfies initial and boundary kinematic conditions of bending, conditions of continuity and inseparability of strains. This paper introduces three formal simplifications gradually imposed into forms of principal components of the generalized strain model giving suitable simplifications of the 1st, 2nd and 3rd types. Such mathematical simplifications cause that the obtained strain fields do not satisfy the condition of consistency of displacements and strain continuity. The simplified methods determine safer values of the wall thickness than those from the generalized continuous strain scheme. The condition of plastic incompressibility was used for the derivation of an expression for distribution of wall thickness of the bent elbow in the layers subjected to tension and compression for three examples of discontinuous kinematic strain fields.

  15. Strain Rate Dependant Material Model for Orthotropic Metals

    Science.gov (United States)

    Vignjevic, Rade

    2016-08-01

    In manufacturing processes anisotropic metals are often exposed to the loading with high strain rates in the range from 102 s-1 to 106 s-1 (e.g. stamping, cold spraying and explosive forming). These types of loading often involve generation and propagation of shock waves within the material. The material behaviour under such a complex loading needs to be accurately modelled, in order to optimise the manufacturing process and achieve appropriate properties of the manufactured component. The presented research is related to development and validation of a thermodynamically consistent physically based constitutive model for metals under high rate loading. The model is capable of modelling damage, failure and formation and propagation of shock waves in anisotropic metals. The model has two main parts: the strength part which defines the material response to shear deformation and an equation of state (EOS) which defines the material response to isotropic volumetric deformation [1]. The constitutive model was implemented into the transient nonlinear finite element code DYNA3D [2] and our in house SPH code. Limited model validation was performed by simulating a number of high velocity material characterisation and validation impact tests. The new damage model was developed in the framework of configurational continuum mechanics and irreversible thermodynamics with internal state variables. The use of the multiplicative decomposition of deformation gradient makes the model applicable to arbitrary plastic and damage deformations. To account for the physical mechanisms of failure, the concept of thermally activated damage initially proposed by Tuller and Bucher [3], Klepaczko [4] was adopted as the basis for the new damage evolution model. This makes the proposed damage/failure model compatible with the Mechanical Threshold Strength (MTS) model Follansbee and Kocks [5], 1988; Chen and Gray [6] which was used to control evolution of flow stress during plastic deformation. In

  16. On the localization of plastic strain under compression of LiF crystals

    Science.gov (United States)

    Barannikova, S. A.; Nadezhkin, M. V.; Zuev, L. B.

    2010-07-01

    The plastic flow localization patterns for alkali halide LiF crystals under compression have been investigated. The main spatiotemporal regularities of the strain localization at different stages of deformation hardening in the single crystals have been established. The relation has been traced between the orientation of localized strain zones and the crystallography of slip systems of the test specimens studied simultaneously by the double-exposure speckle photography and photoelasticity methods.

  17. Effect of strain rate and temperature at high strains on fatigue behavior of SAP alloys

    DEFF Research Database (Denmark)

    Blucher, J.T.; Knudsen, Per; Grant, N.J.

    1968-01-01

    Fatigue behavior of three SAP alloys of two nominal compositions (7 and 13% Al2O3) was studied in terms of strain rate and temperature at high strains; strain rate had no effect on life at 80 F, but had increasingly greater effect with increasing temperature above 500 F; life decreased with decre......Fatigue behavior of three SAP alloys of two nominal compositions (7 and 13% Al2O3) was studied in terms of strain rate and temperature at high strains; strain rate had no effect on life at 80 F, but had increasingly greater effect with increasing temperature above 500 F; life decreased...

  18. ON THE TENSILE MECHANICAL PROPERTY OF Si-Mn TRIP STEELS AT HIGH STRAIN RATE

    Institute of Scientific and Technical Information of China (English)

    X.C. Wei; L. Li; R.Y. Fu; W. Shi

    2002-01-01

    Tensile mechanical properties of 1.6Si-1.58Mn-0.195C TRIP (transformation-inducedplasticity) steels under high strain rate and effects of DP (dual-phase) treatments werestudied and compared to the quasi-static tensile behavior. The results show that theincreasing of strain rate leads to increasing in their strengths and decreasing in theuniform elongation remarkably. Because the stable retained austenite in TRIP steelcan transform to martensite during tensile testing and the material exhibits excellentcharacteristic of transformation induced plasticity, the plastic deformation behavior isevidently improved and the combination of strength and elongation is superior to thatof dual-phase steel, although its strength is smaller than that of DP steel. However,DP treated steel shown lower elongation under dynamic tension in spite of higherstrength. A model was proposed to explain the excellent elongation rate of TRIPsteel compared with DP steel on the basis of SEM analysis and the strength of thecomponents in microstructure.

  19. Myocardial Strain and Strain Rate Imaging: Comparison between Doppler Derived Strain Imaging and Speckle Tracking Echocardiography

    Directory of Open Access Journals (Sweden)

    Anita Sadeghpour

    2013-05-01

    Full Text Available Regional myocardial function has been traditionally assessed by visual estimation (1. Echocardiographic strain imaging which is known as deformation imaging, has been emerged as a quantitative technique to accurately estimate regional myocardial function and contractility. Currently, strain imaging has been regarded as a research tool in the most echocardiography laboratories. However, in recent years, strain imaging has gain momentum in daily clinical practice (2. The following two techniques have dominated the research arena of echocardiography: (1 Doppler based tissue velocity measurements, frequently referred to tissue Doppler or myocardial Doppler, and (2 speckle tracking on the basis of displacement measurements (3. Over the past two decades, Tissue Doppler Imaging (TDI and Doppler –derived strain (S and strain rate (SR imaging were introduced to quantify regional myocardial function. However, Doppler–derived strain variables faced criticisms, with regard to the angle dependency, noise interference, and substantial intraobserver and interobserver variability. The angle dependency is the major weakness of Doppler based methodology; however, it has the advantage of online measurements of velocities and time intervals with excellent temporal resolution, which is essential for the assessment of ischemia (4. Speckle-tracking echocardiography (STE or Non Doppler 2D strain echocardiography is a relatively new, largely angle-independent technique that analyzes motion by tracking natural acoustic reflections and interference patterns within an ultrasonic window. The image-processing algorithm tracks elements with approximately 20 to 40 pixels containing stable patterns and are described as ‘‘speckles’’ or ‘‘fingerprints’’. The speckles seen in grayscale B-mode (2D images are tracked consecutively frame to frame (5, 6. Assessment of 2D strain by STE is a semiautomatic method that requires definition of the myocardium

  20. High Strain, Strain Rate Behavior of PTFE/Al/W

    Science.gov (United States)

    Addiss, John; Cai, Jing; Walley, Steve; Proud, William; Nesterenko, Vitali

    2007-06-01

    Conventional dropweight technique was modified to accommodate low amplitude signals from low strength, cold isostatically pressed energetic ``heavy'' composites of polytetrafluoroethylene (PTFE)/AL/W. The fracture strength, strain and post-critical behaviour of fractured samples were measured for samples of different porosity and W grain size (the masses of each component being the same in each case). Unusual phenomenon of significantly higher strength (55 MPa) of porous composites (density 5.9 g/cc) with small tungsten particles (1 micron) in comparison with strength (32 MPa) of dense composites (7.1 g/cc) with larger tungsten particles (20 micron) was observed. This is attributed to force chains created by a network of small tungsten particles. Interrupted tests at the different level of strains revealed mechanism of fracture under dynamic compression.

  1. A deformation mechanism map for polycrystals modeled using strain gradient plasticity and interfaces that slide and separate

    DEFF Research Database (Denmark)

    Dahlberg, Carl F.O.; Faleskog, Jonas; Niordson, Christian Frithiof

    2013-01-01

    Small scale strain gradient plasticity is coupled with a model of grain boundaries that take into account the energetic state of a plastically strained boundary and the slip and separation between neighboring grains. A microstructure of hexagonal grains is investigated using a plane strain finite...... element model. The results show that three different microstructural deformation mechanisms can be identified. The standard plasticity case in which the material behaves as expected from coarse grained experiments, the nonlocal plasticity region where size of the microstructure compared to some intrinsic...

  2. Influence of cooling rate on cracking and plastic deformation during impact and indentation of borosilicate glasses.

    Science.gov (United States)

    Zehnder, Christoffer; Bruns, Sebastian; Peltzer, Jan-Niklas; Durst, Karsten; Korte-Kerzel, Sandra; Möncke, Doris

    2017-03-01

    The influence of a changing glass topology on local mechanical properties was studied in a multi-technique nanomechanical approach. The glass response against sharp contacts can result in structural densification, plastic flow or crack initiation. Using instrumented indentation testing, the mechanical response was studied in different strain rate regimes for a sodium-boro-silicate glass (NBS) exhibiting altering structures due to varying processing conditions. Comparison with data from former studies as well as with literature data on other glass structures helped to elucidate the role of the borate and silicate sub-networks and to understand the overall mechanical properties of the mixed glass systems. A peculiarity of some of the NBS glasses tested in this study is the fact that the connectivity of the borate and silicate entities depends on the sample’s thermal history. While the influence on macroscopic material properties such as E and H is minor, the onset of cracking indeed is influenced by those structural changes within the glass. Rapidly quenched glass shows an improved crack resistance, which is even more pronounced at high strain rates. Studies on various processing conditions further indicate that this transition is closely related to the cooling rate around Tg. The strain rate dependence of cracking is discussed in terms of the occurrence of shear deformation and densification.

  3. A Theory of Rate Coding Control by Intrinsic Plasticity Effects

    Science.gov (United States)

    Naudé, J.; Paz, J. T.; Berry, H.; Delord, B.

    2012-01-01

    Intrinsic plasticity (IP) is a ubiquitous activity-dependent process regulating neuronal excitability and a cellular correlate of behavioral learning and neuronal homeostasis. Because IP is induced rapidly and maintained long-term, it likely represents a major determinant of adaptive collective neuronal dynamics. However, assessing the exact impact of IP has remained elusive. Indeed, it is extremely difficult disentangling the complex non-linear interaction between IP effects, by which conductance changes alter neuronal activity, and IP rules, whereby activity modifies conductance via signaling pathways. Moreover, the two major IP effects on firing rate, threshold and gain modulation, remain unknown in their very mechanisms. Here, using extensive simulations and sensitivity analysis of Hodgkin-Huxley models, we show that threshold and gain modulation are accounted for by maximal conductance plasticity of conductance that situate in two separate domains of the parameter space corresponding to sub- and supra-threshold conductance (i.e. activating below or above the spike onset threshold potential). Analyzing equivalent integrate-and-fire models, we provide formal expressions of sensitivities relating to conductance parameters, unraveling unprecedented mechanisms governing IP effects. Our results generalize to the IP of other conductance parameters and allow strong inference for calcium-gated conductance, yielding a general picture that accounts for a large repertoire of experimental observations. The expressions we provide can be combined with IP rules in rate or spiking models, offering a general framework to systematically assess the computational consequences of IP of pharmacologically identified conductance with both fine grain description and mathematical tractability. We provide an example of such IP loop model addressing the important issue of the homeostatic regulation of spontaneous discharge. Because we do not formulate any assumptions on modification rules

  4. Three-dimensional frictional plastic strain partitioning during oblique rifting

    Science.gov (United States)

    Duclaux, Guillaume; Huismans, Ritske S.; May, Dave

    2017-04-01

    Throughout the Wilson cycle the obliquity between lithospheric plate motion direction and nascent or existing plate boundaries prompts the development of intricate three-dimensional tectonic systems. Where oblique divergence dominates, as in the vast majority of continental rift and incipient oceanic domains, deformation is typically transtensional and large stretching in the brittle upper crust is primarily achieved by the accumulation of displacement on fault networks of various complexity. In continental rift depressions such faults are initially distributed over tens to hundreds of kilometer-wide regions, which can ultimately stretch and evolve into passive margins. Here, we use high-resolution 3D thermo-mechanical finite element models to investigate the relative timing and distribution of localised frictional plastic deformation in the upper crust during oblique rift development in a simplified layered lithosphere. We vary the orientation of a wide oblique heterogeneous weak zone (representing a pre-existing geologic feature like a past orogenic domain), and test the sensitivity of the shear zones orientation to a range of noise distribution. These models allow us to assess the importance of material heterogeneities for controlling the spatio-temporal shear zones distribution in the upper crust during oblique rifting, and to discuss the underlying controls governing oblique continental breakup.

  5. A numerical investigation of grain shape and crystallographic texture effects on the plastic strain localization in friction stir weld zones

    Science.gov (United States)

    Romanova, V.; Balokhonov, R.; Batukhtina, E.; Shakhidjanov, V.

    2015-10-01

    Crystal plasticity approaches were adopted to build models accounting for the microstructure and texture observed in different friction stir weld zones. To this end, a numerical investigation of crystallographic texture and grain shape effects on the plastic strain localization in a friction stir weld of an aluminum-base alloy was performed. The presence of texture was found to give rise to pronounced mesoscale plastic strain localization.

  6. Dynamic tensile behaviour and deformational mechanism of C5191 phosphor bronze under high strain rates deformation

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Dao-chun [College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); College of Mechanical and Electrical Engineering, Taizhou Vocational & Technical College, Taizhou 318000 (China); Chen, Ming-he, E-mail: meemhchen@nuaa.edu.cn [College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Wang, Lei; Cheng, Hu [College of Mechanical Engineering, Taizhou University, Taizhou 318000 (China)

    2016-01-01

    High speed stamping process is used to high strength and high electrical conductivity phosphor bronze with extremely high strain rates more than 10{sup 3} s{sup −1}. This study on the dynamic tensile behaviour and deformational mechanism is to optimise the high speed stamping processes and improve geometrical precision in finished products. Thus, the tensile properties and deformation behaviour of C5191 phosphor bronze under quasi-static tensile condition at a strain rate of 0.001 s{sup −1} by electronic universal testing machine, and dynamic tensile condition at strain rate of 500, 1000 and 1500 s{sup −1} by split Hopkinson tensile bar (SHTB) apparatus were studied. The effects of strain rate and the deformation mechanism were investigated by means of SEM and TEM. The results showed that the yield strength and tensile strength of C5191 phosphor bronze under high strain rates deformation increased by 32.77% and 11.07% respectively compared with quasi-static condition, the strain hardening index increases from 0.075 to 0.251, and the strength of the material strain rates sensitivity index change from 0.005 to 0.022, which presented a clear sensitive to strain rates. Therefore, it is claimed that the dominant deformation mechanism was changed by the dislocation motion under different strain rates, and the ability of plastic deformation of C5191 phosphor bronze increased due to the number of movable dislocations increased significantly, started multi-line slip, and the soft effect of adiabatic temperature rise at the strain rate ranging from 500 to 1500 s{sup −1}.

  7. Engineering of surface microstructure transformations using high rate severe plastic deformation in machining

    Science.gov (United States)

    Abolghasem, Sepideh

    Engineering surface structures especially at the nanometer length-scales can enable fundamentally new multifunctional property combinations, including tunable physical, mechanical, electrochemical and biological responses. Emerging manufacturing paradigms involving Severe Plastic Deformation (SPD), for manipulating final microstructure of the surfaces are unfortunately limited by poorly elucidated process-structure-performance linkages, which are characterized by three central variables of plasticity: strain, strain-rate and temperature that determine the resulting Ultrafine Grained (UFG) microstructure. The challenge of UFG surface engineering, design and manufacturing can be overcome if and only if the mappings between the central variables and the final microstructure are delineated. The objective of the proposed document is to first envision a phase-space, whose axes are parameterized in terms of the central variables of SPD. Then, each point can correspond to a unique microstructure, characterized by its location on this map. If the parametrization and the population of the datasets are accurately defined, then the mapping is bijective where: i) realizing microstructure designs can be reduced to simply one of tuning process parameters falling within the map s desired subspaces. And, inversely, ii) microstructure prediction is directly possible by merely relating the measured/calculated thermomechanics at each point in the deformation zone to the corresponding spot on the maps. However, the analytic approach to establish this map first requires extensive datasets, where the microstructures are accurately measured for a known set of strain, strain-rate and temperature of applied SPD. Although such datasets do not exist, even after the empirical data is accumulated, there is a lack of formalized statistical outlines in relating microstructural characteristic to the process parameters in order to build the mapping framework. Addressing these gaps has led to this

  8. Uniaxial tension test on Rubber at constant true strain rate

    Directory of Open Access Journals (Sweden)

    Sourne H.L.

    2012-08-01

    Full Text Available Elastomers are widely used for damping parts in different industrial contexts because of their remarkable dissipation properties. Indeed, they can undergo severe mechanical loading conditions, i.e., high strain rates and large strains. Nevertheless, the mechanical response of these materials can vary from purely rubber-like to glassy depending on the strain rate undergone. Classically, uniaxial tension tests are made in order to find a relation between the stress and the strain in the material at various strain rates. However, even if the strain rate is searched to be constant, it is the nominal strain rate that is considered. Here we develop a test at constant true strain rate, i.e. the strain rate that is experienced by the material. In order to do such a test, the displacement imposed by the machine is an exponential function of time. This test has been performed with a high speed hydraulic machine for strain rates between 0.01/s and 100/s. A specific specimen has been designed, yielding a uniform strain field (and so a uniform stress field. Furthermore, an instrumented aluminum bar has been used to take into account dynamic effects in the measurement of the applied force. A high speed camera enables the determination of strain in the sample using point tracking technique. Using this method, the stress-strain curve of a rubber-like material during a loading-unloading cycle has been determined, up to a stretch ratio λ = 2.5. The influence of the true strain rate both on stiffness and on dissipation of the material is then discussed.

  9. The exponentiated Hencky-logarithmic strain energy: part III—coupling with idealized multiplicative isotropic finite strain plasticity

    Science.gov (United States)

    Neff, Patrizio; Ghiba, Ionel-Dumitrel

    2016-03-01

    We investigate an immediate application in finite strain multiplicative plasticity of the family of isotropic volumetric-isochoric decoupled strain energies F mapsto W_eH(F):= widehat{W}_eH(U) := μ/k e^{k | dev_n log {U}|^2}+κ/2 {widehat{k}} e^{widehat{k} [ tr(log U)]^2}&quad if& det F > 0, + ∞ & quad if & det F ≤ 0, based on the Hencky-logarithmic (true, natural) strain tensor {log U} . Here, {μ > 0} is the infinitesimal shear modulus, {κ=2 μ+3λ/3 > 0} is the infinitesimal bulk modulus with λ the first Lamé constant, {k,widehat{k}} are additional dimensionless material parameters, {F=nabla \\varphi} is the gradient of deformation, {U=√{F^T F}} is the right stretch tensor, and dev n {log {U} =log {U}-1/n tr(log {U})\\cdot{1}} is the deviatoric part of the strain tensor {log U} . Based on the multiplicative decomposition {F=F_e F_p} , we couple these energies with some isotropic elasto-plastic flow rules {F_p {dt}/[F_p^{-1}]in-partial χ(dev_3 Σe)} defined in the plastic distortion F p , where {partial χ} is the subdifferential of the indicator function {χ} of the convex elastic domain {E_e({Σe},1/3{σ}_{y}^2)} in the mixed-variant {Σe} -stress space, {Σe=F_e^T D_{F_e}W_iso(F_e)} , and {W_iso(F_e)} represents the isochoric part of the energy. While {W_eH} may loose ellipticity, we show that loss of ellipticity is effectively prevented by the coupling with plasticity, since the ellipticity domain of {W_eH} on the one hand and the elastic domain in {Σe} -stress space on the other hand are closely related. Thus, the new formulation remains elliptic in elastic unloading at any given plastic predeformation. In addition, in this domain, the true stress-true strain relation remains monotone, as observed in experiments.

  10. Effect of strain rate and temperature at high strains on fatigue behavior of SAP alloys

    DEFF Research Database (Denmark)

    Blucher, J.T.; Knudsen, Per; Grant, N.J.

    1968-01-01

    Fatigue behavior of three SAP alloys of two nominal compositions (7 and 13% Al2O3) was studied in terms of strain rate and temperature at high strains; strain rate had no effect on life at 80 F, but had increasingly greater effect with increasing temperature above 500 F; life decreased...

  11. In-situ strain localization analysis in low density transformation-twinning induced plasticity steel using digital image correlation

    Science.gov (United States)

    Eskandari, M.; Yadegari-Dehnavi, M. R.; Zarei-Hanzaki, A.; Mohtadi-Bonab, M. A.; Basu, R.; Szpunar, J. A.

    2015-04-01

    The effect of deformation temperature on the strain localization has been evaluated by an adapted digital image correlation (DIC) technique during tensile deformation. The progress of strain localization was traced by the corresponding strain maps. The electron backscatter diffraction analysis and tint etching technique were utilized to determine the impact of martensitic transformation and deformation twinning on the strain localization in both elastic and plastic regimes. In elastic regime the narrow strain bands which are aligned perpendicular to the tension direction were observed in temperature range of 25 to 180 °C due to the stress-assisted epsilon martensite. The strain bands were disappeared by increasing the temperature to 300 °C and reappeared at 400 °C due to the stress-assisted deformation twinning. In plastic regime strain localization continued at 25 °C and 180 °C due to the strain-induced alfa-martensite and deformation twinning, respectively. The intensity of plastic strain localization was increased by increasing the strain due to the enhancement of martensite and twin volume fraction. The plastic strain showed more homogeneity at 300 °C due to the lack of both strain-induced martensite and deformation twinning. Effect of deformation mechanism by changing temperature on strain localization is investigated by digital image correlation. EBSD technique is served to validate deformation mechanism as well as microstructural evolution. Strain induced martensite as well as deformation twinning is activated in the present steel affecting strain localization.

  12. Explicit mixed strain-displacement finite elements for compressible and quasi-incompressible elasticity and plasticity

    Science.gov (United States)

    Cervera, M.; Lafontaine, N.; Rossi, R.; Chiumenti, M.

    2016-09-01

    This paper presents an explicit mixed finite element formulation to address compressible and quasi-incompressible problems in elasticity and plasticity. This implies that the numerical solution only involves diagonal systems of equations. The formulation uses independent and equal interpolation of displacements and strains, stabilized by variational subscales. A displacement sub-scale is introduced in order to stabilize the mean-stress field. Compared to the standard irreducible formulation, the proposed mixed formulation yields improved strain and stress fields. The paper investigates the effect of this enhancement on the accuracy in problems involving strain softening and localization leading to failure, using low order finite elements with linear continuous strain and displacement fields ( P1 P1 triangles in 2D and tetrahedra in 3D) in conjunction with associative frictional Mohr-Coulomb and Drucker-Prager plastic models. The performance of the strain/displacement formulation under compressible and nearly incompressible deformation patterns is assessed and compared to analytical solutions for plane stress and plane strain situations. Benchmark numerical examples show the capacity of the mixed formulation to predict correctly failure mechanisms with localized patterns of strain, virtually free from any dependence of the mesh directional bias. No auxiliary crack tracking technique is necessary.

  13. Effects of strain rate on the mechanical properties of tricalcium phosphate/poly(L: -lactide) composites.

    Science.gov (United States)

    Yamadi, Shusaku; Kobayashi, Satoshi

    2009-01-01

    Bioactive ceramic/bioresorbable plastic composites have been expected as materials for the bone fracture fixations which have more biocompatibility than monolithic bioresorbable plastics. Many studies have been conducted on these materials. Most studies, however, focused on the mechanical properties under static loading. In the actual usage, these materials are loaded dynamically. In this study, effects of strain rate on the mechanical properties of tricalcium phosphate/poly(L: -lactide) (TCP/PLLA) composites were investigated experimentally and analytically. The TCP/PLLA composites containing three different TCP contents (5, 10 and 15 wt.%) were prepared by injection molding. In order to characterize the mechanical properties, tensile and compressive tests were conducted. The results of tensile tests indicated that the Young's moduli of composites increased with increasing TCP contents. For each TCP contents, tensile Young's modulus kept constant up to strain rate of 10(-1)/s. On the other hand, tensile strength increased with increasing strain rate. The effect of strain rate became larger with decreasing TCP contents, which means the strain rate dependency of the PLLA is more effective than that of TCP. From the results of compressive tests, similar results with tensile tests were obtained. That is, compressive Young's modulus kept constant up to strain rate of 10(-1)/s and the 0.2% proof stress increased with increasing strain rate. In order to predict the mechanical behavior of TCP/PLLA composites, the micro-damage mechanics was proposed. In this analysis, 3-phases particle reinforced composites, which include the intact particles, damaged particles and matrix, are assumed. The elastic constants are calculated with micromechanics based on the analyses by Eshelby and Mori and Tanaka. Only the debonding between particle and matrix are assumed as the damage. The nonlinearity in the stress-strain behavior of matrix PLLA is also considered. The debonding particles

  14. Tensile Properties of Fiber Materials under Different Strain Rates

    Institute of Scientific and Technical Information of China (English)

    XIONG Jie; GU Bo-hong; WANG Shan-yuan

    2002-01-01

    The quasi-static and dynamic tensile tests of aranid and high strength PVA fiber bundles are carried out under a wider range of strain rate by use of MTS (Materials Testing System) and bar-bar tensile impact apparatus.The influences of strain rate on mechanical properties of aramid and high strength polyvinyl alcohol fibers ar estudied. Micro failure mechanisms of fibers at different strain rates are examined by means of SEM.

  15. Strain rate effect in high-speed wire drawing process

    Science.gov (United States)

    He, S.; Van Houtte, P.; Van Bael, A.; Mei, F.; Sarban, A.; Boesman, P.; Galvez, F.; Atienza, J. M.

    2002-05-01

    This paper presents a study on the strain rate effect during high-speed wire drawing process by means of finite element simulation. Based on the quasistatic stresses obtained by normal tensile tests and dynamic stresses at high strain rates by split Hopkinson pressure bar tests, the wire drawing process was simulated for low carbon steel and high carbon steel. The results show that both the deformation process and the final properties of drawn wires are influenced by the strain rate.

  16. Inner-product of strain rate vector through direction cosine in coordinates for disk forging

    Institute of Scientific and Technical Information of China (English)

    ZHAO De-wen; JIN Wen-zhong; WANG Lei; LIU Xiang-hua

    2006-01-01

    A new linear integration for plastic power was proposed. The effective strain rate for disk forging with bulge was expressed in terms of two-dimensional strain rate vector, and then its direction cosines were determined by the ratio of coordinate increments. Furthermore, inner-product of the vector for plastic power was term integrated by term and summed. Thereafter, through a formula for determination of bulge an analytical solution of stress effective factor was obtained. Finally, through compression tests, the calculated results of above formula were compared with those of Avitzur's approximate solution and total indicator readings of the testing machine. It is indicated that the calculated compression forces are basically in agreement with the measured ones if the pass reduction is less than 13.35%.However, when the reduction gets up to 25.34% and 33.12%, the corresponding errors between the calculated and measured results also get up to 6% and 13.5%, respectively.

  17. Micromorphic approach for gradient-extended thermo-elastic-plastic solids in the logarithmic strain space

    Science.gov (United States)

    Aldakheel, Fadi

    2017-05-01

    The coupled thermo-mechanical strain gradient plasticity theory that accounts for microstructure-based size effects is outlined within this work. It extends the recent work of Miehe et al. (Comput Methods Appl Mech Eng 268:704-734, 2014) to account for thermal effects at finite strains. From the computational viewpoint, the finite element design of the coupled problem is not straightforward and requires additional strategies due to the difficulties near the elastic-plastic boundaries. To simplify the finite element formulation, we extend it toward the micromorphic approach to gradient thermo-plasticity model in the logarithmic strain space. The key point is the introduction of dual local-global field variables via a penalty method, where only the global fields are restricted by boundary conditions. Hence, the problem of restricting the gradient variable to the plastic domain is relaxed, which makes the formulation very attractive for finite element implementation as discussed in Forest (J Eng Mech 135:117-131, 2009) and Miehe et al. (Philos Trans R Soc A Math Phys Eng Sci 374:20150170, 2016).

  18. Theoretical and metrical standardization of strain rate sensitivity index

    Institute of Scientific and Technical Information of China (English)

    SONG; YuQuan; GUAN; ZhiPing; LI; ZhiGang; WANG; MingHui

    2007-01-01

    Strain rate sensitivity index m is one of the vital mechanical parameters for determining material superplasticity. In this paper, the existing formulae for measuring m value are reviewed, and it is found that the m values can be classified into three classes: mi under constant length, mv under constant velocity, and mp under constant load. The constraint equation of the generalized m value is established according to the tensile constitutive equation and the basis theory for plastic mechanics. Based on three typical deformation paths, the m value is redefined. Furthermore, from the formula of generalized m value, the formulae for measuring mi, mv and mp are theoretically deduced. The precise methods with numerical simulation are presented. The results prove that the m value is a non-constant and its dependence on (ε) changes with the deformation path. Under different deformation paths, the m values calculated from the same formula are different. Using different formulae, the m values under the same deformation path are also different. Therefore, deformation path and corresponding formula should be given during the measurement of the m value. Moreover, it is explained theoretically and experimentally that why the mv value under constant velocity is sometimes negative but the mp value under constant load is sometimes lager than 1. The aim of the analysis and measurement of the m value is to facilitate the study on the relationship between macroscopical mechanical laws and microscopic physical mechanisms during superplastic deformation.

  19. Study of creep behaviour in P-doped copper with slow strain rate tensile tests

    Energy Technology Data Exchange (ETDEWEB)

    Xuexing Yao; Sandstroem, Rolf [Royal Inst. of Tech., Stockholm (Sweden). Dept. of Materials Science and Engineering

    2000-08-01

    Pure copper with addition of phosphorous is planned to be used to construct the canisters for spent nuclear fuel. The copper canisters can be exposed to a creep deformation up to 2-4% at temperatures in services. The ordinary creep strain tests with dead weight loading are generally employed to study the creep behaviour; however, it is reported that an initial plastic deformation of 5-15% takes place when loading the creep specimens at lower temperatures. The slow strain rate tensile test is an alternative to study creep deformation behaviour of materials. Ordinary creep test and slow strain rate tensile test can give the same information in the secondary creep stage. The advantage of the tensile test is that the starting phase is much more controlled than in a creep test. In a tensile test the initial deformation behaviour can be determined and the initial strain of less than 5% can be modelled. In this study slow strain rate tensile tests at strain rate of 10{sup -4}, 10{sup -5}, 10{sup -6}, and 10{sup -7}/s at 75, 125 and 175 degrees C have been performed on P-doped pure Cu to supplement creep data from conventional creep tests. The deformation behaviour has successfully been modelled. It is shown that the slow strain rate tensile tests can be implemented to study the creep deformation behaviours of pure Cu.

  20. An Elastic Plastic Contact Model with Strain Hardening for the LAMMPS Granular Package

    Energy Technology Data Exchange (ETDEWEB)

    Kuhr, Bryan [Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States); Brake, Matthew Robert [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Component Science and Mechanics; Lechman, Jeremy B. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Nanoscale and Reactive Processes

    2015-03-01

    The following details the implementation of an analytical elastic plastic contact model with strain hardening for normal im pacts into the LAMMPS granular package. The model assumes that, upon impact, the co llision has a period of elastic loading followed by a period of mixed elastic plas tic loading, with contributions to each mechanism estimated by a hyperbolic seca nt weight function. This function is implemented in the LAMMPS source code as the pair style gran/ep/history. Preliminary tests, simulating the pouring of pure nickel spheres, showed the elastic/plastic model took 1.66x as long as similar runs using gran/hertz/history.

  1. Tensile plastic strain localization in single crystals of austenite steel electrolytically saturated with hydrogen

    Science.gov (United States)

    Barannikova, S. A.; Nadezhkin, M. V.; Mel'Nichuk, V. A.; Zuev, L. B.

    2011-09-01

    The effect of interstitial hydrogen atoms on the mechanical properties and plastic strain localization patterns in tensile tested Fe-18Cr-12Ni-2Mo single crystals of austenite steel with low stacking-fault energy has been studied using a double-exposure speckle photography technique. The main parameters of plastic-flow localization at various stages of the deformation hardening of crystals have been determined in single crystals of steel electrolytically saturated with hydrogen in a three-electrode electrochemical cell at a controlled constant cathode potential.

  2. Effect of hydrogen on plastic strain localization and fracture of steels

    Science.gov (United States)

    Nadjozhkin, M. V.; Lunev, A. G.; Li, Yu V.; Barannikova, S. A.

    2016-02-01

    The effect of interstitial hydrogen atoms on the mechanical properties and plastic strain localization patterns in tensile tested specimens of low-carbon steels have been studied using a double exposure speckle photography technique. It is found that the mechanical properties of low-carbon steels are affected adversely by hydrogen embrittlement. The deformation diagrams were examined for the deformed samples of low-carbon steels. These are found to show all the plastic flow stages: the linear, parabolic and pre-failure stages would occur for the respective values of the exponent n from the Ludwik-Holomon equation.

  3. Dynamic tensile testing for determining the stress-strain curve at different strain rate

    OpenAIRE

    Mansilla, A; Regidor, A.; García, D.; Negro, A

    2001-01-01

    A detailed discussion of high strain-rate tensile testing is presented. A comparative analysis of different ways to measure stress and strain is made. The experimental stress-strain curves have been suitably interpreted to distinguish between the real behaviour of the material and the influence of the testing methodology itself. A special two sections flat specimen design was performed through FEA computer modelling. The mechanical properties as function of strain rate were experimentally obt...

  4. Effects of gasket on coupled plastic flow and strain-induced phase transformations under high pressure and large torsion in a rotational diamond anvil cell

    Science.gov (United States)

    Feng, Biao; Levitas, Valery I.

    2016-01-01

    Combined plastic flow and strain-induced phase transformations (PTs) under high pressure in a sample within a gasket subjected to three dimensional compression and torsion in a rotational diamond anvil cell (RDAC) are studied using a finite element approach. The results are obtained for the weaker, equal-strength, and stronger high-pressure phases in comparison with low-pressure phases. It is found that, due to the strong gasket, the pressure in the sample is relatively homogenous and the geometry of the transformed zones is mostly determined by heterogeneity in plastic flow. For the equal-strength phases, the PT rate is higher than for the weaker and stronger high-pressure phases. For the weaker high-pressure phase, transformation softening induces material instability and leads to strain and PT localization. For the stronger high-pressure phase, the PT is suppressed by strain hardening during PT. The effect of the kinetic parameter k that scales the PT rate in the strain-controlled kinetic equation is also examined. In comparison with a traditional diamond anvil cell without torsion, the PT progress is much faster in RDAC under the same maximum pressure in the sample. Finally, the gasket size and strength effects are discussed. For a shorter and weaker gasket, faster plastic flow in radial and thickness directions leads to faster PT kinetics in comparison with a longer and stronger gasket. The rates of PT and plastic flows are not very sensitive to the modest change in a gasket thickness. Multiple experimental results are reproduced and interpreted. Obtained results allow one to design the desired pressure-plastic strain loading program in the experiments for searching new phases, reducing PT pressure by plastic shear, extracting kinetic properties from experiments with heterogeneous fields, and controlling homogeneity of all fields and kinetics of PTs.

  5. Identification of strain-rate and thermal sensitive material model with an inverse method

    Directory of Open Access Journals (Sweden)

    Peroni M.

    2010-06-01

    Full Text Available This paper describes a numerical inverse method to extract material strength parameters from the experimental data obtained via mechanical tests at different strainrates and temperatures. It will be shown that this procedure is particularly useful to analyse experimental results when the stress-strain fields in the specimen cannot be correctly described via analytical models. This commonly happens in specimens with no regular shape, in specimens with a regular shape when some instability phenomena occur (for example the necking phenomena in tensile tests that create a strongly heterogeneous stress-strain fields or in dynamic tests (where the strain-rate field is not constant due to wave propagation phenomena. Furthermore the developed procedure is useful to take into account thermal phenomena generally affecting high strain-rate tests due to the adiabatic overheating related to the conversion of plastic work. The method presented requires strong effort both from experimental and numerical point of view, anyway it allows to precisely identify the parameters of different material models. This could provide great advantages when high reliability of the material behaviour is necessary. Applicability of this method is particularly indicated for special applications in the field of aerospace engineering, ballistic, crashworthiness studies or particle accelerator technologies, where materials could be submitted to strong plastic deformations at high-strain rate in a wide range of temperature. Thermal softening effect has been investigated in a temperature range between 20°C and 1000°C.

  6. Towards ultra-high ductility TRIP-assisted multiphase steels controlled by strain gradient plasticity effects

    Science.gov (United States)

    Hatami, M. K.; Pardoen, T.; Lacroix, G.; Berke, P.; Jacques, P. J.; Massart, T. J.

    2017-01-01

    TRansformation Induced Plasticity (TRIP) is a very effective mechanism to increase the strain hardening capacity of multiphase steels containing a fraction of metastable austenite, leading to both high strength and large uniform elongation. Excellent performances have been reached in the past 20 years, with recent renewed interest through the development of the 3rd generation of high strength steels often involving a TRIP effect. The microstructure and composition optimization is complex due to the interplay of coupled effects on the transformation kinetics and work hardening such as phase stability, size of retained austenite grains, temperature and loading path. In particular, recent studies have shown that the TRIP effect can only be quantitatively captured for realistic microstructures if strain gradient plasticity effects are taken into account, although direct experimental validation of this claim is missing. Here, an original computational averaging scheme is developed for predicting the elastoplastic response of TRIP aided multiphase steels based on a strain gradient plasticity model. The microstructure is represented by an aggregate of many elementary unit cells involving each a fraction of retained austenite with a specified stability. The model parameters, involving the transformation kinetics, are identified based on experimental tensile tests performed at different temperatures. The model is further assessed towards original experiments, involving temperature changes during deformation. A classical size independent plasticity model is shown unable to capture the TRIP effect on the mechanical response. Conversely, the strain gradient formulation properly predicts substantial variations of the strain hardening with deformation and temperature, hence of the uniform elongation in good agreement with the experiments. A parametric study is performed to get more insight on the effect of the material length scale as well as to determine optimum transformation

  7. Strain Rate Effects in CFRP Used For Blast Mitigation

    Directory of Open Access Journals (Sweden)

    Sarah. L. Orton

    2014-04-01

    Full Text Available The purpose of this research is to gain a better understanding of strain rate effects in carbon fiber reinforced polymer (CFRP laminates exposed to blast loading. The use of CFRP offers an attractive option for mitigating structures exposed to blasts. However, the effect of high strain rates in CFRP composites commonly used in the civil industry is unknown. This research conducted tensile tests of 21 CFRP coupons using a hydraulically powered dynamic loader. The strain rates ranged from 0.0015 s−1 to 7.86 s−1 and are representative of strain rates that CFRP may see in a blast when used to strengthen reinforced concrete structures. The results of the testing showed no increase in the tensile strength or stiffness of the CFRP at the higher strain rates. In addition, the results showed significant scatter in the tensile strengths possibly due to the rate of loading or manufacture of the coupon.

  8. High Strain Rate Compressive Tests on Woven Graphite Epoxy Composites

    Science.gov (United States)

    Allazadeh, Mohammad Reza; Wosu, Sylvanus N.

    2011-08-01

    The behavior of composite materials may be different when they are subjected to high strain rate load. Penetrating split Hopkinson pressure bar (P-SHPB) is a method to impose high strain rate on specimen in the laboratory experiments. This research work studied the response of the thin circular shape specimens, made out of woven graphite epoxy composites, to high strain rate impact load. The stress-strain relationships and behavior of the specimens were investigated during the compressive dynamic tests for strain rates as high as 3200 s-1. One dimensional analysis was deployed for analytical calculations since the experiments fulfilled the ratio of diameter to length of bars condition in impact load experiments. The mechanics of dynamic failure was studied and the results showed the factors which govern the failure mode in high strain deformation via absorbed energy by the specimen. In this paper, the relation of particle velocity with perforation depth was discussed for woven graphite epoxy specimens.

  9. The effect of strain rate on the evolution of microstructure in aluminium alloys.

    Science.gov (United States)

    Leszczyńska-Madej, B; Richert, M

    2010-03-01

    Intensive deformations influence strongly microstructure. The very well-known phenomenon is the diminishing dimension of grain size by the severe plastic deformation (SPD) methods. The nanometric features of microstructure were discovered after the SPD deformation of various materials, such as aluminium alloys, iron and others. The observed changes depended on the kind of the deformed material, amount of deformation, strain rate, existence of different phases and stacking fault energy. The influence of the strain and strain rate on the microstructure is commonly investigated nowadays. It was found that the high strain rates activate deformation in shear bands, microbands and adiabatic shear bands. It was observed that bands were places of the nucleation of nanograins in the material deformed by SPD methods. In the work, the refinement of microstructure of the aluminium alloys influenced by the high strain rate was investigated. The samples were compressed by a specially designed hammer to the deformation of phi= 0/0.62 with the strain rate in the range of [Formula in text]. The highest reduction of microbands width with the increase of the strain was found in the AlCu4Zr alloy. The influence of the strain rate on the microstructure refinement indicated that the increase of the strain rate caused the reduction of the microbands width in the all investigated materials (Al99.5, AlCu4Zr, AlMg5, AlZn6Mg2.5CuZr). A characteristic feature of the microstructure of the compressed material was large density of the shear bands and microbands. It was found that the microbands show a large misorientation to the surrounds and, except Al99.5, the large density of dislocation.

  10. Determination of the strain rate dependent thermal softening behavior of thermoplastic materials for crash simulations

    Science.gov (United States)

    Hopmann, Christian; Klein, Jan; Schöngart, Maximilian

    2016-03-01

    Thermoplastic materials are increasingly used as a light weight replacement for metal, especially in automotive applications. Typical examples are frontends and bumpers. The loads on these structures are very often impulsive, for example in a crash situation. A high rate of loading causes a high strain rate in the material which has a major impact on the mechanical behavior of thermoplastic materials. The stiffness as well as the rigidity of polymers increases to higher strain rates. The increase of the mechanical properties is superimposed at higher rates of loading by another effect which works reducing on stiffness and rigidity, the increase of temperature caused by plastic deformation. The mechanical behavior of thermoplastic materials is influenced by temperature opposing to strain rate. The stiffness and rigidity are decreased to higher values of temperature. The effect of thermal softening on thermoplastic materials is investigated at IKV. For this purpose high-speed tensile tests are performed on a blend, consisting of Polybutylenterephthalate (PBT) and Polycarbonate (PC). In preliminary investigations the effects of strain rate on the thermomechanical behavior of thermoplastic materials was studied by different authors. Tensile impact as well as split Hopkinson pressure bar (SHPB) tests were conducted in combination with high-speed temperature measurement, though, the authors struggled especially with temperature measurement. This paper presents an approach which uses high-speed strain measurement to transpire the link between strain, strain rate and thermal softening as well as the interdependency between strain hardening and thermal softening. The results show a superimposition of strain hardening and thermal softening, which is consistent to preliminary investigations. The advantage of the presented research is that the results can be used to calibrate damage and material models to perform mechanical simulations using Finite Element Analysis.

  11. Characterization of a New Fully Recycled Carbon Fiber Reinforced Composite Subjected to High Strain Rate Tension

    Science.gov (United States)

    Meftah, H.; Tamboura, S.; Fitoussi, J.; BenDaly, H.; Tcharkhtchi, A.

    2017-08-01

    The aim of this study is the complete physicochemical characterization and strain rate effect multi-scale analysis of a new fully recycled carbon fiber reinforced composites for automotive crash application. Two composites made of 20% wt short recycled carbon fibers (CF) are obtained by injection molding. The morphology and the degree of dispersion of CF in the matrixes were examined using a new ultrasonic method and SEM. High strain tensile behavior up to 100 s-1 is investigated. In order to avoid perturbation due to inertial effect and wave propagation, the specimen geometry was optimized. The elastic properties appear to be insensitive to the strain rate. However, a high strain rate effect on the local visco-plasticity of the matrix and fiber/matrix interface visco-damageable behavior is emphasized. The predominant damage mechanisms evolve from generalized matrix local ductility at low strain rate regime to fiber/matrix interface debonding and fibers pull-out at high strain rate regime.

  12. Strain localization band width evolution by electronic speckle pattern interferometry strain rate measurement

    Energy Technology Data Exchange (ETDEWEB)

    Guelorget, Bruno [Institut Charles Delaunay-LASMIS, Universite de technologie de Troyes, FRE CNRS 2848, 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France)], E-mail: bruno.guelorget@utt.fr; Francois, Manuel; Montay, Guillaume [Institut Charles Delaunay-LASMIS, Universite de technologie de Troyes, FRE CNRS 2848, 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France)

    2009-04-15

    In this paper, electronic speckle pattern interferometry strain rate measurements are used to quantify the width of the strain localization band, which occurs when a sheet specimen is submitted to tension. It is shown that the width of this band decreases with increasing strain. Just before fracture, this measured width is about five times wider than the shear band and the initial sheet thickness.

  13. Elastic-Plastic Strain Acceptance Criteria for Structures Subject to Rapidly Applied Transient Dynamic Loading

    Energy Technology Data Exchange (ETDEWEB)

    W.R. Solonick

    2003-04-01

    Rapidly applied transient dynamic loads produce stresses and deflections in structures that typically exceed those from static loading conditions. Previous acceptance criteria for structures designed for rapidly applied transient dynamic loading limited stresses to those determined from elastic analysis. Different stress limits were established for different grades of structure depending upon the amount of permanent set considered acceptable. Structure allowed to sustain very limited permanent set is designed to stress limits not significantly greater than yield stress. Greater permanent set in structure under rapidly applied transient dynamic loading conditions is permitted by establishing stress limits that are significantly greater than yield stress but still provide adequate safety margin (with respect to failure). This paper presents a strain-based elastic-plastic (i.e., inelastic) analysis criterion developed as an alternative to the more conservative stress-based elastic analysis stress criterion for structures subjected to rapidly applied transient dynamic loading. The strain limits established are based on material ductility considerations only and are set as a fraction of the strain at ultimate stress obtained from an engineering stress/strain curve of the material. Strains limits are categorized by type as membrane or surface and by region as general, local , or concentrated. The application of the elastic-plastic criterion provides a more accurate, less conservative design/analysis basis for structures than that used in elastic stress-based analysis criteria, while still providing adequate safety margins.

  14. Combined grain size, strain rate and loading condition effects on mechanical behavior of nanocrystalline Cu under high strain rates

    Institute of Scientific and Technical Information of China (English)

    Lu-Ming Shen

    2012-01-01

    Molecular dynamics simulations of nanocrystalline Cu with average grain sizes of 3.1 nm,6.2 nm,12.4 nm and 18.6 nm under uniaxial strain and stress tension at strain rates of 108 s-1,109 s-1 and 1010 s-1 are performed to study the combined grain size,strain rate and loading condition effects on mechanical properties. It is found that the strength of nanocrystalline Cu increases as grain size increases regardless of loading condition.Both the strength and ductility of nanocrystalline Cu increase with strain rate except that there is no monotonic relation between the strength and strain rate for specimens under uniaxial strain loading.Moreover,the strength and ductility of specimens under uniaxial strain loading are lower than those under uniaxial stress loading.The nucleation of voids at grain boundaries and their subsequent growth characterize the failure of specimens under uniaxial strain loading,while grain boundary sliding and necking dominate the failure of specimens under uniaxial stress loading.The rate dependent strength is mainly caused by the dynamic wave effect that limits dislocation motion,while combined twinning and slipping mechanism makes the material more ductile at higher strain rates.

  15. Micro-Structural Evolution and Size-Effects in Plastically Deformed Single Crystals: Strain Gradient Continuum Modeling

    DEFF Research Database (Denmark)

    El-Naaman, Salim Abdallah

    , to focus on their ability to capture realistic micro-structural evolution. This challenge is the main focus of the present thesis, which takes as starting point a non-work conjugate type back stress based higher order crystal plasticity theory. Within this framework, several possibilities for the back......An extensive amount of research has been devoted to the development of micro-mechanics based gradient plasticity continuum theories, which are necessary for modeling micron-scale plasticity when large spatial gradients of plastic strain appear. While many models have proven successful in capturing...... the macroscopic effects related to strain gradients, most predict smooth micro-structures. The evolution of dislocation micro-structures, during plastic straining of ductile crystalline materials, is highly complex and nonuniform. Published experimental measurements on deformed metal crystals show distinct...

  16. Activated dynamic strain aging of a TRIP590 Steel at 300 °C and low strain rate and relationship to structure

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Y.F., E-mail: shenyf@smm.neu.edu.cn [Key Laboratory for Anisotropy and Texture of Materials (MOE), Northeastern University, Shenyang 110004 (China); Wang, P.J.; Liu, Y.D. [Key Laboratory for Anisotropy and Texture of Materials (MOE), Northeastern University, Shenyang 110004 (China); Misra, R.D.K., E-mail: dmisra2@utep.edu [Laboratory for Excellence in Advanced Steel Research, Department of Metallurgical and Materials Engineering, University of Texas at El Paso, TX 79968 (United States); Zuo, L. [Key Laboratory for Anisotropy and Texture of Materials (MOE), Northeastern University, Shenyang 110004 (China)

    2015-10-01

    Transformation-induced plasticity (TRIP) steel was subjected to intercritical annealing and bainite partitioning to elucidate the impact on mechanical properties at temperatures in the range of −70 °C to 300 °C and strain rates of 10{sup −3} to 10{sup −1} s{sup −1} and the behavior related to structure. At temperatures in the range of −70 °C to 150 °C, both the yield strength and tensile strength increased with decrease in the deformation temperature at a constant strain rate. The elongation-to-failure was maximum at room temperature, while the product of strength and ductility was highest at the lowest temperature of −70 °C at various strain rates. Unexpectedly, the serrated flow was observed for specimens tested at 300 °C, which is attributed to dynamic strain aging (DSA), an effect that became more pronounced with decrease in strain rate. The nanosized precipitates facilitated increase in dislocation density during plastic deformation by restraining recovery and annihilation of dislocations, leading to increase in stress with increase in temperature, an effect that decreased with increase in strain rate because of adiabatic heating.

  17. On the influence of strain rate sensitivity on wear in the Archard regime

    Energy Technology Data Exchange (ETDEWEB)

    Brechet, Y. (Domaine Univ. de Grenoble, Saint Martin d' Heres (France). Lab. de Thermodynamique et Physico-Chimie Metallurgique); Estrin, Y. (Univ. of Western Australia, Nedlands (Australia). Dept. of Mechanical and Materials Engineering)

    1994-06-01

    Relating wear characteristics of a metallic material to its mechanical properties (yield strength, strain hardening coefficient) and its microstructural features (size and volume fraction of inclusions) is a long-standing problem. The diversity of mechanisms which are involved during wear processes makes it practically impossible to have a general theory which would encompass all thinkable situations corresponding to various loads and various regimes of sliding. Different regimes and the conditions for their occurrence have been systematized in wear mechanism maps. In this communication the authors are going to restrict their consideration to plasticity dominated wear which is expected to occur in the low velocity range where surface heating is negligible. In this regime, the prevalent wear mechanism is the removal of slivers of metal by plastic failure due to shearing of contact asperities. The classic works by Rabinowicz have demonstrated clearly that solid friction is a rate dependent problem and that the velocity dependence of dynamic solid friction is nothing else than a consequence of the increase of static solid friction with time during which normal load was applied prior to the commencement of sliding. Creep under normal compression stress leads to flattening of the junctions causing their strength to increase with time. Like solid friction, wear appears to be a rate dependent phenomenon, and the strain rate sensitivity of the flow stress can be expected to be relevant for wear resistance. The strain rate sensitivity is known to play an important role in other damage related properties, such as ductility and fracture toughness. The authors felt that it would be of interest to evaluate the effect of strain rate sensitivity on the wear rate as part of an attempt to relate the wear properties to a bulk constitutive equation, and as a guideline for assessing the influence of alloying elements known to affect the strain rate sensitivity.

  18. Strain rate measurement by Electronic Speckle Pattern Interferometry: A new look at the strain localization onset

    Energy Technology Data Exchange (ETDEWEB)

    Guelorget, Bruno [Universite de Technologie de Troyes (UTT), Laboratoire des Systemes Mecaniques et d' ingenierie Simultanee (LASMIS, CNRS FRE 2719), 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France)]. E-mail: bruno.guelorget@utt.fr; Francois, Manuel [Universite de Technologie de Troyes (UTT), Laboratoire des Systemes Mecaniques et d' ingenierie Simultanee (LASMIS, CNRS FRE 2719), 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France); Vial-Edwards, Cristian [Departemento de Ingenieria Mecanica y Metalurgica, Pontificia Universidad Catolica de Chile, Vicuna Mackenna 4860, 6904411 Santiago (Chile); Montay, Guillaume [Universite de Technologie de Troyes (UTT), Laboratoire des Systemes Mecaniques et d' ingenierie Simultanee (LASMIS, CNRS FRE 2719), 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France); Daniel, Laurent [Universite de Technologie de Troyes (UTT), Laboratoire des Systemes Mecaniques et d' ingenierie Simultanee (LASMIS, CNRS FRE 2719), 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France); Lu, Jian [Universite de Technologie de Troyes (UTT), Laboratoire des Systemes Mecaniques et d' ingenierie Simultanee (LASMIS, CNRS FRE 2719), 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France)

    2006-01-15

    In-plane Electronic Speckle Pattern Interferometry has been successfully used during tensile testing of semi-hard copper sheets in order to measure the strain rate. On one hand, heterogeneity in strain rate field has been found before the maximum of the tensile force ({epsilon} {sup t} {approx_equal} 19.4 and 25.4%, respectively). Thus, a localization phenomenon occurs before the classic Considere's criterion (dF = 0) for the diffuse neck initiation. On the other hand, strain rate measurement before fracture shows the moment where one of the two slip band systems becomes predominant, then strain concentrates in a small area, the shear band. Uncertainty evaluation has been carried out, which shows a very good accuracy of the total strain and the strain rate measurements.

  19. Material dynamics under extreme conditions of pressure and strain rate

    Energy Technology Data Exchange (ETDEWEB)

    Remington, B A; Allen, P; Bringa, E; Hawreliak, J; Ho, D; Lorenz, K T; Lorenzana, H; Meyers, M A; Pollaine, S W; Rosolankova, K; Sadik, B; Schneider, M S; Swift, D; Wark, J; Yaakobi, B

    2005-09-06

    Solid state experiments at extreme pressures (10-100 GPa) and strain rates ({approx}10{sup 6}-10{sup 8}s{sup -1}) are being developed on high-energy laser facilities, and offer the possibility for exploring new regimes of materials science. These extreme solid-state conditions can be accessed with either shock loading or with a quasi-isentropic ramped pressure drive. Velocity interferometer measurements establish the high pressure conditions. Constitutive models for solid-state strength under these conditions are tested by comparing 2D continuum simulations with experiments measuring perturbation growth due to the Rayleigh-Taylor instability in solid-state samples. Lattice compression, phase, and temperature are deduced from extended x-ray absorption fine structure (EXAFS) measurements, from which the shock-induced {alpha}-{omega} phase transition in Ti and the {alpha}-{var_epsilon} phase transition in Fe are inferred to occur on sub-nanosec time scales. Time resolved lattice response and phase can also be measured with dynamic x-ray diffraction measurements, where the elastic-plastic (1D-3D) lattice relaxation in shocked Cu is shown to occur promptly (< 1 ns). Subsequent large-scale molecular dynamics (MD) simulations elucidate the microscopic dynamics that underlie the 3D lattice relaxation. Deformation mechanisms are identified by examining the residual microstructure in recovered samples. The slip-twinning threshold in single-crystal Cu shocked along the [001] direction is shown to occur at shock strengths of {approx}20 GPa, whereas the corresponding transition for Cu shocked along the [134] direction occurs at higher shock strengths. This slip-twinning threshold also depends on the stacking fault energy (SFE), being lower for low SFE materials. Designs have been developed for achieving much higher pressures, P > 1000 GPa, in the solid state on the National Ignition Facility (NIF) laser.

  20. Twinning in copper deformed at high strain rates

    Indian Academy of Sciences (India)

    S Cronje; R E Kroon; W D Roos; J H Neethling

    2013-02-01

    Copper samples having varying microstructures were deformed at high strain rates using a split-Hopkinson pressure bar. Transmission electron microscopy results show deformation twins present in samples that were both annealed and strained, whereas samples that were annealed and left unstrained, as well as samples that were unannealed and strained, are devoid of these twins. These deformation twins occurred at deformation conditions less extreme than previously predicted.

  1. Study of High Strain Rate Response of Composites

    Science.gov (United States)

    Gilat, Amos

    2003-01-01

    The objective of the research was to continue the experimental study of the effect of strain rate on mechanical response (deformation and failure) of epoxy resins and carbon fibers/epoxy matrix composites, and to initiate a study of the effects of temperature by developing an elevated temperature test. The experimental data provide the information needed for NASA scientists for the development of a nonlinear, rate dependent deformation and strength models for composites that can subsequently be used in design. This year effort was directed into testing the epoxy resin. Three types of epoxy resins were tested in tension and shear at various strain rates that ranges from 5 x 10(exp -5), to 1000 per second. Pilot shear experiments were done at high strain rate and an elevated temperature of 80 C. The results show that all, the strain rate, the mode of loading, and temperature significantly affect the response of epoxy.

  2. Effects of temperature and strain rate on the tensile properties of potassium-doped tungsten

    Energy Technology Data Exchange (ETDEWEB)

    Sasaki, Kenta, E-mail: k.sasaki@jupiter.qse.tohoku.ac.jp; Yabuuchi, Kiyohiro, E-mail: kiyohiro.yabuuchi@qse.tohoku.ac.jp; Nogami, Shuhei, E-mail: shuhei.nogami@qse.tohoku.ac.jp; Hasegawa, Akira, E-mail: akira.hasegawa@qse.tohoku.ac.jp

    2015-06-15

    Tensile tests were performed on pure and K-doped tungsten at temperatures from 25 to 700 °C and strain rates between 10{sup −5} and 10{sup −1} s{sup −1} in vacuum. The yield strength of both materials increased with increasing strain rate and decreasing temperature. The amount of change in the yield strength decreased with increasing temperature. The determination of activation volumes for plastic deformation highlighted that the rate-controlling process of the deformation behavior at lower temperatures was the same for both materials, namely, kink-pair formation on screw dislocations, and the process was not affected by potassium addition. The fracture strain of both materials increased with increasing strain rate and decreasing temperature, in the temperature range where the materials showed measurable ductility. K-doped W showed higher yield strength and a lower ductile-to-brittle transition temperature than pure W. No negative effect of K addition on strain rate- and temperature-induced changes in tensile properties was found. The analysis also highlighted the effectiveness of K addition, and of the grain refinement induced by it, for improving the mechanical properties of tungsten.

  3. Effects of temperature and strain rate on the tensile properties of potassium-doped tungsten

    Science.gov (United States)

    Sasaki, Kenta; Yabuuchi, Kiyohiro; Nogami, Shuhei; Hasegawa, Akira

    2015-06-01

    Tensile tests were performed on pure and K-doped tungsten at temperatures from 25 to 700 °C and strain rates between 10-5 and 10-1 s-1 in vacuum. The yield strength of both materials increased with increasing strain rate and decreasing temperature. The amount of change in the yield strength decreased with increasing temperature. The determination of activation volumes for plastic deformation highlighted that the rate-controlling process of the deformation behavior at lower temperatures was the same for both materials, namely, kink-pair formation on screw dislocations, and the process was not affected by potassium addition. The fracture strain of both materials increased with increasing strain rate and decreasing temperature, in the temperature range where the materials showed measurable ductility. K-doped W showed higher yield strength and a lower ductile-to-brittle transition temperature than pure W. No negative effect of K addition on strain rate- and temperature-induced changes in tensile properties was found. The analysis also highlighted the effectiveness of K addition, and of the grain refinement induced by it, for improving the mechanical properties of tungsten.

  4. Strain gradient crystal plasticity analysis of a single crystal containing a cylindrical void

    DEFF Research Database (Denmark)

    Borg, Ulrik; Kysar, J.W.

    2007-01-01

    The effects of void size and hardening in a hexagonal close-packed single crystal containing a cylindrical void loaded by a far-field equibiaxial tensile stress under plane strain conditions are studied. The crystal has three in-plane slip systems oriented at the angle 60 degrees with respect...... to one another. Finite element simulations are performed using a strain gradient crystal plasticity formulation with an intrinsic length scale parameter in a non-local strain gradient constitutive framework. For a vanishing length scale parameter the non-local formulation reduces to a local crystal...... to three times higher for smaller void sizes than for larger void sizes in the non-local material....

  5. Elastocaloric cooling processes: The influence of material strain and strain rate on efficiency and temperature span

    Science.gov (United States)

    Schmidt, Marvin; Schütze, Andreas; Seelecke, Stefan

    2016-06-01

    This paper discusses the influence of material strain and strain rate on efficiency and temperature span of elastocaloric cooling processes. The elastocaloric material, a newly developed quaternary Ni-Ti-Cu-V alloy, is characterized at different maximum strains and strain rates. The experiments are performed with a specially designed test setup, which enables the measurement of mechanical and thermal process parameters. The material efficiency is compared to the efficiency of the Carnot process at equivalent thermal operation conditions. This method allows for a direct comparison of the investigated material with other caloric materials.

  6. Elastocaloric cooling processes: The influence of material strain and strain rate on efficiency and temperature span

    Directory of Open Access Journals (Sweden)

    Marvin Schmidt

    2016-06-01

    Full Text Available This paper discusses the influence of material strain and strain rate on efficiency and temperature span of elastocaloric cooling processes. The elastocaloric material, a newly developed quaternary Ni-Ti-Cu-V alloy, is characterized at different maximum strains and strain rates. The experiments are performed with a specially designed test setup, which enables the measurement of mechanical and thermal process parameters. The material efficiency is compared to the efficiency of the Carnot process at equivalent thermal operation conditions. This method allows for a direct comparison of the investigated material with other caloric materials.

  7. Strain Rate Dependent Modeling of Polymer Matrix Composites

    Science.gov (United States)

    Goldberg, Robert K.; Stouffer, Donald C.

    1999-01-01

    A research program is in progress to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. Strain rate dependent inelastic constitutive equations have been developed to model the polymer matrix, and have been incorporated into a micromechanics approach to analyze polymer matrix composites. The Hashin failure criterion has been implemented within the micromechanics results to predict ply failure strengths. The deformation model has been implemented within LS-DYNA, a commercially available transient dynamic finite element code. The deformation response and ply failure stresses for the representative polymer matrix composite AS4/PEEK have been predicted for a variety of fiber orientations and strain rates. The predicted results compare favorably to experimentally obtained values.

  8. Stretching Behavior of Red Blood Cells at High Strain Rates

    Science.gov (United States)

    Mancuso, Jordan; Ristenpart, William

    2016-11-01

    Most work on the mechanical behavior of red blood cells (RBCs) has focused on simple shear flows. Relatively little work has examined RBC deformations in the physiologically important extensional flow that occurs at the entrance to a constriction. In particular, previous work suggests that RBCs rapidly stretch out and then retract upon entering the constriction, but to date no model predicts this behavior for the extremely high strain rates typically experienced there. In this work, we use high speed video to perform systematic measurements of the dynamic stretching behavior of RBCs as they enter a microfluidic constriction. We demonstrate that a simple viscoelastic model captures the observed stretching dynamics, up to strain rates as high as 1000 s-1. The results indicate that the effective elastic modulus of the RBC membrane at these strain rates is an order of magnitude larger than moduli measured by micropipette aspiration or other low strain rate techniques.

  9. Behaviour and modelling of aluminium alloy AA6060 subjected to a wide range of strain rates and temperatures

    Directory of Open Access Journals (Sweden)

    Vilamosa Vincent

    2015-01-01

    Full Text Available The thermo-mechanical behaviour in tension of an as-cast and homogenized AA6060 alloy was investigated at a wide range of strains (the entire deformation process up to fracture, strain rates (0.01–750 s−1 and temperatures (20–350 ∘C. The tests at strain rates up to 1 s−1 were performed in a universal testing machine, while a split-Hopkinson tension bar (SHTB system was used for strain rates from 350 to 750 s−1. The samples were heated with an induction-based heating system. A typical feature of aluminium alloys at high temperatures is that necking occurs at a rather early stage of the deformation process. In order to determine the true stress-strain curve also after the onset of necking, all tests were instrumented with a digital camera. The experimental tests reveal that the AA6060 material has negligible strain-rate sensitivity (SRS for temperatures lower than 200 ∘C, while both yielding and work hardening exhibit a strong positive SRS at higher temperatures. The coupled strain-rate and temperature sensitivity is challenging to capture with most existing constitutive models. The paper presents an outline of a new semi-physical model that expresses the flow stress in terms of plastic strain, plastic strain rate and temperature. The parameters of the model were determined from the tests, and the stress-strain curves from the tests were compared with the predictions of the model. Good agreement was obtained over the entire strain rate and temperature range.

  10. A High-Rate, Single-Crystal Model including Phase Transformations, Plastic Slip, and Twinning

    Energy Technology Data Exchange (ETDEWEB)

    Addessio, Francis L. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Theoretical Division; Bronkhorst, Curt Allan [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Theoretical Division; Bolme, Cynthia Anne [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Explosive Science and Shock Physics Division; Brown, Donald William [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Materials Science and Technology Division; Cerreta, Ellen Kathleen [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Materials Science and Technology Division; Lebensohn, Ricardo A. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Materials Science and Technology Division; Lookman, Turab [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Theoretical Division; Luscher, Darby Jon [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Theoretical Division; Mayeur, Jason Rhea [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Theoretical Division; Morrow, Benjamin M. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Materials Science and Technology Division; Rigg, Paulo A. [Washington State Univ., Pullman, WA (United States). Dept. of Physics. Inst. for Shock Physics

    2016-08-09

    An anisotropic, rate-­dependent, single-­crystal approach for modeling materials under the conditions of high strain rates and pressures is provided. The model includes the effects of large deformations, nonlinear elasticity, phase transformations, and plastic slip and twinning. It is envisioned that the model may be used to examine these coupled effects on the local deformation of materials that are subjected to ballistic impact or explosive loading. The model is formulated using a multiplicative decomposition of the deformation gradient. A plate impact experiment on a multi-­crystal sample of titanium was conducted. The particle velocities at the back surface of three crystal orientations relative to the direction of impact were measured. Molecular dynamics simulations were conducted to investigate the details of the high-­rate deformation and pursue issues related to the phase transformation for titanium. Simulations using the single crystal model were conducted and compared to the high-­rate experimental data for the impact loaded single crystals. The model was found to capture the features of the experiments.

  11. Multi-scale Modeling of the Impact Response of a Strain Rate Sensitive High-Manganese Austenitic Steel

    Directory of Open Access Journals (Sweden)

    Orkun eÖnal

    2014-09-01

    Full Text Available A multi-scale modeling approach was applied to predict the impact response of a strain rate sensitive high-manganese austenitic steel. The roles of texture, geometry and strain rate sensitivity were successfully taken into account all at once by coupling crystal plasticity and finite element (FE analysis. Specifically, crystal plasticity was utilized to obtain the multi-axial flow rule at different strain rates based on the experimental deformation response under uniaxial tensile loading. The equivalent stress – equivalent strain response was then incorporated into the FE model for the sake of a more representative hardening rule under impact loading. The current results demonstrate that reliable predictions can be obtained by proper coupling of crystal plasticity and FE analysis even if the experimental flow rule of the material is acquired under uniaxial loading and at moderate strain rates that are significantly slower than those attained during impact loading. Furthermore, the current findings also demonstrate the need for an experiment-based multi-scale modeling approach for the sake of reliable predictions of the impact response.

  12. High strain rate compression testing of glass fibre reinforced polypropylene

    Directory of Open Access Journals (Sweden)

    Cloete T.J.

    2012-08-01

    Full Text Available This paper details an investigation of the high strain rate compression testing of GFPP with the Split Hopkinson Pressure Bar (SHPB in the through-thickness and in-plane directions. GFPP posed challenges to SHPB testing as it fails at relatively high stresses, while having relatively low moduli and hence mechanical impedance. The modifications to specimen geometry and incident pulse shaping in order to gather valid test results, where specimen equilibrium was achieved for SHPB tests on GFPP are presented. In addition to conventional SHPB tests to failure, SHPB experiments were designed to achieve specimen equilibration at small strains, which permitted the capture of high strain rate elastic modulus data. The strain rate dependency of GFPP’s failure strengths in the in-plane and through-thickness direction is modelled using a logarithmic law.

  13. Immune response to Bifidobacterium bifidum strains support Treg/Th17 plasticity.

    Directory of Open Access Journals (Sweden)

    Patricia López

    Full Text Available In this work we analyzed the immune activation properties of different Bifidobacterium strains in order to establish their ability as inductors of specific effector (Th or regulatory (Treg responses. First, we determined the cytokine pattern induced by 21 Bifidobacterium strains in peripheral blood mononuclear cells (PBMCs. Results showed that four Bifidobacterium bifidum strains showed the highest production of IL-17 as well as a poor secretion of IFNγ and TNFα, suggesting a Th17 profile whereas other Bifidobacterium strains exhibited a Th1-suggestive profile. Given the key role of Th17 subsets in mucosal defence, strains suggestive of Th17 responses and the putative Th1 Bifidobacterium breve BM12/11 were selected to stimulate dendritic cells (DC to further determine their capability to induce the differentiation of naïve CD4(+ lymphocytes toward different Th or Treg cells. All selected strains were able to induce phenotypic DC maturation, but showed differences in cytokine stimulation, DC treated with the putative Th17 strains displaying high IL-1β/IL-12 and low IL-12/IL-10 index, whereas BM12/11-DC exhibited the highest IL-12/IL-10 ratio. Differentiation of naïve lymphocytes confirmed Th1 polarization by BM12/11. Unexpectedly, any B. bifidum strain showed significant capability for Th17 generation, and they were able to generate functional Treg, thus suggesting differences between in vivo and vitro responses. In fact, activation of memory lymphocytes present in PBMCS with these bacteria, point out the presence in vivo of specific Th17 cells, supporting the plasticity of Treg/Th17 populations and the key role of commensal bacteria in mucosal tolerance and T cell reprogramming when needed.

  14. Texture Control of Aluminum, Iron, and Magnesium Alloy Sheets to Increase Their Plastic Strain Ratios

    Science.gov (United States)

    Lee, Dong Nyung; Han, Heung Nam

    2011-08-01

    It is known that the limiting drawing ratio of sheet metals is proportional to their plastic strain ratios, and the plastic strain ratios of fcc and bcc metal sheets increase with increasing //ND component in their textures. Conventional cold rolling and subsequent annealing of fcc metals cannot give rise to the //ND component. Specifically, the cold rolling texture of polycrystalline fcc metals is characterized by the fiber connecting the {112}, {123}, and {011} orientations in the Euler space, which is often called the β-fiber. The density of each component in the fiber depends on the stacking fault energy of metals. The {112} and {123} textured Al alloy sheets evolve the {001} texture, when recrystallized. The low plastic strain ratios of the Al alloy sheets are attributed to the {001} texture. The //ND texture can be obtained in shear deformed fcc sheets. Bcc steels develop the //ND texture when cold rolled and recrystallized. However, the density of //ND depends on the content of dissolved interstitial elements such as carbon and nitrogen. The density of the //ND component decreases with increasing concentration of the dissolved interstitial elements. For a given steel, the density of the //ND component can vary with varying thermomechanical treatment. Magnesium alloy sheets are subjected to sheet forming processes at temperatures of 200 °C or higher because of their basal plane texture, or the //ND orientation. Many studies have been made to alleviate the component so that the magnesium alloy sheets can have better formability. In this article, the above issues are briefly reviewed and discussed.

  15. Assessment of myocardial strain and strain rate by tissue doppler echocar-diography

    Directory of Open Access Journals (Sweden)

    Ekimova N.A.

    2013-03-01

    Full Text Available The objective of the article is to review the current data on the method of quantitative evaluation of cardiac mechanics — assessment of myocardial strain and strain rate according to the results of the tissue Doppler echocardiography and prospects of its clinical application.

  16. Numerical simulation of strain localization and damage evolution in large plastic deformation using mixed finite element method

    Institute of Scientific and Technical Information of China (English)

    Zhanghua Chen; Jiajian Jin; Jiumei Xiao

    2004-01-01

    An investigation of computer simulation is presented to analyze the effects of strain localization and damage evolution in large plastic deformation. The simulation is carried out by using an elastic-plastic-damage coupling finite element program that is developed based on the concept of mixed interpolation of displacement/pressure. This program has been incorporated into a damage mechanics model as well as the corresponding damage criterion. To illustrate the performance of the proposed approach, a typical strain localization problem has been simulated. The results show that the proposed approach is of good capability to capture strain localization and predict the damage evolution.

  17. The influence of strain rate and hydrogen on the plane-strain ductility of Zircaloy cladding

    Energy Technology Data Exchange (ETDEWEB)

    Link, T.M.; Motta, A.T.; Koss, D.A. [Pennsylvania State Univ., University Park, PA (United States)

    1998-03-01

    The authors studied the ductility of unirradiated Zircaloy-4 cladding under loading conditions prototypical of those found in reactivity-initiated accidents (RIA), i.e.: near plane-strain deformation in the hoop direction (transverse to the cladding axis) at room temperature and 300 C and high strain rates. To conduct these studies, they developed a specimen configuration in which near plane-strain deformation is achieved in the gage section, and a testing methodology that allows one to determine both the limit strain at the onset of localized necking and the fracture strain. The experiments indicate that there is little effect of strain rate (10{sup {minus}3} to 10{sup 2} s{sup {minus}1}) on the ductility of unhydrided Zircaloy tubing deformed under near plane-strain conditions at either room temperature or 300 C. Preliminary experiments on cladding containing 190 ppm hydrogen show only a small loss of fracture strain but no clear effect on limit strain. The experiments also indicate that there is a significant loss of Zircaloy ductility when surface flaws are present in the form of thickness imperfections.

  18. High Strain Rate Behavior of Polymer Matrix Composites Analyzed

    Science.gov (United States)

    Goldberg, Robert K.; Roberts, Gary D.

    2001-01-01

    Procedures for modeling the high-speed impact of composite materials are needed for designing reliable composite engine cases that are lighter than the metal cases in current use. The types of polymer matrix composites that are likely to be used in such an application have a deformation response that is nonlinear and that varies with strain rate. To characterize and validate material models that could be used in the design of impactresistant engine cases, researchers must obtain material data over a wide variety of strain rates. An experimental program has been carried out through a university grant with the Ohio State University to obtain deformation data for a representative polymer matrix composite for strain rates ranging from quasi-static to high rates of several hundred per second. This information has been used to characterize and validate a constitutive model that was developed at the NASA Glenn Research Center.

  19. Strain rate dependency of laser sintered polyamide 12

    Directory of Open Access Journals (Sweden)

    Cook J.E.T.

    2015-01-01

    Full Text Available Parts processed by Additive Manufacturing can now be found across a wide range of applications, such as those in the aerospace and automotive industry in which the mechanical response must be optimised. Many of these applications are subjected to high rate or impact loading, yet it is believed that there is no prior research on the strain rate dependence in these materials. This research investigates the effect of strain rate and laser energy density on laser sintered polyamide 12. In the study presented here, parts produced using four different laser sintered energy densities were exposed to uniaxial compression tests at strain rates ranging from 10−3 to 10+3 s−1 at room temperature, and the dependence on these parameters is presented.

  20. Effect of strain rate and stress triaxiality on tensile behavior of Titanium alloy Ti-10-2-3 at elevated temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Bobbili, Ravindranadh, E-mail: ravindranadh@dmrl.drdo.in; Madhu, Vemuri

    2016-06-14

    In this study, Split hopkinson tension bar (SHTB) has been employed to investigate the dynamic tensile flow behavior of Ti-10-2-3 alloy at high strain rates and elevated temperatures. The combined effect of stress triaxiality, strain rate and temperature and on the tensile behavior of the alloy was evaluated. Johnson-Cook (J-C) constitutive and fracture models were developed based on high strain rate tensile data. A modified Johnson–Cook model was established and proved to have high accuracy. A comparative assessment has been done to confirm the accuracy of modified J–C model based on finite element method (FEM). The improved model provides better description on the influence of equivalent plastic strain rate and temperature on the plastic flow. The simulation results proved to be in good agreement with the experimental data. The fracture surfaces of specimens tested under various strain rates and temperatures were studied under scanning electron microscopy (SEM).

  1. Analysis of Changing Swarm Rate using Volumetric Strain

    Science.gov (United States)

    Kumazawa, T.; Ogata, Y.; Kimura, K.; Maeda, K.; Kobayashi, A.

    2015-12-01

    Near the eastern coast of Izu peninsula is an active submarine volcanic region in Japan, where magma intrusions have been observed many times. The forecast of earthquake swarm activities and eruptions are serious concern particularly in nearby hot spring resort areas. It is well known that temporal durations of the swarm activities have been correlated with early volumetric strain changes at a certain observation station of about 20 km distance apart. Therefore the Earthquake Research Committee (2010) investigated some empirical statistical relations to predict sizes of the swarm activity. Here we looked at the background seismicity rate changes during these swarm periods using the non-stationary ETAS model (Kumazawa and Ogata, 2013, 2014), and have found the followings. The modified volumetric strain data, by removing the effect of earth tides, precipitation and coseismic jumps, have significantly higher cross-correlations to the estimated background rates of the ETAS model than to the swarm rate-changes. Specifically, the background seismicity rate synchronizes clearer to the strain change by the lags around a half day. These relations suggest an enhanced prediction of earthquakes in this region using volumetric strain measurements. Hence we propose an extended ETAS model where the background rate is modulated by the volumetric strain data. We have also found that the response function to the strain data can be well approximated by an exponential functions with the same decay rate, but that their intersects are inversely proportional to the distances between the volumetric strain-meter and the onset location of the swarm. Our numerical results by the same proposed model show consistent outcomes for the various major swarms in this region.

  2. High-Strain Rate Mechanical Response of Cured Epoxy Networks

    Science.gov (United States)

    Sirk, Timothy; Khare, Ketan; Karim, Mir; Lenhart, Joseph; Khare, Rajesh; Andzelm, Jan

    2013-03-01

    Chemically cross-linked polymer networks are increasingly common in high performance composites, adhesives and other applications involving high-impact loading conditions or ballistic collisions. The mechanical behavior of epoxy and other polymer networks exhibit a strong dependence on strain rate near the glass transition temperature (Tg); however, the elastic modulus at strain rates greater than 105 1/s is difficult to capture with experimental techniques. We present computational results of Di-Glycidyl Ether of Bisphenol A (DGEBA) and Jeffamine diamines (D230) from molecular dynamics simulation, which is intrinsically well-suited to model material deformation at high strain rates. Our results show that the experimental Tg can be reproduced from molecular dynamics, and the Williams-Landel-Ferry equation is useful in rationalizing the shift of Tg due to fast annealing and high strain rates. Temperature sweeps of elastic modulus show the glass-rubber transition to occur over a significantly wider temperature range compared with experimental measurements at low strain rates.

  3. Steady thermal stress and strain rates in a rotating circular cylinder under steady state temperature

    Directory of Open Access Journals (Sweden)

    Pankaj Thakur

    2014-01-01

    Full Text Available Thermal stress and strain rates in a thick walled rotating cylinder under steady state temperature has been derived by using Seth’s transition theory. For elastic-plastic stage, it is seen that with the increase of temperature, the cylinder having smaller radii ratios requires lesser angular velocity to become fully plastic as compared to cylinder having higher radii ratios The circumferential stress becomes larger and larger with the increase in temperature. With increase in thickness ratio stresses must be decrease. For the creep stage, it is seen that circumferential stresses for incompressible materials maximum at the internal surface as compared to compressible material, which increase with the increase in temperature and measure n.

  4. Microstructural Characteristics of High Rate Plastic Deformation in Elektron (trademark) WE43 Magnesium Alloy

    Science.gov (United States)

    2012-04-01

    Microstructural Characteristics of High Rate Plastic Deformation in Elektron ™ WE43 Magnesium Alloy by Joseph Hamilton, Sarah T. Brennan...Ground, MD 21005-5069 ARL-RP-363 April 2012 Microstructural Characteristics of High Rate Plastic Deformation in Elektron ™ WE43 Magnesium...Alloy Joseph Hamilton, Sara T. Brennan, and Yongho Sohn University of Central Florida Bruce Davis and Rick DeLorme Magnesium Elektron North

  5. Elasto-plastic strain analysis by a semi-analytical method

    Indian Academy of Sciences (India)

    Debabrata Das; Prasanta Sahoo; Kashinath Saha

    2008-08-01

    The aim of this paper is to develop a simulation model of large deformation problems following a semi-analytical method, incorporating the complications of geometric and material non-linearity in the formulation. The solution algorithm is based on the method of energy principle in structural mechanics, as applicable for conservative systems. A one-dimensional solid circular bar problem has been solved in post-elastic range assuming linear elastic, linear strain hardening material behaviour. Type of loading includes uniform uniaxial loading and gravity loading due to body force, whereas the geometry of the bar is considered to be non-uniformly taper. Results are validated successfully with benchmark solution and some new results have also been reported. The location of initiation of elasto-plastic front and its growth are found to be functions of geometry of the bar and loading conditions. Some indicative results have been presented for static and dynamic problems and the solution methodology developed for one-dimension has been extended to the elasto-plastic analysis of two-dimensional strain field problems of a rotating disk.

  6. Effects of constitutive parameters on adiabatic shear localization for ductile metal based on JOHNSON-COOK and gradient plasticity models

    Institute of Scientific and Technical Information of China (English)

    WANG Xue-bin

    2006-01-01

    By using the widely used JOHNSON-COOK model and the gradient-dependent plasticity to consider microstmctural effect beyond the occurrence of shear strain localization, the distributions of local plastic shear strain and deformation in adiabatic shear band(ASB) were analyzed. The peak local plastic shear strain is proportional to the average plastic shear strain, while it is inversely proportional to the critical plastic shear strain corresponding to the peak flow shear stress. The relative plastic shear deformation between the top and base of ASB depends on the thickness of ASB and the average plastic shear strain. A parametric study was carried out to study the influence of constitutive parameters on shear strain localization. Higher values of static shear strength and work to heat conversion factor lead to lower critical plastic shear strain so that the shear localization is more apparent at the same average plastic shear strain. Higher values of strain-hardening exponent, strain rate sensitive coefficient, melting point,thermal capacity and mass density result in higher critical plastic shear strain, leading to less apparent shear localization at the same average plastic shear strain. The strain rate sensitive coefficient has a minor influence on the critical plastic shear strain, the distributions of local plastic shear strain and deformation in ASB. The effect of strain-hardening modulus on the critical plastic shear strain is not monotonous. When the maximum critical plastic shear strain is reached, the least apparent shear localization occurs.

  7. A QUASI-FLOW CONSTITUTIVE MODEL WITH STRAIN-RATE DEPENDENCE

    Institute of Scientific and Technical Information of China (English)

    HU Ping; SHEN Guozhe; YANG Guang

    2004-01-01

    In this paper, the proposed is a quasi-flow constitutive model with strain-rate sensitivity for elastic plastic large deformation. The model is based on the Quasi-flow Corner theory,and is suitable for the sheet metal forming process simulation with a variable punch machine velocity.Uniaxial tensile tests and deep-drawing tests of a circular blank with square punch are carried out and numerically simulated. The consistency between the experimental and the numerically simulated results shows the validity of the present new constitutive model.

  8. Effect of Strain Rate on Deformation Behavior of AlCoCrFeNi High-Entropy Alloy by Nanoindentation

    Science.gov (United States)

    Tian, L.; Jiao, Z. M.; Yuan, G. Z.; Ma, S. G.; Wang, Z. H.; Yang, H. J.; Zhang, Y.; Qiao, J. W.

    2016-06-01

    In this study, nanoindentation tests with continuous stiffness measurement technique were measured to investigate the deformation behavior of a high-entropy alloy AlCoCrFeNi under different indentation strain rates at room temperature. Results suggest that the creep behavior exhibits remarkable strain rate dependence. In-situ scanning images showed a conspicuous pileup around the indents, indicating that an extremely localized plastic deformation occurred during the nanoindentation. Under different strain rates, elastic modulus basically remains unchanged, while the hardness decreases with increasing indentation depth due to the indentation size effect. Furthermore, the modulus and hardness of AlCoCrFeNi HEAs are greater than that of the Al x CoCrFeNi ( x = 0.3,0.5) at the strain rate of 0.2 s-1 due to its higher negative enthalpy of mixing related to the atomic binding force, and the solid solution strengthening induced by the lattice distortion, respectively.

  9. Stress, strain rate and anisotropy in Kyushu, Japan

    Science.gov (United States)

    Savage, M. K.; Aoki, Y.; Unglert, K.; Ohkura, T.; Umakoshi, K.; Shimizu, H.; Iguchi, M.; Tameguri, T.; Ohminato, T.; Mori, J.

    2016-04-01

    Seismic anisotropy, the directional dependence of wave speeds, may be caused by stress-oriented cracks or by strain-oriented minerals, yet few studies have quantitatively compared anisotropy to stress and strain over large regions. Here we compare crustal stress and strain rates on the Island of Kyushu, Japan, as measured from inversions of focal mechanisms, GPS and shear wave splitting. Over 85,000 shear wave splitting measurements from local and regional earthquakes are obtained from the NIED network between 2004 and 2012, and on Aso, Sakurajima, Kirishima and Unzen volcano networks. Strain rate measurements are made from the Japanese Geonet stations. JMA-determined S arrival times processed with the MFAST shear wave splitting code measure fast polarisations (Φ), related to the orientation of the anisotropic medium and time delays (dt), related to the path length and the percent anisotropy. We apply the TESSA 2-D delay time tomography and spatial averaging code to the highest quality events, which have nearly vertical incidence angles, separating the 3455 shallow (depth = 40 km) earthquakes. Using square grids with 30 km sides for all the inversions, the best correlations are observed between splitting from shallow earthquakes and stress. Axes of maximum horizontal stress (SHmax) and Φ correlate with a coefficient c of 0.56, significant at the 99% confidence level. Their mean difference is 31.9°. Axes of maximum compressional strain rate and SHmax are also well aligned, with an average difference of 28°, but they do not correlate with each other, meaning that where they differ, the difference is not systematic. Anisotropy strength is negatively correlated with the stress ratio parameter determined from focal mechanism inversion (c = - 0.64; significant at the 99% confidence level). The anisotropy and stress results are consistent with stress-aligned microcracks in the crust in a dominantly strike-slip regime. Eigenvalues of maximum horizontal strain rate

  10. Strain rate dependency and fragmentation pattern of expanding warheads

    Institute of Scientific and Technical Information of China (English)

    John F MOXNES; Anne K PRYTZ; yvind FRYLAND; Stian SKRIUDALEN; Steinar BRVE; Gard DEGRDSTUEN

    2015-01-01

    For the characterization of the behaviors of a metal material in events like expanding warheads, it is necessary to know its strength and ductility at high strain rates, around 104e105/s. The flyer plate impact testing produces the uniform stress and strain rates but the testing is expensive. The Taylor test is relatively inexpensive but produces non-uniform stress and strain fields, and the results are not so easily inferred for material modeling. In the split-Hopkinson bar (SHB), which may be used in compression, tension and torsion testing, the strain rates never exceeds 103/s. In the present work, we use the expanding ring test where the strain rate is 104e105/s. A streak camera is used to examine the expanding ring velocity, and a water tank is used to collect the fragments. The experimental results are compared with the numerical simulations using the hydrocodes AUTODYN, IMPETUS Afea and a regularized smooth particle (RSPH) software. The number of fragments increases with the increase in the expansion velocity of the rings. The number of fragments is similar to the experimental results. The RSPH software shows much the same results as the AUTODYN where the Lagrangian solver is used for the ring. The IMPETUS Afea solver shows a somewhat different fragmentation characteristic due to the node splitting algorithm that induces pronounced tensile splitting.

  11. Strain rate dependency and fragmentation pattern of expanding warheads

    Directory of Open Access Journals (Sweden)

    John F. Moxnes

    2015-03-01

    Full Text Available For the characterization of the behaviors of a metal material in events like expanding warheads, it is necessary to know its strength and ductility at high strain rates, around 104–105/s. The flyer plate impact testing produces the uniform stress and strain rates but the testing is expensive. The Taylor test is relatively inexpensive but produces non-uniform stress and strain fields, and the results are not so easily inferred for material modeling. In the split-Hopkinson bar (SHB, which may be used in compression, tension and torsion testing, the strain rates never exceeds 103/s. In the present work, we use the expanding ring test where the strain rate is 104–105/s. A streak camera is used to examine the expanding ring velocity, and a water tank is used to collect the fragments. The experimental results are compared with the numerical simulations using the hydrocodes AUTODYN, IMPETUS Afea and a regularized smooth particle (RSPH software. The number of fragments increases with the increase in the expansion velocity of the rings. The number of fragments is similar to the experimental results. The RSPH software shows much the same results as the AUTODYN where the Lagrangian solver is used for the ring. The IMPETUS Afea solver shows a somewhat different fragmentation characteristic due to the node splitting algorithm that induces pronounced tensile splitting.

  12. Strain rate orientations near the Coso Geothermal Field

    Science.gov (United States)

    Ogasa, N. T.; Kaven, J. O.; Barbour, A. J.; von Huene, R.

    2016-12-01

    Many geothermal reservoirs derive their sustained capacity for heat exchange in large part due to continuous deformation of preexisting faults and fractures that permit permeability to be maintained. Similarly, enhanced geothermal systems rely on the creation of suitable permeability from fracture and faults networks to be viable. Stress measurements from boreholes or earthquake source mechanisms are commonly used to infer the tectonic conditions that drive deformation, but here we show that geodetic data can also be used. Specifically, we quantify variations in the horizontal strain rate tensor in the area surrounding the Coso Geothermal Field (CGF) by analyzing more than two decades of high accuracy differential GPS data from a network of 14 stations from the University of Nevada Reno Geodetic Laboratory. To handle offsets in the data, from equipment changes and coseismic deformation, we segment the data, perform a piecewise linear fit and take the average of each segment's strain rate to determine secular velocities at each station. With respect to North America, all stations tend to travel northwest at velocities ranging from 1 to 10 mm/yr. The nearest station to CGF shows anomalous motion compared to regional stations, which otherwise show a coherent increase in network velocity from the northeast to the southwest. We determine strain rates via linear approximation using GPS velocities in Cartesian reference frame due to the small area of our network. Principal strain rate components derived from this inversion show maximum extensional strain rates of 30 nanostrain/a occur at N87W with compressional strain rates of 37nanostrain/a at N3E. These results generally align with previous stress measurements from borehole breakouts, which indicate the least compressive horizontal principal stress is east-west oriented, and indicative of the basin and range tectonic setting. Our results suggest that the CGF represents an anomaly in the crustal deformation field, which

  13. Temporal evolution of strain rates at western Greenland moulins

    Science.gov (United States)

    Poinar, Kristin; Andrews, Lauren; Chu, Vena; Moon, Twila; Nowicki, Sophie

    2017-04-01

    Moulins are key sources for subglacial water across western Greenland. The rate and timing at which they deliver surface meltwater to the subglacial system are crucial inputs for ice-sheet hydrology models. Intensive field campaigns coupled to remote sensing efforts have provided, to date, information on the timing of supraglacial lake drainages and water flux through the consequent moulins, but predicting the dates of moulin activation has remained an area of active research. This is vital for the construction of spatially variable basal-input hydrographs for models that will predict the future evolution of Greenland ice flow and sliding. In this study, we combine multiple remote sensing datasets to investigate the degree to which local strain rates can predict moulin activation dates, as indicated by supraglacial lake drainage events. We find that over the period 2009-2011 in the Pâkitsoq region, moulins with more-tensile background (wintertime InSAR-derived) strain rates tend to activate first, followed by moulins in less-tensile background strain regimes. This pattern is relatively consistent across years, although we find that background strain rates are less important in explaining the date of moulin activation than are moulin elevation or cumulative days of runoff. In the Russell Glacier area, we examine the temporal evolution of summertime, Landsat-derived strain rates at moulin locations. Principal component analysis shows that strain rates at moulin locations increased abruptly over June 2012, independent of moulin elevation; strain rates in localities without moulins varied more smoothly in time. We also compare the strain rate time series at each moulin to lake drainage dates derived from MODIS and Landsat imagery from 2012. We hypothesize that the contrasting bedrock topography of the regions (Pâkitsoq is rougher than Russell at the few-km scale) may drive variations in moulin opening patterns across the two regions. Our results will have

  14. Self-citation rate and impact factor in the field of plastic and reconstructive surgery.

    Science.gov (United States)

    Miyamoto, Shimpei

    2017-05-09

    Journal ranking based on the impact factor (IF) can be distorted by self-citation. The aim of this study is to investigate the present status of self-citation in the plastic surgery journals and its effect on the journals' IFs. IF, IF without self-citations (corrected IF), self-cited rate, and self-citing rate for 11 plastic surgery journals were investigated from 2009-2015, by reviewing the Journal Citation Report(®). The correlations of the IF with the self-cited rate and the self-citing rate were statistically assessed. In addition, Plastic and Reconstructive Surgery was compared with 15 top journals from other surgical specialties in 2015. IF was significantly correlated with the self-cited rate (R: 0.594, p = 0.001) and the self-citing rate (R: 0.824, p journals from other surgical specialties. The IFs of Microsurgery and Journal of Cranio-Maxillo-Facial Surgery increased greatly in recent years, but they were inflated by high self-cited and self-citing rates. The self-citation rate positively affects the IF in plastic surgery journals. A high concentration of self-citation of some journals could distort the ranking among plastic surgery journals in general.

  15. Determination of Tensile Properties of Polymers at High Strain Rates

    Directory of Open Access Journals (Sweden)

    Major Z.

    2010-06-01

    Full Text Available In the field of high rate testing of polymers the measured properties are highly dependent on the applied methodology. Hence, the test setup as whole but in particular also the geometrical type of specimen plays a decisive role. The widely used standard for the determination of tensile properties of polymers (ISO527-2 was extended by a novel standard (ISO18872:2007, which is targeted on the determination of tensile properties at high strain rates. In this standard also a novel specimen shape is proposed. Hand in hand with the introduction of new specimen geometry the question of comparability arises. To point out the differences in stress-strain response of the ISO18872 specimen and the ISO527-2 multipurpose specimen tensile tests over a wide loading rate range were conducted in this paper. A digital image correlation system in combination with a high speed camera was used to characterize the local material behaviour. Different parameters like nominal stress, true stress, nominal strain, true strain as well as volumetric strain were determined and used to compare the two specimen geometries.

  16. Slow Strain Rate Testing for Hydrogen Embrittlement Susceptibility of Alloy 718 in Substitute Ocean Water

    Science.gov (United States)

    LaCoursiere, M. P.; Aidun, D. K.; Morrison, D. J.

    2017-05-01

    The hydrogen embrittlement susceptibility of near-peak-aged UNS N07718 (Alloy 718) was evaluated by performing slow strain rate tests at room temperature in air and substitute ocean water. Tests in substitute ocean water were accomplished in an environmental cell that enabled in situ cathodic charging under an applied potential of -1.1 V versus SCE. Some specimens were cathodically precharged for 4 or 16 weeks at the same potential in a 3.5 wt.% NaCl-distilled water solution at 50 °C. Unprecharged specimens tested in substitute ocean water exhibited only moderate embrittlement with plastic strain to failure decreasing by about 20% compared to unprecharged specimens tested in air. However, precharged specimens exhibited significant embrittlement with plastic strain to failure decreasing by about 70%. Test environment (air or substitute ocean water with in situ charging) and precharge time (4 or 16 weeks) had little effect on the results of the precharged specimens. Fracture surfaces of precharged specimens were typical of hydrogen embrittlement and consisted of an outer brittle ring related to the region in which hydrogen infused during precharging, a finely dimpled transition zone probably related to the region where hydrogen was drawn in by dislocation transport, and a central highly dimpled ductile region. Fracture surfaces of unprecharged specimens tested in substitute ocean water consisted of a finely dimpled outer ring and heavily dimpled central region typical of ductile fracture.

  17. Enhancement of Biodegradable Plastic-degrading Enzyme Production from Paraphoma-like Fungus, Strain B47-9.

    Science.gov (United States)

    Sameshima-Yamashita, Yuka; Koitabashi, Motoo; Tsuchiya, Wataru; Suzuki, Ken; Watanabe, Takashi; Shinozaki, Yukiko; Yamamoto-Tamura, Kimiko; Yamazaki, Toshimasa; Kitamoto, Hiroko

    2016-01-01

    To improve the productivity of Paraphoma-like fungal strain B47-9 for biodegradable plastic (BP)-degrading enzyme (PCLE), the optimal concentration of emulsified poly(butylene succinate-co-adipate) (PBSA) in the medium was determined. Emulsified PBSA was consumed as a sole carbon source and an inducer of PCLE production by strain B47-9. Among the various concentrations of emulsified PBSA [0.09-0.9% (w/v)] used in flask cultivation, 0.27% yielded the maximum enzyme activity within a short cultivation period. To evaluate the residual concentration of emulsified PBSA in culture, emulsified PBSA in aliquots of culture supernatant was digested in vitro, and the concentration of released monomerised succinic acid was determined. Regardless of the initial concentration of emulsified PBSA in medium, PCLE activity was detected after residual succinic acid decreased below 0.04 mg/mL in culture broth. Jarfermentation was performed at a 0.27% PBSA concentration. Among the various airflow rates tested, 1 LPM resulted in a PCLE production rate of 1.0 U/mL/day. The enzyme activity in the resulting culture filtrate (4.2 U/2 mL) was shown to degrade commercial BP films (1 × 1 cm, 20 µm thickness) within 8 hours.

  18. Recent advances in echocardiography: strain and strain rate imaging [version 1; referees: 3 approved

    Directory of Open Access Journals (Sweden)

    Oana Mirea

    2016-04-01

    Full Text Available Deformation imaging by echocardiography is a well-established research tool which has been gaining interest from clinical cardiologists since the introduction of speckle tracking. Post-processing of echo images to analyze deformation has become readily available at the fingertips of the user. New parameters such as global longitudinal strain have been shown to provide added diagnostic value, and ongoing efforts of the imaging societies and industry aimed at harmonizing methods will improve the technique further. This review focuses on recent advances in the field of echocardiographic strain and strain rate imaging, and provides an overview on its current and potential future clinical applications.

  19. A fast and accurate method for echocardiography strain rate imaging

    Science.gov (United States)

    Tavakoli, Vahid; Sahba, Nima; Hajebi, Nima; Nambakhsh, Mohammad Saleh

    2009-02-01

    Recently Strain and strain rate imaging have proved their superiority with respect to classical motion estimation methods in myocardial evaluation as a novel technique for quantitative analysis of myocardial function. Here in this paper, we propose a novel strain rate imaging algorithm using a new optical flow technique which is more rapid and accurate than the previous correlation-based methods. The new method presumes a spatiotemporal constancy of intensity and Magnitude of the image. Moreover the method makes use of the spline moment in a multiresolution approach. Moreover cardiac central point is obtained using a combination of center of mass and endocardial tracking. It is proved that the proposed method helps overcome the intensity variations of ultrasound texture while preserving the ability of motion estimation technique for different motions and orientations. Evaluation is performed on simulated, phantom (a contractile rubber balloon) and real sequences and proves that this technique is more accurate and faster than the previous methods.

  20. Discrete dislocation plasticity analysis of loading rate-dependent static friction

    Science.gov (United States)

    Song, H.; Deshpande, V. S.; Van der Giessen, E.

    2016-08-01

    From a microscopic point of view, the frictional force associated with the relative sliding of rough surfaces originates from deformation of the material in contact, by adhesion in the contact interface or both. We know that plastic deformation at the size scale of micrometres is not only dependent on the size of the contact, but also on the rate of deformation. Moreover, depending on its physical origin, adhesion can also be size and rate dependent, albeit different from plasticity. We present a two-dimensional model that incorporates both discrete dislocation plasticity inside a face-centred cubic crystal and adhesion in the interface to understand the rate dependence of friction caused by micrometre-size asperities. The friction strength is the outcome of the competition between adhesion and discrete dislocation plasticity. As a function of contact size, the friction strength contains two plateaus: at small contact length (≲0.6 μ m), the onset of sliding is fully controlled by adhesion while for large contact length (≳10 μ m), the friction strength approaches the size-independent plastic shear yield strength. The transition regime at intermediate contact size is a result of partial de-cohesion and size-dependent dislocation plasticity, and is determined by dislocation properties, interfacial properties as well as by the loading rate.

  1. Simple structures test for elastic-plastic strain acceptance criterion validation

    Energy Technology Data Exchange (ETDEWEB)

    Trimble, T.F. [Electric Boat Corp., Groton, CT (United States); Krech, G.R. [Wyle Labs., Inc., Huntsville, AL (United States)

    1997-11-01

    A Simple Structures Test Program was performed where several cantilevered beam and fixed-end beam test specimens (fabricated from HY-80 steel) were subjected to a series of analytically predetermined rapidly applied transient dynamic input loads. The primary objective of the test program was to obtain dynamic nonlinear response for simple structures subjected to these load inputs. Data derived from these tests was subsequently used to correlate to analysis predictions to assess the capability to analytically predict elastic-plastic nonlinear material behavior in structures using typical time-dependent (transient) design methods and the ABAQUS finite element analysis code. The installation of a significant amount of instrumentation on these specimens and post-test measurements enabled the monitoring and recording of strain levels, displacements, accelerations, and permanent set. An assessment of modeling parameters such as the element type and mesh refinement was made using these test results. In addition, currently available material models and the incremental time step procedure used in the transient analyses were evaluated. Comparison of test data to analysis results shows that displacements, accelerations, and peak strain can be predicted with a reasonable level of accuracy using detailed solid models of the tested specimens. Permanent set is overpredicted by a factor of approximately two. However, the accuracy of the prediction of permanent set is being enhanced by updating material modeling in the ABAQUS code to account for effects of strain reversal in oscillatory behavior of dynamically loaded specimens.

  2. Effect of the strain rate on the mechanical properties of a sheet TRIP steel with a high martensite content

    Science.gov (United States)

    Eliseev, E. A.; Terent'ev, V. F.; Voznesenskaya, N. M.; Slizov, A. K.; Sirotinkin, V. P.; Baikin, A. S.; Seval'nev, G. S.

    2017-04-01

    The laws of changing the mechanical properties of sheet austenitic-martensitic VNS9-Sh (23Kh15N5AM3-Sh) TRIP steel are studied when the static strain rate changes in the range 0.1-20 mm/min (8.3 × 10-5-17 × 10-3 s-1). The 0.35-mm strip under study is characterized by a high martensite content (≈100%) in the surface layer at an average content of 80-85%. The transformation induced plasticity effect is maximal at a strain rate of 0.1 mm/min (8.3 × 10-5 s-1).

  3. Soft Tissue Strain Rates in Side-Blast Incidents

    Science.gov (United States)

    2014-11-02

    for Human Head Impacts. Proceedings ASME Biomechanics of Human Factors Conference. [22] Hannon P, Knapp K. 2006. Forensic Biomechanics. Lawyers...J, Song, B, Pintar, F, Yoganandan N, Chen W, Gennarelli TA. 2008. How to test brain and brain simulant at ballistic and blast strain rates. Rocky

  4. Dynamics of a seismogenic fault subject to variable strain rate

    Directory of Open Access Journals (Sweden)

    M. Dragoni

    2011-06-01

    Full Text Available The behaviour of seismogenic faults is generally investigated under the assumption that they are subject to a constant strain rate. We consider the effect of a slowly variable strain rate on the recurrence times of earthquakes generated by a single fault. To this aim a spring-block system is employed as a low-order analog of the fault. Two cases are considered: a sinusoidal oscillation in the driver velocity and a monotonic change from one velocity value to another. In the first case, a study of the orbit of the system in the state space suggests that the seismic activity of the equivalent fault is organized into cycles that include several earthquakes and repeat periodically. Within each cycle the recurrence times oscillate about an average value equal to the recurrence period for constant strain rate. In the second case, the recurrence time changes gradually from the value before the transition to the value following it. Asymptotic solutions are also given, approximating the case when the amplitude of the oscillation or of the monotonic change is much smaller than the average driver velocity and the period of oscillation or the duration of the transition is much longer than the recurrence times of block motions. If the system is not isolated but is subject to perturbations in stress, the perturbation anticipates or delays the subsequent earthquake. The effects of stress perturbations in the two cases of strain rate oscillations and monotonic change are considered.

  5. High Strain-Rate Testing of Mechanical Couplers

    Science.gov (United States)

    2009-09-01

    tensile strength equal to or greater than that of the control bar but did not achieve the ductility of the control bar. Specimen UHC 9 failed close to...than the Grade 60 bar, but only slightly so at the rapid rate. Upset head system The upset head coupler ( UHC ) system performed very well under the...average performance of the UHC system under the intermediate strain-rate loading condition produced 99% of the dynamic ultimate strength, 61% of the

  6. Analysis of FCC sheet metal forming with rate-independent polycrystalline plasticity FEM

    Institute of Scientific and Technical Information of China (English)

    张少睿; 李大永; 罗应兵; 彭颖红

    2004-01-01

    A rate-independent polycrystalline plasticity constitutive model considering self and latent hardening was developed. Next, a new orientation probability assignment method was proposed and the crystal orientations were assigned to Ft integration points, which represent crystals and can rotate individually. Then cup drawing of FCC aluminum sheet was studied using crystalline plasticity finite element analysis. The results show that the validity of nealing aluminum sheet, due to the balance between two main textures, the flange earing tendency is not obvious.

  7. The role of dissipation and defect energy in variational formulations of problems in strain-gradient plasticity. Part 2: single-crystal plasticity

    Science.gov (United States)

    Reddy, B. D.

    2011-11-01

    Variational formulations are constructed for rate-independent problems in small-deformation single-crystal strain-gradient plasticity. The framework, based on that of Gurtin (J Mech Phys Solids 50: 5-32, 2002), makes use of the flow rule expressed in terms of the dissipation function. Provision is made for energetic and dissipative microstresses. Both recoverable and non-recoverable defect energies are incorporated into the variational framework. The recoverable energies include those that depend smoothly on the slip gradients, the Burgers tensor, or on the dislocation densities (Gurtin et al. J Mech Phys Solids 55:1853-1878, 2007), as well as an energy proposed by Ohno and Okumura (J Mech Phys Solids 55:1879-1898, 2007), which leads to excellent agreement with experimental results, and which is positively homogeneous and therefore not differentiable at zero slip gradient. Furthermore, the variational formulation accommodates a non-recoverable energy due to Ohno et al. (Int J Mod Phys B 22:5937-5942, 2008), which is also positively homogeneous, and a function of the accumulated dislocation density. Conditions for the existence and uniqueness of solutions are established for the various examples of defect energy, with or without the presence of hardening or slip resistance.

  8. High Strain Rate Testing of Welded DOP-26 Iridium

    Energy Technology Data Exchange (ETDEWEB)

    Schneibel, J. H. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Miller, R. G. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Carmichael, C. A. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Fox, E. E. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Ulrich, G. B. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); George, E. P. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2017-08-01

    The iridium alloy DOP-26 is used to produce Clad Vent Set cups that protect the radioactive fuel in radioisotope thermoelectric generators (RTGs) which provide electric power for spacecraft and rovers. In a previous study, the tensile properties of DOP-26 were measured over a wide range of strain rates and temperatures and reported in ORNL/TM-2007/81. While that study established the properties of the base material, the fabrication of the heat sources requires welding, and the mechanical properties of welded DOP-26 have not been extensively characterized in the past. Therefore, this study was undertaken to determine the mechanical properties of DOP-26 specimens containing a transverse weld in the center of their gage sections. Tensile tests were performed at room temperature, 750, 900, and 1090°C and engineering strain rates of 1×10-3 and 10 s-1. Room temperature testing was performed in air, while testing at elevated temperatures was performed in a vacuum better than 1×10-4 Torr. The welded specimens had a significantly higher yield stress, by up to a factor of ~2, than the non-welded base material. The yield stress did not depend on the strain rate except at 1090°C, where it was slightly higher for the faster strain rate. The ultimate tensile stress, on the other hand, was significantly higher for the faster strain rate at temperatures of 750°C and above. At 750°C and above, the specimens deformed at 1×10-3 s-1 showed pronounced necking resulting sometimes in perfect chisel-edge fracture. The specimens deformed at 10 s-1 exhibited this fracture behavior only at the highest test temperature, 1090°C. Fracture occurred usually in the fusion zone of the weld and was, in most cases, primarily intergranular.

  9. Strain-dependent variations in spatial learning and in hippocampal synaptic plasticity in the dentate gyrus of freely behaving rats

    Directory of Open Access Journals (Sweden)

    Denise eManahan-Vaughan

    2011-03-01

    Full Text Available Hippocampal synaptic plasticity is believed to comprise the cellular basis for spatial learning. Strain-dependent differences in synaptic plasticity in the CA1 region have been reported. However, it is not known whether these differences extend to other synapses within the trisynaptic circuit, although there is evidence for morphological variations within that path. We investigated whether Wistar and Hooded Lister (HL rat strains express differences in synaptic plasticity in the dentate gyrus in vivo. We also explored whether they exhibit differences in the ability to engage in spatial learning in an 8-arm radial maze. Basal synaptic transmission was stable over a 24h period in both rat strains, and the input-output relationship of both strains was not significantly different. Paired-pulse analysis revealed significantly less paired-pulse facilitation in the Hooded Lister strain when pulses were given 40-100 msec apart. Low frequency stimulation at 1Hz evoked long-term depression (>24h in Wistar and short-term depression (<2h in HL rats; 200Hz stimulation induced long-term potentiation (>24h in Wistar, and a transient, significantly smaller potentiation (<1h in HL rats, suggesting that HL rats have higher thresholds for expression of persistent synaptic plasticity. Training for 10d in an 8-arm radial maze revealed that HL rats master the working memory task faster than Wistar rats, although both strains show an equivalent performance by the end of the trial period. HL rats also perform more efficiently in a double working and reference memory task. On the other hand, Wistar rats show better reference memory performance on the final (8-10 days of training. Wistar rats were less active and more anxious than HL rats.These data suggest that strain-dependent variations in hippocampal synaptic plasticity occur in different hippocampal synapses. A clear correlation with differences in spatial learning is not evident however.

  10. Equal perimeter yield criterion and its specific plastic work rate: Development, validation and application

    Institute of Scientific and Technical Information of China (English)

    章顺虎; 赵德文; 陈晓东

    2015-01-01

    In order to overcome the nonlinearity of Mises criterion, a new linear yield criterion with a dodecagon shape of the same perimeter as Mises criterion was derived by means of geometrical analysis. Its specific plastic work rate expressed as a linear function of the yield stress, the maximum and minimum strains was also deduced and compared with that of Mises criterion. The physical meaning of the proposed yield criterion is that yielding of materials begins when the shear yield stress τs reaches the magnitude of 0.594σs. By introducing the Lode parameter, validation of evolution expressions of the proposed yield criterion with those based on Tresca, Mises and TSS criteria as well as available classical yield experimental results of various metals shows that the present results intersect with Mises results and coincide well with experimental data. Moreover, further application to the limit analysis of circle plate as an example is performed to demonstrate the effectiveness of the proposed yield criterion, and the subsequent comparison of limit loads with the Tresca analytical solutions and Mises numerical results shows that the present results are higher than the Tresca analytical results, and are in good agreement with the Mises numerical results.

  11. An Evaluation of Constitutive Laws and their Ability to Predict Flow Stress over Large Variations in Temperature, Strain, and Strain Rate Characteristic of Friction Stir Welding

    Science.gov (United States)

    Kuykendall, Katherine

    2011-07-01

    Constitutive laws commonly used to model friction stir welding have been evaluated, both qualitatively and quantitatively, and a new application of a constitutive law which can be extended to materials commonly used in FSW is presented. Existing constitutive laws have been classified as path-dependent or path-independent. Path-independent laws have been further classified according to the physical phenomena they capture: strain hardening, strain rate hardening, and/or thermal softening. Path-dependent laws can track gradients in temperature and strain rate characteristic to friction stir welding; however, path-independent laws cannot. None of the path-independent constitutive laws evaluated has been validated over the full range of strain, strain rate, and temperature in friction stir welding. Holding all parameters other than constitutive law constant in a friction stir weld model resulted in temperature differences of up to 21%. Varying locations for maximum temperature difference indicate that the constitutive laws resulted in different temperature profiles. The Sheppard and Wright law is capable of capturing saturation but incapable of capturing strain hardening with errors as large as 57% near yield. The Johnson-Cook law is capable of capturing strain hardening; however, its inability to capture saturation causes over-predictions of stress at large strains with errors as large as 37% near saturation. The Kocks and Mecking model is capable of capturing strain hardening and saturation with errors less than 5% over the entire range of plastic strain. The Sheppard and Wright and Johnson-Cook laws are incapable of capturing transients characteristic of material behavior under interrupted temperature or strain rate. The use of a state variable in the Kocks and Mecking law allows it to predict such transients. Constants for the Kocks and Mecking model for AA 5083, AA 3004, and Inconel 600 were determined from Atlas of Formability data. Constants for AA 5083 and AA

  12. Recrystallization of High Carbon Steel during High Strain Rate

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The recrystallization of high carbon steel during high temperature and high speed rolling has been studied by analyzing the stress-strain curves and the austenite grain size.Isothermal multi-pass hot compression at high strain rate was carried out by Gleeble-2000. The austenite grain size was measured by IBAS image analysis system. The results show that static recrystallization occurred at interpass time under pre-finish rolling, and at the finish rolling stage, due to the brief interpass time, static recrystallization can not be found.

  13. Measurement of the stress/strain response of energetic materials as a function of strain rate and temperature: PBX 9501 and Mock 9501

    Energy Technology Data Exchange (ETDEWEB)

    Funk, D.J.; Laabs, G.W.; Peterson, P.D.; Asay, B.W.

    1995-09-01

    We have measured the stress/strain behavior of PBX 9501, Mock 900-21 and two new mocks consisting of monoclinic granular sugar embedded in (1) a BDNPA-F/estane binder (a 9501 material mock; a hard organic crystal embedded in a plastic) and (2) neat estane (an LX-14 mock) at strain rates from 10{sup -3} to 10{sup -1}, at two L/D`s and at two temperatures (25 and 60 C). We find that the compressive strength falls with increasing temperature and rises with increasing strain rate. We also find that the new 9501 sugar mock most closely resembles the behavior of the 9501 explosive and differences may be attributable to the different ages of the estane binder used.

  14. Stress-strain characteristics of materials at high strain rates. Part II. Experimental results

    Energy Technology Data Exchange (ETDEWEB)

    Ripperger, E. A. [Texas. Univ., Austin, TX (US). Structural Mechanics Research Lab.

    1958-08-29

    These two reports were issued separately, but are cataloged as a unit. A photoelectric method for measuring displacements during high-velocity impacts is described. The theory of the system is discussed in detail, and a prototype system which was built and tested is described. The performance of the prototype system is evaluated by comparing the results which it gives with results obtained by other methods of measurement. The system was found capable of a resolution of at least 0.01 inches. static and dynamic stress-strain characteristics of seven high polymers, polyethylene, teflon, nylon, tenite M, tenite H, polystyrene, and saran, plus three metals, lead, copper, and aluminum, are described and compared by means of stress-strain curves and photographs. Data are also presented which show qualitatively the effects produced on stress-strain characteristics by specimen configuration, temperature, and impact velocity. It is shown that there is a definite strain-rate effect for all these materials except polystyrene. The effect is one of an apparent stiffening of the material with increasing strain rate, which is similar to the effect produced by lowering the temperature. The stress-strain measurements are examined critically, inconsistencies are pointed out, and possible sources of error suggested. Values of yield stress, modulus of elasticity and energy absorption for all materials (except copper and aluminum), specimen configurations, temperatures, and impact velocities included in the investigation are tabulated.

  15. Model for charge/discharge-rate-dependent plastic flow in amorphous battery materials

    Science.gov (United States)

    Khosrownejad, S. M.; Curtin, W. A.

    2016-09-01

    Plastic flow is an important mechanism for relaxing stresses that develop due to swelling/shrinkage during charging/discharging of battery materials. Amorphous high-storage-capacity Li-Si has lower flow stresses than crystalline materials but there is evidence that the plastic flow stress depends on the conditions of charging and discharging, indicating important non-equilibrium aspects to the flow behavior. Here, a mechanistically-based constitutive model for rate-dependent plastic flow in amorphous materials, such as LixSi alloys, during charging and discharging is developed based on two physical concepts: (i) excess energy is stored in the material during electrochemical charging and discharging due to the inability of the amorphous material to fully relax during the charging/discharging process and (ii) this excess energy reduces the barriers for plastic flow processes and thus reduces the applied stresses necessary to cause plastic flow. The plastic flow stress is thus a competition between the time scales of charging/discharging and the time scales of glassy relaxation. The two concepts, as well as other aspects of the model, are validated using molecular simulations on a model Li-Si system. The model is applied to examine the plastic flow behavior of typical specimen geometries due to combined charging/discharging and stress history, and the results generally rationalize experimental observations.

  16. EFFECTS OF TEST TEMPERATURE AND STRAIN RATE ON THE MECHANICAL PROPERTIES IN AN INTERCRITICALLY HEAT-TREATED BAINITE-TRANSFORMED STEEL

    Institute of Scientific and Technical Information of China (English)

    Z. Li; D. Wu

    2004-01-01

    Larger amount of austenite could be retained in an intercritically heat-treated bainitetransformed steel. The elongation and the strength-ductility balance of the steel could be enhanced considerably due to strain-induced martensite transformation and transformationinduced plasticity (TRIP) of retained austenite. The effects of test temperature and strain rate on the mechanical properties and strain induced transformation behavior of retained austenite in the steel were investigated. Total elongation and strength-ductility balance of the specimen reached maximum when it strained at a strain rate of 2.8×10-4s-1 and at 350℃. The relation between test temperature and tensile properties showed the same tendency at three kinds of strain rates. Flow stress increased considerably with decreasing the strain rate.

  17. Composite Behavior of Lath Martensite Steels Induced by Plastic Strain, a New Paradigm for the Elastic-Plastic Response of Martensitic Steels

    Science.gov (United States)

    Ungár, Tamás; Harjo, Stefanus; Kawasaki, Takuro; Tomota, Yo; Ribárik, Gábor; Shi, Zengmin

    2017-01-01

    Based on high-resolution neutron diffraction experiments, we will show that in lath martensite steels, the initially homogeneous dislocation structure, i.e., homogeneous on the length scale of grain size, is disrupted by plastic deformation, which, in turn, produces a composite on the length scale of martensite lath packets. The diffraction patterns of plastically strained martensitic steel reveal characteristically asymmetric peak profiles in the same way as has been observed in materials with heterogeneous dislocation structures. The quasi homogeneous lath structure, formed by quenching, is disrupted by plastic deformation producing a composite structure. Lath packets oriented favorably or unfavorably for dislocation glide become soft or hard. Two lath packet types develop by work softening or work hardening in which the dislocation densities become smaller or larger compared to the initial average dislocation density. The decomposition into soft and hard lath packets is accompanied by load redistribution and the formation of long-range internal stresses between the two lath packet types. The composite behavior of plastically deformed lath martensite opens a new way to understand the elastic-plastic response in this class of materials.

  18. A Comparison of Geodetic Strain Rates With Earthquake Moment Tensors

    Science.gov (United States)

    Zhu, W.; Holt, W. E.

    2004-12-01

    In this paper we compare the global model from interpolation of GPS data with the global model inferred from earthquake moment tensors. We use the Harvard CMT catalog to calculate moment rates based on 3 assumptions: a. we assume earthquakes are self-similar; b. we assume a uniform Beta value of the Gutenberg-Richter distribution; c. we assume that all of the long-term strain is accommodated seismically. If these assumptions are correct then the seismicity rate is proportional to the tectonic moment rate. We then inferred a long-term moment rate tensor field estimate for all plate boundary zones from which we inferred a long-term seismic strain rate estimate. Using this estimate we solved for a self-consistent kinematic global solution (motions of rigid spherical caps and motions within plate boundary zones) using bi-cubic spline interpolation of the inferred strain rates. We tested the above assumptions by comparing the global kinematic model obtained from earthquake data with a global model inferred from interpolation of space geodetic data [Kreemer et al., 2003]. A comparison between the two models shows good agreement for motion directions of the North American, and Eurasian plates and for the plate boundary zones within these regions (e.g., Tibet). Problems arise, and our assumptions break down, for plates adjacent to fast spreading ridges where divergence of plates appears to be accommodated aseismically. We next investigated the correlation of strain rate tensor inferred from the interpolation of GPS observations within deforming Asia with the earthquake moment tensors, using both elastic and viscous rheologies. Our solutions satisfy the force balance equations for a given rheology. Our goal for this exercise is to investigate whether the interseismic signal, inferred from GPS, correlates better with moment tensor style for an elastic rheology as opposed to a viscous rheology. Results to date suggest that the viscous models only provide a better agreement

  19. Material properties of bovine intervertebral discs across strain rates.

    Science.gov (United States)

    Newell, Nicolas; Grigoriadis, Grigorios; Christou, Alexandros; Carpanen, Diagarajen; Masouros, Spyros D

    2017-01-01

    The intervertebral disc (IVD) is a complex structure responsible for distributing compressive loading to adjacent vertebrae and allowing the vertebral column to bend and twist. To study the mechanical behaviour of individual components of the IVD, it is common for specimens to be dissected away from their surrounding tissues for mechanical testing. However, disrupting the continuity of the IVD to obtain material properties of each component separately may result in erroneous values. In this study, an inverse finite element (FE) modelling optimisation algorithm has been used to obtain material properties of the IVD across strain rates, therefore bypassing the need to harvest individual samples of each component. Uniaxial compression was applied to ten fresh-frozen bovine intervertebral discs at strain rates of 10(-3)-1/s. The experimental data were fed into the inverse FE optimisation algorithm and each experiment was simulated using the subject specific FE model of the respective specimen. A sensitivity analysis revealed that the IVD's response was most dependent upon the Young's modulus (YM) of the fibre bundles and therefore this was chosen to be the parameter to optimise. Based on the obtained YM values for each test corresponding to a different strain rate (ε̇), the following relationship was derived:YM=35.5lnε̇+527.5. These properties can be used in finite element models of the IVD that aim to simulate spinal biomechanics across loading rates. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

  20. Deduction of plastic work rate per unit volume for unified yield criterion and its application

    Institute of Scientific and Technical Information of China (English)

    ZHAO De-wen; LI Jing; LIU Xiang-hua; WANG Guo-dong

    2009-01-01

    A unified linear expression of plastic work rate per unit volume is deduced from the unified linear yield criterion and the associated flow rule. The expression is suitable for various linear yield loci in the error triangle between Tresca's and twin shear stress yield loci on the π-plane. It exhibits generalization in which the different value of criterion parameter b corresponds to a specific linear formula of plastic work rate per unit volume. Finally, with the unified linear expression of plastic work rate and upper-bound parallel velocity field the strip forging without bulge is successfully analyzed and an analytical result is also obtained. The comparison with traditional solutions shows that when b=1/(1+(√3)) the result is the same as the upper bound result by Mises' yield criterion, and it also is identical to that by slab method with m=1, σ0=0.

  1. Reaction weakening and emplacement of crystalline thrusts: Diffusion control on reaction rate and strain rate

    Science.gov (United States)

    O'Hara, Kieran

    2007-08-01

    In the southern Appalachians, the Blue Ridge-Piedmont crystalline thrust sheet was emplaced onto low-grade Late Precambrian and Paleozoic sedimentary rocks in the footwall along a basal detachment consisting of phyllosilicate-rich mylonites (phyllonites). The phyllonites developed first by mechanical breakdown of feldspar followed by chemical breakdown to white mica in the presence of a pore fluid. Diffusion of solute in the pore fluid is the rate limiting step in controlling reaction rate and also the strain rate. Assuming solute diffusion follows the Stokes-Einstein equation, the shear strain rate is given by ⅆγ/ⅆt=2ωkT/5ηrx for shear stress ≥20 MPa, where n is a constant, ω is a geometric factor, k is Boltzmann's constant, T is absolute temperature, η is water viscosity, r is the atomic radius of the diffusing species, and x is the diffusion distance. A bulk diffusion coefficient in the range of ˜10 -10 to 10 -12 m 2/s over distances of 10-100 m results in strain rates of 10 -14 to 10 -13 s -1 in the temperature range 200-400 °C. It is concluded that greenschist grade crystalline thrust sheets develop on pre-existing basement faults that become weak during reaction softening and localize into high strain phyllonite zones in which pore fluid diffusion controls reaction rate and strain rate.

  2. Finite Strain Behavior of Polyurea for a Wide Range of Strain Rates

    Science.gov (United States)

    2010-02-01

    influence of a surface coating on the high-rate fragmentation of a ductile material ," International Journal of Fracture , 137:89-108. [40] Haupt, P. and Lion...of localization and fragmentation - III. Effect of cladding with a polymer," International Journal of Fracture , 155:101-118. [107] Zhao, H. and Gary... toughness -to-density ratio and high strain rate-sensitivity, so its application is recently extended to structural purpose to form sandwich-type or multi

  3. Influence of plastic strain on the hydrogen evolution reaction on nickel (100) single crystal surfaces to improve hydrogen embrittlement

    Energy Technology Data Exchange (ETDEWEB)

    Lekbir, C., E-mail: choukri.lekbir@univ-lr.fr; Creus, J.; Sabot, R.; Feaugas, X.

    2013-08-20

    Hydrogen-induced embrittlement can be accountable for premature failure of structure in relation with physical and/or chemical processes occurring on material's surface or in the bulk of the material. Hydrogen Evolution Reaction (HER) corresponding to the early step of hydrogen ingress in the material is explored in present study in relation with plastic strain. HER on nickel (100) single crystal in sulphuric acid medium can be related by a Volmer–Heyrovsky mechanism. The corresponding elementary kinetic parameters as symmetry coefficients, activation enthalpies, and number of active sites have been identified via a thermokinetic model using experimental data. These parameters can be affected by defects associated with plastic strain. Irreversible plastic strain modifies the density and the distribution of storage dislocations affecting the surface roughness at atomic scale and generating additional active adsorption sites. Furthermore, surface emergence of mobile dislocations induces the formation of slip bands, which modify the surface roughness and the electronic state of the surface and increases the (111) surface density. The consequence of plastic strain on HER is explored and discussed in relation with both processes.

  4. Cutinase-like enzyme from the yeast Cryptococcus sp. strain S-2 hydrolyzes polylactic acid and other biodegradable plastics.

    Science.gov (United States)

    Masaki, Kazuo; Kamini, Numbi Ramudu; Ikeda, Hiroko; Iefuji, Haruyuki

    2005-11-01

    A purified lipase from the yeast Cryptococcus sp. strain S-2 exhibited remote homology to proteins belonging to the cutinase family rather than to lipases. This enzyme could effectively degrade the high-molecular-weight compound polylactic acid, as well as other biodegradable plastics, including polybutylene succinate, poly (epsilon-caprolactone), and poly(3-hydroxybutyrate).

  5. ELASTO-PLASTIC CONSTITUTIVE MODEL OF SOIL-STRUCTURE INTERFACE IN CONSIDERATION OF STRAIN SOFTENING AND DILATION

    Institute of Scientific and Technical Information of China (English)

    Aizhao Zhou; Tinghao Lu

    2009-01-01

    The behavior of soil-structure interface plays a major role in the definition of soil-structure interaction. In this paper a bi-potential surface elasto-plastic model for soil-structure interface is proposed in order to describe the interface deformation behavior, including strain softening and normal dilatancy. The model is formulated in the framework of generalized potential theory, in which the soil-structure interface problem is regard as a two-dimensional mathematical problem in stress field, and plastic state equations are used to replace the traditional field surface. The relation curves of shear stress and tangential strain are fitted by a piecewise function composed by hyperbolic functions and hyperbolic secant functions, while the relation curves of normal strain and tangential strain are fitted by another piecewise function composed by quadratic functions and hyperbolic secant functions. The approach proposed has the advantage of deriving an elasto-plastic constitutive matrix without postulating the plastic potential functions and yield surface. Moreover, the mathematical principle is clear, and the entire model parameters can be identified by experimental tests. Finally, the predictions of the model have been compared with experimental results obtained from simple shear tests under normal stresses, and results show the model is reasonable and practical.

  6. Cutinase-Like Enzyme from the Yeast Cryptococcus sp. Strain S-2 Hydrolyzes Polylactic Acid and Other Biodegradable Plastics

    Science.gov (United States)

    Masaki, Kazuo; Kamini, Numbi Ramudu; Ikeda, Hiroko; Iefuji, Haruyuki

    2005-01-01

    A purified lipase from the yeast Cryptococcus sp. strain S-2 exhibited remote homology to proteins belonging to the cutinase family rather than to lipases. This enzyme could effectively degrade the high-molecular-weight compound polylactic acid, as well as other biodegradable plastics, including polybutylene succinate, poly (ɛ-caprolactone), and poly(3-hydroxybutyrate). PMID:16269800

  7. High strain rate behavior of pure metals at elevated temperature

    Science.gov (United States)

    Testa, Gabriel; Bonora, Nicola; Ruggiero, Andrew; Iannitti, Gianluca; Domenico, Gentile

    2013-06-01

    In many applications and technology processes, such as stamping, forging, hot working etc., metals and alloys are subjected to elevated temperature and high strain rate deformation process. Characterization tests, such as quasistatic and dynamic tension or compression test, and validation tests, such as Taylor impact and DTE - dynamic tensile extrusion -, provide the experimental base of data for constitutive model validation and material parameters identification. Testing material at high strain rate and temperature requires dedicated equipment. In this work, both tensile Hopkinson bar and light gas gun where modified in order to allow material testing under sample controlled temperature conditions. Dynamic tension tests and Taylor impact tests, at different temperatures, on high purity copper (99.98%), tungsten (99.95%) and 316L stainless steel were performed. The accuracy of several constitutive models (Johnson and Cook, Zerilli-Armstrong, etc.) in predicting the observed material response was verified by means of extensive finite element analysis (FEA).

  8. Modeling Strain Rate Effect for Heterogeneous Brittle Materials

    Institute of Scientific and Technical Information of China (English)

    MA Guowei; DONG Aiai; LI Jianchun

    2006-01-01

    Rocks are heterogeneous from the point of microstructure which is of significance to their dynamic failure behavior.Both the compressive and tensile strength of rock-like materials is regarded different from the static strength.The present study adopts smoothed particle hydrodynamics (SPH) which is a virtual particle based meshfree method to investigate strain rate effect for heterogeneous brittle materials.The SPH method is capable of simulating rock fracture,free of the mesh constraint of the traditional FEM and FDM models.A pressure dependent J-H constitutive model involving heterogeneity is employed in the numerical modeling.The results show the compressive strength increases with the increase of strain rate as well as the tensile strength,which is important to the engineering design.

  9. Strain and strain rate: An emerging technology in the perioperative period.

    Science.gov (United States)

    Malik, Vishwas; Subramaniam, Arun; Kapoor, Poonam Malhotra

    2016-01-01

    Newer noninvasive parameters are being used for perioperative detection of myocardial ischaemia. TDI and global strain rate are some of these parameters. TDI signal is a modification of the routine Doppler flow signal. It is obtained by using thresholding and filtering algorithms that reject echoes originating from the blood pool (by-passing the high pass filter). Set-Up of the machine by activating the TDI function allows decreasing the system gain using a low pass filter and eliminates the signal produced by blood flow. Doppler shift obtained from myocardial tissue motion are of higher amplitudes (reflectivity 40 dB higher) and move about 10 times slower than blood (velocity range: 0.06 to 0.24 m/s). Speckle tracking echocardiography (tissue tracking, 2D strain) utilizes routine gray-scale 2D echo images to calculate myocardial strain. Interactions of ultrasound with myocardium result in reflection and scattering. These interactions generate a finely gray-shaded, speckled pattern (acoustic marker). This speckled pattern is unique for each myocardial region and relatively stable throughout the cardiac cycle. Spatial and temporal image processing of acoustic speckles in both 2D and 3D allows for the calculation of myocardial velocity, strain, and Strain rate.

  10. 49 CFR Appendix B to Part 173 - Procedure for Testing Chemical Compatibility and Rate of Permeation in Plastic Packaging and...

    Science.gov (United States)

    2010-10-01

    ... Rate of Permeation in Plastic Packaging and Receptacles B Appendix B to Part 173 Transportation Other... Plastic Packaging and Receptacles 1. The purpose of this procedure is to determine the chemical compatibility and permeability of liquid hazardous materials packaged in plastic packaging and...

  11. Derivation of Plastic Work Rate Done per Unit Volume for Mean Yield Criterion and Its Application

    Institute of Scientific and Technical Information of China (English)

    Dewen ZHAO; Yingjie XIE; Xiaowen WANG; Xianghua LIU

    2005-01-01

    In Haigh Westergaard stress space linear combination of twin shear stress and Tresca yield functions is called the mean yield (MY) criterion. The mathematical relationship of the criterion and its plastic work rate done per unit volume were derived. A generalized worked example of slab forging was analyzed by the criterion and its corresponding plastic work rate done per unit volume. Then, the precision of the solution was compared with those by Mises and Twin shear stress yield criterions, respectively. It turned out that the calculated results by MY criterion were in good agreement with those by Mises criterion.

  12. Strain and strain rate by two-dimensional speckle tracking echocardiography in a maned wolf

    Directory of Open Access Journals (Sweden)

    Matheus M. Mantovani

    2012-12-01

    Full Text Available The measurement of cardiovascular features of wild animals is important, as is the measurement in pets, for the assessment of myocardial function and the early detection of cardiac abnormalities, which could progress to heart failure. Speckle tracking echocardiography (2D STE is a new tool that has been used in veterinary medicine, which demonstrates several advantages, such as angle independence and the possibility to provide the early diagnosis of myocardial alterations. The aim of this study was to evaluate the left myocardial function in a maned wolf by 2D STE. Thus, the longitudinal, circumferential and radial strain and strain rate were obtained, as well as, the radial and longitudinal velocity and displacement values, from the right parasternal long axis four-chamber view, the left parasternal apical four chamber view and the parasternal short axis at the level of the papillary muscles. The results of the longitudinal variables were -13.52±7.88, -1.60±1.05, 4.34±2.52 and 3.86±3.04 for strain (%, strain rate (1/s, displacement (mm and velocity (cm/s, respectively. In addition, the radial and circumferential Strain and Strain rate were 24.39±14.23, 1.86±0.95 and -13.69±6.53, -1.01±0.48, respectively. Thus, the present study provides the first data regarding the use of this tool in maned wolves, allowing a more complete quantification of myocardial function in this species.

  13. Rotation and strain rate of Sulawesi from geometrical velocity field

    Science.gov (United States)

    Sarsito, D. A.; Susilo, Simons, W. J. F.; Abidin, H. Z.; Sapiie, B.; Triyoso, W.; Andreas, H.

    2017-07-01

    One of methods that can be used to determine the tectonic deformation status is rate estimation from geometric rotation and strain using quantitative velocity data from GPS observations. Microplate Sulawesi region located in the zone of triple junction (Eurasia, Australia and Philippine Sea Plates) has very complex tectonic and seismic condition, which is why become very important to know its recent deformation status in order to study neo-tectonic and disaster mitigation. Deformation rate quantification is estimated in two parameters: rotation and geodetic strain rate of each GPS station Delaunay triangle in the study area. The analysis in this study is not done using the grids since there is no rheological information at location that can be used as the interpolation-extrapolation constraints. Our analysis reveals that Sulawesi is characterized by rapid rotation in several different domains and compression-strain pattern that varies depending on the type and boundary conditions of microplate. This information is useful for studying neo tectonic deformation status and earthquake disaster mitigation.

  14. Atomistic simulations of high strain rate loading of nanocrystals

    Science.gov (United States)

    Bringa, E. M.; Tramontina, D.; Ruestes, C. J.; Tang, Y.; Meyers, M. A.; Gunkelmann, N.; Urbassek, H. M.

    2013-03-01

    Materials loaded at high strain rates can reach extreme temperature and pressure conditions. Most experiments on loading of simple materials use poly crystals, while most atomistic simulations of shock wave loading deal with single crystals, due to the higher computational cost of running polycrystal samples. Of course, atomistic simulations of polycrystals with micron-sized grains are beyond the capabilities of current supercomputers. On the other hand, nanocrystals (nc) with grain sizes below 50 nm can be obtained experimentally and modeled reasonably well at high strain rates, opening the possibility of nearly direct comparison between atomistic molecular dynamics (MD) simulations and experiments using high power lasers. We will discuss MD simulations and links to experiments for nc Cu and Ni, as model f.c.c. solids, and nc Ta and Fe, as model b.c.c. solids. In all cases, the microstructure resulting from loading depends strongly on grain size, strain rate and peak applied pressure. We will also discuss effects related to target porosity in nc's. E.M.B. thanks funding from PICT2008-1325.

  15. Microstructure and annealing behavior of a modified 9Cr-1Mo steel after dynamic plastic deformation to different strains

    DEFF Research Database (Denmark)

    Zhang, Zhenbo; Mishin, Oleg; Tao, N.R.;

    2015-01-01

    The microstructure, hardness and tensile properties of a modified 9Cr-1Mo steel processed by dynamic plastic deformation (DPD) to different strains (0.5 and 2.3) have been investigated in the as-deformed and annealed conditions. It is found that significant structural refinement and a high level...... of strength can be achieved by DPD to a strain of 2.3, and that the microstructure at this strain contains a large fraction of high angle boundaries. The ductility of the DPD processed steel is however low. Considerable structural coarsening of the deformed microstructure without pronounced recrystallization...

  16. Myocardial strain and strain rate in monitoring subclinical heart failure in asymptomatic long-term survivors of childhood cancer.

    NARCIS (Netherlands)

    Mavinkurve-Groothuis, A.M.C.; Groot-Loonen, J.J.; Marcus, K.A.; Bellersen, L.; Feuth, T.; Bokkerink, J.P.M.; Hoogerbrugge, P.M.; Korte, C.L. de; Kapusta, L.

    2010-01-01

    We studied the role of global myocardial strain and strain rate in monitoring subclinical heart failure in a large group of asymptomatic long-term survivors of childhood cancer. Global strain (rate) parameters of survivors were compared with those in healthy controls and were related to conventional

  17. Experimental Results of High Pressure and High Strain Rate Tantalum Flow Stress on Omega and NIF

    Science.gov (United States)

    Park, Hye-Sook; Arsenlis, A.; Barton, N.; Benedetti, L.; Huntington, C.; McNaney, J.; Orlikowski, D.; Prisbrey, S.; Remington, B.; Rudd, R.; Swift, D.; Weber, S.; Wehrenberg, C.; Comley, A.

    2015-11-01

    Understanding the high pressure, high strain rate plastic deformation dynamics of materials is an area of research of high interest to planetary formation dynamics, meteor impact dynamics, and inertial confinement fusion designs. Developing predictive theoretical and computational descriptions of such systems, however, has been a difficult undertaking. We have performed many experiments on Omega, LCLS and NIF to test Ta strength models at high pressures (~ up to 4 Mbar), high strain rates (~ 107 s-1) and high strains (>30%) under ramped compression conditions using Rayleigh-Taylor and Richtmyer-Meshkov instability properties. These experiments use plasma drive to ramp compress the sample to higher pressure without shock-melting. We also studied lattice level strength mechanisms under shocked compression using a diffraction-based technique. Our studies show that the strength mechanisms from macro to micro scales are different from the traditional strength model predictions and that they are loading path dependent. We will report the experimental results. Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA273.

  18. A study on rate sensitivity of elasto-plastic fracture toughness of TRIP steel evaluated by a small punch test

    Directory of Open Access Journals (Sweden)

    Shi L.

    2012-08-01

    Full Text Available TRIP steel indicates an excellent characteristic in energy absorption because of its high ductility and strength by strain-induced martensitic transformation (SIMT. Recently, some shock absorption members are being used for automotive industries. For good fuel consumption of the automobile, it would realize the weight reduction without decaying performance if TRIP steel can be applied to those members. It can be considered that the fracture toughness is an important factor to evaluate the performance. To evaluate fracture toughness locally at any point of a product of those members, small punch testing method is quite effective. In the present study, first, an impact small punch testing apparatus is established. In addition, elasto-plastic fracture toughness of TRIP steel under impact loading and its rate sensitivity tested at various deflection rates are challenged to evaluate.

  19. A study on rate sensitivity of elasto-plastic fracture toughness of TRIP steel evaluated by a small punch test

    Science.gov (United States)

    Iwamoto, T.; Hashimoto, S.-ya; Shi, L.

    2012-08-01

    TRIP steel indicates an excellent characteristic in energy absorption because of its high ductility and strength by strain-induced martensitic transformation (SIMT). Recently, some shock absorption members are being used for automotive industries. For good fuel consumption of the automobile, it would realize the weight reduction without decaying performance if TRIP steel can be applied to those members. It can be considered that the fracture toughness is an important factor to evaluate the performance. To evaluate fracture toughness locally at any point of a product of those members, small punch testing method is quite effective. In the present study, first, an impact small punch testing apparatus is established. In addition, elasto-plastic fracture toughness of TRIP steel under impact loading and its rate sensitivity tested at various deflection rates are challenged to evaluate.

  20. Measurement of fracture properties of concrete at high strain rates

    Science.gov (United States)

    Rey-De-Pedraza, V.; Cendón, D. A.; Sánchez-Gálvez, V.; Gálvez, F.

    2017-01-01

    An analysis of the spalling technique of concrete bars using the modified Hopkinson bar was carried out. A new experimental configuration is proposed adding some variations to previous works. An increased length for concrete specimens was chosen and finite-element analysis was used for designing a conic projectile to obtain a suitable triangular impulse wave. The aim of this initial work is to establish an experimental framework which allows a simple and direct analysis of concrete subjected to high strain rates. The efforts and configuration of these primary tests, as well as the selected geometry and dimensions for the different elements, have been focused to achieve a simple way of identifying the fracture position and so the tensile strength of tested specimens. This dynamic tensile strength can be easily compared with previous values published in literature giving an idea of the accuracy of the method and technique proposed and the possibility to extend it in a near future to obtain other mechanical properties such as the fracture energy. The tests were instrumented with strain gauges, accelerometers and high-speed camera in order to validate the results by different ways. Results of the dynamic tensile strength of the tested concrete are presented. This article is part of the themed issue 'Experimental testing and modelling of brittle materials at high strain rates'.

  1. Measurement of fracture properties of concrete at high strain rates.

    Science.gov (United States)

    Rey-De-Pedraza, V; Cendón, D A; Sánchez-Gálvez, V; Gálvez, F

    2017-01-28

    An analysis of the spalling technique of concrete bars using the modified Hopkinson bar was carried out. A new experimental configuration is proposed adding some variations to previous works. An increased length for concrete specimens was chosen and finite-element analysis was used for designing a conic projectile to obtain a suitable triangular impulse wave. The aim of this initial work is to establish an experimental framework which allows a simple and direct analysis of concrete subjected to high strain rates. The efforts and configuration of these primary tests, as well as the selected geometry and dimensions for the different elements, have been focused to achieve a simple way of identifying the fracture position and so the tensile strength of tested specimens. This dynamic tensile strength can be easily compared with previous values published in literature giving an idea of the accuracy of the method and technique proposed and the possibility to extend it in a near future to obtain other mechanical properties such as the fracture energy. The tests were instrumented with strain gauges, accelerometers and high-speed camera in order to validate the results by different ways. Results of the dynamic tensile strength of the tested concrete are presented.This article is part of the themed issue 'Experimental testing and modelling of brittle materials at high strain rates'.

  2. Two phase modeling of the influence of plastic strain on the magnetic and magnetostrictive behaviors of ferromagnetic materials

    Science.gov (United States)

    Hubert, Olivier; Lazreg, Said

    2017-02-01

    A growing interest of automotive industry in the use of high performance steels is observed. These materials are obtained thanks to complex manufacturing processes whose parameters fluctuations lead to strong variations of microstructure and mechanical properties. The on-line magnetic non-destructive monitoring is a relevant response to this problem but it requires fast models sensitive to different parameters of the forming process. The plastic deformation is one of these important parameters. Indeed, ferromagnetic materials are known to be sensitive to stress application and especially to plastic strains. In this paper, a macroscopic approach using the kinematic hardening is proposed to model this behavior, considering a plastic strained material as a two phase system. Relationship between kinematic hardening and residual stress is defined in this framework. Since stress fields are multiaxial, an uniaxial equivalent stress is calculated and introduced inside the so-called magneto-mechanical multidomain modeling to represent the effect of plastic strain. The modeling approach is complemented by many experiments involving magnetic and magnetostrictive measurements. They are carried out with or without applied stress, using a dual-phase steel deformed at different levels. The main interest of this material is that the mechanically hard phase, soft phase and the kinematic hardening can be clearly identified thanks to simple experiments. It is shown how this model can be extended to single phase materials.

  3. Crash simulation of hybrid structures considering the stress and strain rate dependent material behavior of thermoplastic materials

    Science.gov (United States)

    Hopmann, Ch.; Schöngart, M.; Weber, M.; Klein, J.

    2015-05-01

    Thermoplastic materials are more and more used as a light weight replacement for metal, especially in the automotive industry. Since these materials do not provide the mechanical properties, which are required to manufacture supporting elements like an auto body or a cross bearer, plastics are combined with metals in so called hybrid structures. Normally, the plastics components are joined to the metal structures using different technologies like welding or screwing. Very often, the hybrid structures are made of flat metal parts, which are stiffened by a reinforcement structure made of thermoplastic materials. The loads on these structures are very often impulsive, for example in the crash situation of an automobile. Due to the large stiffness variation of metal and thermoplastic materials, complex states of stress and very high local strain rates occur in the contact zone under impact conditions. Since the mechanical behavior of thermoplastic materials is highly dependent on these types of load, the crash failure of metal plastic hybrid parts is very complex. The problem is that the normally used strain rate dependent elastic/plastic material models are not capable to simulate the mechanical behavior of thermoplastic materials depended on the state of stress. As part of a research project, a method to simulate the mechanical behavior of hybrid structures under impact conditions is developed at the IKV. For this purpose, a specimen for the measurement of mechanical properties dependet on the state of stress and a method for the strain rate depended characterization of thermoplastic materials were developed. In the second step impact testing is performed. A hybrid structure made from a metal sheet and a reinforcement structure of a Polybutylenterephthalat Polycarbonate blend is tested under impact conditions. The measured stress and strain rate depended material data are used to simulate the mechanical behavior of the hybrid structure under highly dynamic load with

  4. Radial and longitudinal strain and strain rate assessed by speckle-tracking echocardiography in dogs with myxomatous mitral valve disease

    DEFF Research Database (Denmark)

    Zois, Nora Elisabeth; Tidholm, A.; Nägga, K.M.;

    2012-01-01

    Assessment of left ventricular (LV) function using conventional echocardiographic methods is difficult in mitral regurgitation (MR) owing to altered hemodynamic loading conditions. Newer methods such as speckle-tracking echocardiography (STE) provide assessment of LV strain (St) and strain rates ...

  5. Early detection of left ventricular dysfunction in asymptomatic diabetic patient using strain and strain rate echocardiographic imaging

    Directory of Open Access Journals (Sweden)

    Rania Gaber

    2014-03-01

    Conclusion: Type 2 diabetes mellitus deteriorate both LV systolic and diastolic performance. Strain and strain rate by tissue Doppler Imaging is superior to conventional Doppler in early detection and evaluation of systolic and diastolic dysfunction in type 2 diabetic patients.

  6. On the response of rubbers at high strain rates.

    Energy Technology Data Exchange (ETDEWEB)

    Niemczura, Johnathan Greenberg (University of Texas-Austin)

    2010-02-01

    In this report, we examine the propagation of tensile waves of finite deformation in rubbers through experiments and analysis. Attention is focused on the propagation of one-dimensional dispersive and shock waves in strips of latex and nitrile rubber. Tensile wave propagation experiments were conducted at high strain-rates by holding one end fixed and displacing the other end at a constant velocity. A high-speed video camera was used to monitor the motion and to determine the evolution of strain and particle velocity in the rubber strips. Analysis of the response through the theory of finite waves and quantitative matching between the experimental observations and analytical predictions was used to determine an appropriate instantaneous elastic response for the rubbers. This analysis also yields the tensile shock adiabat for rubber. Dispersive waves as well as shock waves are also observed in free-retraction experiments; these are used to quantify hysteretic effects in rubber.

  7. Single chain stochastic polymer modeling at high strain rates.

    Energy Technology Data Exchange (ETDEWEB)

    Harstad, E. N. (Eric N.); Harlow, Francis Harvey,; Schreyer, H. L.

    2001-01-01

    Our goal is to develop constitutive relations for the behavior of a solid polymer during high-strain-rate deformations. In contrast to the classic thermodynamic techniques for deriving stress-strain response in static (equilibrium) circumstances, we employ a statistical-mechanics approach, in which we evolve a probability distribution function (PDF) for the velocity fluctuations of the repeating units of the chain. We use a Langevin description for the dynamics of a single repeating unit and a Lioville equation to describe the variations of the PDF. Moments of the PDF give the conservation equations for a single polymer chain embedded in other similar chains. To extract single-chain analytical constitutive relations these equations have been solved for representative loading paths. By this process we discover that a measure of nonuniform chain link displacement serves this purpose very well. We then derive an evolution equation for the descriptor function, with the result being a history-dependent constitutive relation.

  8. A review of higher order strain gradient theories of plasticity: Origins, thermodynamics and connections with dislocation mechanics

    Indian Academy of Sciences (India)

    Suman Guha; Sandeep Sangal; Sumit Basu

    2015-06-01

    In this paper we review developments in higher order strain gradient theories. Several variants of these theories have been proposed in order to explain the effects of size on plastic properties that are manifest in several experiments with micron sized metallic structures. It is generally appreciated that the size effect arises from the storage of geometrically necessary dislocations (GNDs) over and above the statistically stored dislocations (SSDs) required for homogeneous deformations. We review developments that show that the GNDs result from the non-homogeneous nature of the deformation field. Though the connection between GNDs and strain gradients are established in the framework of single crystal plasticity, generalisations to polycrystal plasticity has been made. Strain gradient plasticity inherently involves an intrinsic length scale. In our review, we show, through a few illustrative problems, that conventional plasticity solutions can always be reduced to a scale independent form. The same problems are solved with a simple higher order strain gradient formulation to capture the experimentally observed size effects. However, higher order theories need to be thermodynamically consistent. It has recently been shown that only a few of the existing theories pass this test. We review a few that do. Higher order theories require higher order boundary conditions that enable us to model effects of dislocation storage at impermeable boundaries. But these additional boundary conditions also lead to unique conceptual issues that are not encountered in conventional theories. We review attempts at resolving these issues pertaining to higher order boundary conditions. Finally, we review the future of such theories, their relevance and experimental validation.

  9. Deformation nanotwins in coarse-grained aluminum alloy at ambient temperature and low strain rate

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Zhu; Li, Ning, E-mail: hslining@mail.hust.edu.cn; Jiang, Huawen; Liu, Lin

    2015-01-05

    In order to reveal the possible occurrence of deformation twins in coarse-grained aluminum/aluminum alloy at normal experimental conditions, a 5A02-O aluminum alloy with coarse grains was compressed quasi-statically to various plastic strains at ambient temperature, followed by high-resolution transmission electron analysis. The results revealed some long streaks produced by the thin plate-like structure with 2 atomic planes thick in the specimen undergoing a large strain, while under a relatively small plastic strain, the striped characteristics disappeared. The fast Fourier transform and theoretical analysis have shown that these long streaks are nanotwins, derived from the overlapping of stacking fault ribbons formed by Shockley partial dislocation on adjacent slip planes, which are triggered by the large plastic strain.

  10. The influence of acute unloading on left ventricular strain and strain rate by speckle tracking echocardiography in a porcine model.

    Science.gov (United States)

    Dahle, Geir Olav; Stangeland, Lodve; Moen, Christian Arvei; Salminen, Pirjo-Riitta; Haaverstad, Rune; Matre, Knut; Grong, Ketil

    2016-05-15

    Noninvasive measurements of myocardial strain and strain rate by speckle tracking echocardiography correlate to cardiac contractile state but also to load, which may weaken their value as indices of inotropy. In a porcine model, we investigated the influence of acute dynamic preload reductions on left ventricular strain and strain rate and their relation to the pressure-conductance catheter-derived preload recruitable stroke work (PRSW) and peak positive first derivative of left ventricular pressure (LV-dP/dtmax). Speckle tracking strain and strain rate in the longitudinal, circumferential, and radial directions were measured during acute dynamic reductions of end-diastolic volume during three different myocardial inotropic states. Both strain and strain rate were sensitive to unloading of the left ventricle (P speckle tracking echocardiography-derived strain rate is more robust to dynamic ventricular unloading than strain. Longitudinal and circumferential strain could not predict load-independent contractility. Strain rates, and especially in the radial direction, are good predictors of preload-independent inotropic markers derived from conductance catheter. Copyright © 2016 the American Physiological Society.

  11. Basic theories for strain localization analysis of porous media with rate dependent model

    Institute of Scientific and Technical Information of China (English)

    ZHANG Hongwu; QIN Jianmin

    2005-01-01

    This paper analyzes the interaction between two kinds of internal length scales when the rate dependent plasticity is introduced to a multiphase material model to study the dynamic strain localization phenomenon of saturated and partially saturated porous media. The stability analysis demonstrates that the enhanced porous media model preserves the well-posedness of the initial value problem for both axial and shear waves because an internal length scale parameter is introduced in the visco-plasticity model. On the other hand, the interaction between the length scale introduced by the rate dependent model and that naturally contained in the governing equations of fully and partially saturated model will take place. A basic method is presented to investigate the internal length scale of the multiphase porous media under the interaction of these two kinds of length scale parameters. Material stability analysis is carried out for a certain permeability from which the results of wave number domain with real wave speed are distinguished. A one dimensional example is given to illustrate the theoretical findings.

  12. Parametric analysis of plastic strain and force distribution in single pass metal spinning

    Energy Technology Data Exchange (ETDEWEB)

    Choudhary, Shashank, E-mail: shashankbit08@gmail.com, E-mail: mohantejesh93@gmail.com, E-mail: regalla@hyderabad.bits-pilani.ac.in, E-mail: ksuresh@hyderabad.bits-pilani.ac.in; Tejesh, Chiruvolu Mohan, E-mail: shashankbit08@gmail.com, E-mail: mohantejesh93@gmail.com, E-mail: regalla@hyderabad.bits-pilani.ac.in, E-mail: ksuresh@hyderabad.bits-pilani.ac.in; Regalla, Srinivasa Prakash, E-mail: shashankbit08@gmail.com, E-mail: mohantejesh93@gmail.com, E-mail: regalla@hyderabad.bits-pilani.ac.in, E-mail: ksuresh@hyderabad.bits-pilani.ac.in; Suresh, Kurra, E-mail: shashankbit08@gmail.com, E-mail: mohantejesh93@gmail.com, E-mail: regalla@hyderabad.bits-pilani.ac.in, E-mail: ksuresh@hyderabad.bits-pilani.ac.in [Department of Mechanical Engineering, BITS-Pilani, Hyderabad Campus, Shamirpet, Hyderabad, 500078, Andhra Pradesh (India)

    2013-12-16

    Metal spinning also known as spin forming is one of the sheet metal working processes by which an axis-symmetric part can be formed from a flat sheet metal blank. Parts are produced by pressing a blunt edged tool or roller on to the blank which in turn is mounted on a rotating mandrel. This paper discusses about the setting up a 3-D finite element simulation of single pass metal spinning in LS-Dyna. Four parameters were considered namely blank thickness, roller nose radius, feed ratio and mandrel speed and the variation in forces and plastic strain were analysed using the full-factorial design of experiments (DOE) method of simulation experiments. For some of these DOE runs, physical experiments on extra deep drawing (EDD) sheet metal were carried out using En31 tool on a lathe machine. Simulation results are able to predict the zone of unsafe thinning in the sheet and high forming forces that are hint to the necessity for less-expensive and semi-automated machine tools to help the household and small scale spinning workers widely prevalent in India.

  13. Material properties of the heel fat pad across strain rates.

    Science.gov (United States)

    Grigoriadis, Grigoris; Newell, Nicolas; Carpanen, Diagarajen; Christou, Alexandros; Bull, Anthony M J; Masouros, Spyros D

    2017-01-01

    The complex structural and material behaviour of the human heel fat pad determines the transmission of plantar loading to the lower limb across a wide range of loading scenarios; from locomotion to injurious incidents. The aim of this study was to quantify the hyper-viscoelastic material properties of the human heel fat pad across strains and strain rates. An inverse finite element (FE) optimisation algorithm was developed and used, in conjunction with quasi-static and dynamic tests performed to five cadaveric heel specimens, to derive specimen-specific and mean hyper-viscoelastic material models able to predict accurately the response of the tissue at compressive loading of strain rates up to 150s(-1). The mean behaviour was expressed by the quasi-linear viscoelastic (QLV) material formulation, combining the Yeoh material model (C10=0.1MPa, C30=7MPa, K=2GPa) and Prony׳s terms (A1=0.06, A2=0.77, A3=0.02 for τ1=1ms, τ2=10ms, τ3=10s). These new data help to understand better the functional anatomy and pathophysiology of the foot and ankle, develop biomimetic materials for tissue reconstruction, design of shoe, insole, and foot and ankle orthoses, and improve the predictive ability of computational models of the foot and ankle used to simulate daily activities or predict injuries at high rate injurious incidents such as road traffic accidents and underbody blast. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

  14. Strain rate dependent behaviors of a hot isotropically processed Ti-6Al-4V: Mechanisms and material model

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Xiaohan; Ren, Mingfa; Bu, Fanzi; Chen, Guoqing; Li, Gang [Dalian University of Technology, Dalian (China); Li, Tong [Queensland University of Technology, Brisbane (Australia)

    2016-02-15

    Split-Hopkinson pressure bar (SHPB) was adopted to study the dynamic response of a specifically designed Hot isotropically processed (HIP) Casting Titanium alloy (Ti-6Al-4V). The strain-stress curves were obtained in a range of strain rate (10{sup -3}⁓2.6x10{sup 3}/s) to study the constitutive relationships and the Johnson-Cook model is developed to describe this dynamic constitutive law. It can be found that the static microstructure of this specific HIP casting Ti-6Al-4V is lamellar structure. When the loading increases (strain rate higher than 10{sup 3}/s), this lamellar structure changes to basket weave structure, which further changes the mechanical strength and plasticity.

  15. Phase field simulations of plastic strain-induced phase transformations under high pressure and large shear

    Science.gov (United States)

    Javanbakht, Mahdi; Levitas, Valery I.

    2016-12-01

    Pressure and shear strain-induced phase transformations (PTs) in a nanograined bicrystal at the evolving dislocations pile-up have been studied utilizing a phase field approach (PFA). The complete system of PFA equations for coupled martensitic PT, dislocation evolution, and mechanics at large strains is presented and solved using the finite element method (FEM). The nucleation pressure for the high-pressure phase (HPP) under hydrostatic conditions near a single dislocation was determined to be 15.9 GPa. Under shear, a dislocation pile-up that appears in the left grain creates strong stress concentration near its tip and significantly increases the local thermodynamic driving force for PT, which causes nucleation of HPP even at zero pressure. At pressures of 1.59 and 5 GPa and shear, a major part of a grain transforms to HPP. When dislocations are considered in the transforming grain as well, they relax stresses and lead to a slightly smaller stationary HPP region than without dislocations. However, they strongly suppress nucleation of HPP and require larger shear. Unexpectedly, the stationary HPP morphology is governed by the simplest thermodynamic equilibrium conditions, which do not contain contributions from plasticity and surface energy. These equilibrium conditions are fulfilled either for the majority of points of phase interfaces or (approximately) in terms of stresses averaged over the HPP region or for the entire grain, despite the strong heterogeneity of stress fields. The major part of the driving force for PT in the stationary state is due to deviatoric stresses rather than pressure. While the least number of dislocations in a pile-up to nucleate HPP linearly decreases with increasing applied pressure, the least corresponding shear strain depends on pressure nonmonotonously. Surprisingly, the ratio of kinetic coefficients for PT and dislocations affect the stationary solution and the nanostructure. Consequently, there are multiple stationary solutions

  16. Measurement of strain and strain rate in embryonic chick heart using spectral domain optical coherence tomography

    Science.gov (United States)

    Dou, Shidan; Suo, Yanyan; Liang, Chengbo; Wang, Yi; Zhao, Yuqian; Liu, Jian; Xu, Tao; Wang, Ruikang; Ma, Zhenhe

    2016-03-01

    It is important to measure embryonic heart myocardial wall strain and strain rate for understanding the mechanisms of embryonic heart development. Optical coherence tomography (OCT) can provide depth resolved images with high spatial and temporal resolution, which makes it have the potential to reveal the complex myocardial activity in the early stage embryonic heart. We develop a novel method to measure strain in embryonic chick heart based on spectral domain OCT images and subsequent image processing. We perform 4D(x,y,z,t) scanning on the outflow tract (OFT) of chick embryonic hearts in HH18 stage (~3 days of incubation). Only one image sequence acquired at the special position is selected based on the Doppler blood flow information where the probe beam penetrates through the OFT perpendicularly. For each image of the selected sequence, the cross-section of the myocardial wall can be approximated as an annulus. The OFT is segmented with a semi-automatic boundary detection algorithm, thus the area and mean circumference of the annular myocardial wall can be achieved. The myocardial wall thickness was calculated using the area divided by the mean circumference, and then the strain was obtained. The results demonstrate that OCT can be a useful tool to describe the biomechanical characteristics of the embryonic heart.

  17. Adiabatic Shear Band Formation in Intermetallic WHA at High Strain Rates and Elevated Temperatures

    Science.gov (United States)

    Duprey, K. E.; Clifton, R. J.; Griffo, A.; German, R. M.

    1997-07-01

    A novel tungsten-based composite is being developed at The Pennsylvania State University to enhance shear banding by introducing a strong thermo-plastic instability. This liquid phase sintered composite consists of tungsten grains embedded in an intermetallic alloy matrix which has the property that its flow stress increases with increasing temperature up to a critical temperature at which rapid thermal softening begins. Pressure-shear plate impact experiments are being used to subject thin plates of this composite to shearing at strain rates of 10^5 s-1 to 10^6 s-1 at pressures of 6 - 8 GPa, and temperatures up to 650 ^o C. The experiments, combined with computer simulation, are being conducted to determine the effects of the thermal properties of the matrix on the initiation and propagation of adiabatic shear bands.

  18. Numerical analysis of high strain rate failure of electro-magnetically loaded steel sheets

    Directory of Open Access Journals (Sweden)

    Erice Borja

    2015-01-01

    Full Text Available Electro-magnetic forces provide a potentially power full means in designing dynamic experiments with active control of the loading conditions. This article deals with the development of computational models to simulate the thermo-mechanical response of electro-magnetically loaded metallic structures. The model assumes linear electromagnetic constitutive equations and time-independent electric induction to estimate the Joule heating and the Lorentz forces. The latter are then taken into account when evaluating stress equilibrium. A thermo-visco-plastic model with Johnson-Cook type of temperature and strain rate dependence and combined Swift-Voce hardening is used to evaluate the material's thermo-mechanical response. As a first application, the model is used to analyse the effect of electro-magnetic loading on the ductility of advanced high strength steels.

  19. Molecular dynamics simulation of materials response to high strain-rate loading

    Energy Technology Data Exchange (ETDEWEB)

    Belak, J

    1999-07-22

    A molecular dynamics (MD) analysis of conservation of momentum through a shock front is presented. The MD model uses a non-traditional boundary condition that allows simulation in the reference frame of the shock front. Higher order terms proportional to gradients in the density are shown to be non-negligible at the shock front. The simulation is used to study the sequence of thermodynamic states during shock loading. Melting is observed in the simulations, though above the thermodynamic melt curve as is common in homogeneous simulations of melting. High strain-rate tensile loading is applied to the growth of nanoscale voids in copper. Void growth is found to occur by plasticity mechanisms with dislocations emerging from the void surface. [molecular dynamics, shock loading, conservation of momentum, shock melting, void growth

  20. Atrial Strain and Strain Rate: A Novel Method for the Evaluation of Atrial Stunning

    Science.gov (United States)

    Ozkan, Hakan; Binici, Suleyman; Tenekecioglu, Erhan; Ari, Hasan; Bozat, Tahsin

    2016-01-01

    Background Atrial fibrillation (AF) is the most common arrhythmia seen in adults. Atrial stunning is defined as the temporary mechanical dysfunction of the atrial appendage developing after AF has returned to sinus rhythm (SR). Objectives We aimed to evaluate atrial contractile functions by strain and strain rate in patients with AF, following pharmacological and electrical cardioversion and to compare it with conventional methods. Methods This study included 41 patients with persistent AF and 35 age-matched control cases with SR. All the AF patients included in the study had transthoracic and transesophageal echocardiography performed before and after. Septum (SEPsSR), left atrium (LAsSR) and right atrium peak systolic strain rate (RAsSR) were defined as the maximum negative value during atrial contraction and septum (SEPε), left atrium (LAε) and right atrium peak systolic strain (RAε) was defined as the percentage of change. Parameters of two groups were compared. Results In the AF group, 1st hour and 24th hour LAε, RAε, SEPε, LAsSR, RAsSR, SEPsSR found to be significantly lower than in the control group (LAε: 2.61%±0.13, 3.06%±0.19 vs 6.45%±0.27, p<0.0001; RAε: 4.03%±0.38, 4.50%±0.47 vs 10.12%±0.64, p<0.0001; SEPε: 3.0%±0.22, 3.19%±0.15 vs 6.23%±0.49, p<0.0001; LAsSR: 0.61±0.04s-1, 0.75±0.04s-1 vs 1.35±0.04s-1, p<0.0001; RAsSR: 1.13±0.06s-1, 1.23±0.07s-1 vs 2.10±0.08s- 1, p<0.0001; SEPsSR: 0.76±0.04s- 1, 0.78±0.04s- 1 vs 1.42±0.06 s- 1, p<0.0001). Conclusion Atrial strain and strain rate parameters are superior to conventional echocardiographic parameters for the evaluation of atrial stunning in AF cases where SR has been achieved. PMID:27627221

  1. Stress-strain curves of aluminum nanowires: Fluctuations in the plastic regime and absence of hardening

    Science.gov (United States)

    Pastor-Abia, L.; Caturla, M. J.; Sanfabián, E.; Chiappe, G.; Louis, E.

    2008-10-01

    The engineering stress-strain curves of aluminum nanowires have been investigated by means of molecular dynamics. Nanowires were stretched at constant strain rate and at a temperature of 4.2 K. Atoms at fixed positions with velocities randomly distributed according to Maxwell distribution were taken as initial conditions. Averaging over at least 1500 realizations allows the conclusion that, beyond the yield point, the system does not harden, in line with experimental results for larger nanowires of gold measured at room temperature. Fluctuations of the heat exchanged in the nonlinear regime have been investigated by analyzing around 1.5 million data. The results indicate the presence of non-Gaussian tails in the heat probability distribution.

  2. The effect of an acute bout of resistance exercise on carotid artery strain and strain rate.

    Science.gov (United States)

    Black, Jane M; Stöhr, Eric J; Stone, Keeron; Pugh, Christopher J A; Stembridge, Mike; Shave, Rob; Esformes, Joseph I

    2016-09-01

    Arterial wall mechanics likely play an integral role in arterial responses to acute physiological stress. Therefore, this study aimed to determine the impact of low and moderate intensity double-leg press exercise on common carotid artery (CCA) wall mechanics using 2D vascular strain imaging. Short-axis CCA ultrasound images were collected in 15 healthy men (age: 21 ± 3 years; stature: 176.5 ± 6.2 cm; body mass; 80.6 ± 15.3 kg) before, during, and immediately after short-duration isometric double-leg press exercise at 30% and 60% of participants' one-repetition maximum (1RM: 317 ± 72 kg). Images were analyzed for peak circumferential strain (PCS), peak systolic and diastolic strain rate (S-SR and D-SR), and arterial diameter. Heart rate (HR), systolic and diastolic blood pressure (SBP and DBP) were simultaneously assessed and arterial stiffness indices were calculated post hoc. A two-way repeated measures ANOVA revealed that during isometric contraction, PCS and S-SR decreased significantly (P exercise (P exercise is therefore associated with similar transient changes in CCA wall mechanics at low and moderate intensities. CCA wall mechanics likely provide additional insight into localized intrinsic vascular wall properties beyond current measures of arterial stiffness.

  3. Twin Interactions in Pure Ti Under High Strain Rate Compression

    Science.gov (United States)

    Zhou, Ping; Xiao, Dawu; Jiang, Chunli; Sang, Ge; Zou, Dongli

    2017-01-01

    Twin interactions associated with {11 overline{2} 1} (E2) twins in titanium deformed by high strain rate ( 2600 s-1) compression were studied using electron backscatter diffraction technique. Three types of twins, {10 overline{1} 2} (E1), {11 overline{2} 2} (C1), and {11 overline{2} 4} (C3), were observed to interact with the preformed E2 twins in four parent grains. The E1 variants nucleated at twin boundaries of some E2 variants. And the C3 twins were originated from the intersection of C1 and E2. The selection of twin variant was investigated by the Schmid factors (SFs) and the twinning shear displacement gradient tensors (DGTs) calculations. The results show that twin variants that did not follow the Schmid law were more frequently observed under high strain rate deformation than quasi-static deformation. Among these low-SF active variants, 73 pct (8 out of 11) can be interpreted by DGT. Besides, 26 variants that have SF values close to or higher than their active counterparts were absent. Factors that may affect the twin variant selections were discussed.

  4. Influence of strain rate on fracture behavior of poly(methyl methacrylate)

    Institute of Scientific and Technical Information of China (English)

    赵荣国; 陈朝中

    2008-01-01

    The effect of strain rate on fracture behavior of poly(methyl methacrylate) was investigated.The uniaxial tensile rupture tests for the poly(methyl methacrylate) samples were carried out at different strain rates at ambient temperature.It is found that the elastic modulus of the material increases with increasing strain rate,while the elongation is reversal with strain rate.Simultaneously,there exists a critical strain rate within which the stress-strain curves overlap one another,and beyond which the curves depart from each other.The amount of energy added to the system due to work done by the imposed load was calculated,and the strain energy stored in the material at each strain rate was calculated by the current stress integral with respect to strain.The complementary strain energy,which is the difference between the work and the strain energy,was obtained and was considered to supply the surface energy to create a new crack surface in the polymeric material.It is found that the work done by the imposed load,which is needed for the fracture of poly(methyl methacrylate) sample,decreases with increasing strain rate,and the strain energy decreases with strain rate as well,which demonstrates that the polymeric material at high strain rate is easier to fracture than that at low strain rate.As the strain rate increases,the fracture mode changes from ductile,semi-ductile to brittle mode.The complementary strain energy almost sustains a constant at any strain rate.The density of surface energy,which characterizes the energy per unit area needed for creating crack surface,is a strain rate-independent material constant.

  5. Plasticity of Performance Curves Can Buffer Reaction Rates from Body Temperature Variation in Active Endotherms

    Directory of Open Access Journals (Sweden)

    Frank Seebacher

    2017-08-01

    Full Text Available Endotherms regulate their core body temperature by adjusting metabolic heat production and insulation. Endothermic body temperatures are therefore relatively stable compared to external temperatures. The thermal sensitivity of biochemical reaction rates is thought to have co-evolved with body temperature regulation so that optimal reaction rates occur at the regulated body temperature. However, recent data show that core body temperatures even of non-torpid endotherms fluctuate considerably. Additionally, peripheral temperatures can be considerably lower and more variable than core body temperatures. Here we discuss whether published data support the hypothesis that thermal performance curves of physiological reaction rates are plastic so that performance is maintained despite variable body temperatures within active (non-torpid endotherms, and we explore mechanisms that confer plasticity. There is evidence that thermal performance curves in tissues that experience thermal fluctuations can be plastic, although this question remains relatively unexplored for endotherms. Mechanisms that alter thermal responses locally at the tissue level include transient potential receptor ion channels (TRPV and TRPM and the AMP-activated protein kinase (AMPK both of which can influence metabolism and energy expenditure. Additionally, the thermal sensitivity of processes that cause post-transcriptional RNA degradation can promote the relative expression of cold-responsive genes. Endotherms can respond to environmental fluctuations similarly to ectotherms, and thermal plasticity complements core body temperature regulation to increase whole-organism performance. Thermal plasticity is ancestral to endothermic thermoregulation, but it has not lost its selective advantage so that modern endotherms are a physiological composite of ancestral ectothermic and derived endothermic traits.

  6. Predator-induced phenotypic plasticity in metabolism and rate of growth: rapid adaptation to a novel environment.

    Science.gov (United States)

    Handelsman, Corey A; Broder, E Dale; Dalton, Christopher M; Ruell, Emily W; Myrick, Christopher A; Reznick, David N; Ghalambor, Cameron K

    2013-12-01

    Novel environments often impose directional selection for a new phenotypic optimum. Novel environments, however, can also change the distribution of phenotypes exposed to selection by inducing phenotypic plasticity. Plasticity can produce phenotypes that either align with or oppose the direction of selection. When plasticity and selection are parallel, plasticity is considered adaptive because it provides a better pairing between the phenotype and the environment. If the plastic response is incomplete and falls short of producing the optimum phenotype, synergistic selection can lead to genetic divergence and bring the phenotype closer to the optimum. In contrast, non-adaptive plasticity should increase the strength of selection, because phenotypes will be further from the local optimum, requiring antagonistic selection to overcome the phenotype-environment mismatch and facilitate adaptive divergence. We test these ideas by documenting predator-induced plasticity for resting metabolic rate and growth rate in populations of the Trinidadian guppy (Poecilia reticulata) adapted to high and low predation. We find reduced metabolic rates and growth rates when cues from a predator are present during development, a pattern suggestive of adaptive and non-adaptive plasticity, respectively. When we compared populations recently transplanted from a high-predation environment into four streams lacking predators, we found evidence for rapid adaptive evolution both in metabolism and growth rate. We discuss the implications for predicting how traits will respond to selection, depending on the type of plasticity they exhibit.

  7. RIGID-PLASTIC/RIGID-VISCOPLASTIC FEM BASED ON LINEAR PROGRAMMING-THEORETICAL MODELING AND APPLICATION FOR PLANE-STRAIN PROBLEMS

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    A new rigid-plastic/rigid-viscoplastic (RP/RVP) FEM based on linear programming (LP) for plane-strain metal forming simulation is proposed. Compared with the traditional RP/RVP FEM based on iteration solution, it has some remarkable advantages, such as it's free of convergence problem and its convenience in contact, incompressibility constraint and rigid zone treatment. Two solution examples are provided to validate its accuracy and efficiency.

  8. The Microstructural Evolution and Mechanical Properties of Zr-Based Metallic Glass under Different Strain Rate Compressions

    Directory of Open Access Journals (Sweden)

    Tao-Hsing Chen

    2015-04-01

    Full Text Available In this study, the high strain rate deformation behavior and the microstructure evolution of Zr-Cu-Al-Ni metallic glasses under various strain rates were investigated. The influence of strain and strain rate on the mechanical properties and fracture behavior, as well as microstructural properties was also investigated. Before mechanical testing, the structure and thermal stability of the Zr-Cu-Al-Ni metallic glasses were studied with X-ray diffraction (XRD and differential scanning calorimeter. The mechanical property experiments and microstructural observations of Zr-Cu-Al-Ni metallic glasses under different strain rates ranging from 10−3 to 5.1 × 103 s−1 and at temperatures of 25 °C were investigated using compressive split-Hopkinson bar (SHPB and an MTS tester. An in situ transmission electron microscope (TEM nanoindenter was used to carry out compression tests and investigate the deformation behavior arising at nanopillars of the Zr-based metallic glass. The formation and interaction of shear band during the plastic deformation were investigated. Moreover, it was clearly apparent that the mechanical strength and ductility could be enhanced by impeding the penetration of shear bands with reinforced particles.

  9. Effect of Strain Rate on Compression Behavior of Vinyl Ester Resin Casting

    Institute of Scientific and Technical Information of China (English)

    XIONG Tao; YANG Bin; XIONG Jie; XU Xian-jian; ZHOU Kai; MAO Ming-zhong

    2006-01-01

    Quasi-static and high strain rate compressive experiments on vinyl ester casting were carried out by means of MTS (Material Test System) and Hopkinson bar. The behaviors of the compressed unstable and fracture of the resin casting at different strain rates were investigated. The results indicate that the response behavior of the resin casting is controlled by different mechanisms at different strain rate, and some mechanical properties of vinyl ester casting are ratedependent: the casting are destroyed in toughness model under strain rate 3.3 × 10-4 ~ 6.6 × 10-3/s, while the casting are destroyed in brittleness model under strain rate 950~5800/s. The yield stress, yield strain energy density are all increased with the increasing strain rates at quasi-static as well as at high strain rates. What is interesting is that the yield strain decreased with the strain rates increasing at quasi-static while increased at high strain rates. It is considered that the casting occurred forcing high elastic deformation at high strain rates. The damage of the specimens is mainly controlled by axial stress before unstable deformation, while mainly controlled by shear stress after unstable deformation, and then developed to fracture finally. This progress is rate-dependent: the development of the cracks inside the castings increased with the strain rate increasing.

  10. Atrial strain rate is a sensitive measure of alterations in atrial phasic function in healthy ageing.

    Science.gov (United States)

    Boyd, Anita C; Richards, David A B; Marwick, Thomas; Thomas, Liza

    2011-09-01

    Strain and strain rate measure local deformation of the myocardium and have been used to evaluate phasic atrial function in various disease states. The aim of this study was to define normal values for tissue Doppler-derived atrial strain measurements and examine age-related changes by decade in healthy individuals. Transthoracic echocardiograms were performed on 188 healthy subjects. Tissue Doppler-derived strain and strain rate were measured from the apical four and two-chamber views of the left atrium, and global values were calculated as the mean of all segments. Measurements included peak systolic strain, systolic strain rate, early and late diastolic strain rate. Phasic left atrial volumes and fractions were calculated. Mitral inflow and tissue Doppler imaging were employed to estimate left ventricular diastolic function. A significant reduction in global systolic strain was observed from decade 6. Alterations in atrial strain rate were apparent from decade 5; systolic strain rate and early diastolic strain rate decreased, while late diastolic strain rate increased significantly. Changes in phasic atrial volume and function occurred in conjunction with age-related changes in left ventricular diastolic function. Importantly, age-related changes in global atrial systolic strain rate and early diastolic strain rate occurred a decade before corresponding changes in atrial phasic volume parameters. Atrial strain and strain rate can be used to quantify atrial phasic function and appear to be altered before traditional parameters with ageing. Strain analysis may therefore be more sensitive in detecting subclinical atrial dysfunction with alterations in strain rate parameters observed before traditional parameters.

  11. Plastic surgeons’ self-reported operative infection rates at a Canadian academic hospital

    OpenAIRE

    Ng, Wendy KY; Kaur, Manraj Nirmal; Thoma, Achilleas

    2014-01-01

    The significant morbidity associated with surgical site infections, in addition to increased hospital stays and health care resource utilization, has garnered much attention, especially in the era of cost-conscious health care systems and third-party payers. Although previous studies have investigated hospital-acquired infection rates across all surgical subspecialities, none have focused specifically on plastic surgery procedures. This retrospective study examined surgical site infection dat...

  12. Analysis of field usage failure rate data for plastic encapsulated solid state devices

    Science.gov (United States)

    1981-01-01

    Survey and questionnaire techniques were used to gather data from users and manufacturers on the failure rates in the field of plastic encapsulated semiconductors. It was found that such solid state devices are being successfully used by commercial companies which impose certain screening and qualification procedures. The reliability of these semiconductors is now adequate to support their consideration in NASA systems, particularly in low cost systems. The cost of performing necessary screening for NASA applications was assessed.

  13. Properties of heterogeneous energetic materials under high strain, high strain rate deformation

    Science.gov (United States)

    Cai, Jing

    Heterogeneous energetic materials have many applications. Their dynamic behavior and microstructural evolution upon plastic deformation have remained not fully understood. The following heterogeneous materials were investigated in the this study: the pure PTFE (usually a mixture of crystalline and amorphous phases), PTFE-Sn, PTFE-Al, PTFE-Al-W, and carbon fibers filled Al alloy. Sample manufacturing processes involving ball milling and Cold Isostatic Pressing were employed. Quasi-static and Hopkinson bar tests were carried out to obtain the compressive strengths of composites. The Conventional Thick-walled Cylinder (TWC) method and newly developed small-scale Hopkinson bar based TWC experiments were conducted to investigate single shear bands and their assembly. Conventional and "soft" drop-weight tests were performed to examine the mechanical properties and the initiation of chemical reactions. Scanning Electron Microscopy was used to detect the details of the microstructures and failure mechanisms of heterogeneous materials. New features in the dynamic behavior of heterogeneous materials were observed. They include the following: (1) Strain softening, instead of thermal softening, is the main mechanism in the initiation of shear bands in explosively driven TWC tests of solid PTFE. (2) Cold isostatically pressed PTFE-Sn samples were more stable with respect to shear localization than solid PTFE. (3) The dynamic collapse of solid PTFE-Al samples with different particle sizes was accomplished with the shear localization bands and cracks. (4) Force chains in the fine W and Al particles were attributed to the high strength of the porous PTFE-Al-W composite containing fine W particles in comparison with composites with coarse W particles. (5) Debonding of metal particles from the PTFE matrix and the fracture of the matrix were identified to be two major mechanisms for the failure of the PTFE-Al-W composites. (6) The formation of PTFE nano-fibers during high strain flow

  14. High strain rate superplastic aluminium alloys: the way forward?

    Energy Technology Data Exchange (ETDEWEB)

    Grimes, R.; Dashwood, R.J.; Flower, H.M. [Imperial Coll. of Science, Technology and Medicine, London (United Kingdom). Dept. of Materials

    2001-07-01

    The technical and commercial barriers to the development and successful exploitation of a high strain rate superplastically deformable aluminium alloy for use in the automotive industry are considered in this paper. Batch processing routes, such as mechanical alloying or equal channel angular extrusion, employed to deliver appropriate chemistry and structure, are inherently costly and unlikely to deliver either the quantity or the size of strip required commercially. There is evidence that there is still scope for development of conventional casting and rolling routes, but a particulate casting route combined with roll consolidation offers the prospect of a commercially viable Al-Mg-Zr product. The use of alloying additions, including zirconium, is also discussed and comparative costs are presented: on this basis the use of scandium appears economically prohibitive. (orig.)

  15. Potential pitfalls of strain rate imaging: angle dependency

    Science.gov (United States)

    Castro, P. L.; Greenberg, N. L.; Drinko, J.; Garcia, M. J.; Thomas, J. D.

    2000-01-01

    Strain Rate Imaging (SRI) is a new echocardiographic technique that allows for the real-time determination of myocardial SR, which may be used for the early and accurate detection of coronary artery disease. We sought to study whether SR is affected by scan line alignment in a computer simulation and an in vivo experiment. Through the computer simulation and the in vivo experiment we generated and validated safe scanning sectors within the ultrasound scan sector and showed that while SRI will be an extremely valuable tool in detecting coronary artery disease there are potential pitfalls for the unwary clinician. Only after accounting for these affects due to angle dependency, can clinicians utilize SRI's potential as a valuable tool in detecting coronary artery disease.

  16. DILATANCY BEHAVIOR IN CONSTANT STRAIN RATE CONSOLIDATION TEST

    Directory of Open Access Journals (Sweden)

    Berty Sompie

    2006-01-01

    Full Text Available Subjected to remolded young clay, this paper shows that a lot of time dependent behavior in the standard consolidation (SC and constant strain rate consolidation (CSRC tests is represented systematically by a simple assumption concerning the time dependency of dilatancy. In the SC test, at the first stage of each loading step little dilatancy takes place and dilatancy begins to occur several minutes after step loading. In CSRC test, some time period after the stress state has entered the normally consolidated region, dilatancy tends to occur rapidly with the increase in stress ratio. Since most of dilatancy has taken place at the earlier stage of consolidation, little dilatancy occurs at the latter stage of CSRC process. This tendency makes the specimen stiffer with the passage of time, and makes the vertical pressure and pore pressure increase substantially at the last stage of CSRC process. Consideration to such behavior may be effective to correctly interpret the result of CSRC test.

  17. Material deformation dynamics at ultrahigh pressures and strain rates

    Science.gov (United States)

    Remington, B. A.; Park, H. S.; Maddox, B. R.; May, M. J.; Pollaine, S. M.; Prisbrey, S. T.; Rudd, R. E.; Hawreliak, J. A.; Perry, T. S.; Comley, A. J.; Wark, J. S.; Meyers, M. A.

    2010-11-01

    Solid-state dynamics experiments at extreme pressures, up to 10 Mbar, and strain rates (1.e6 -1.e8 1/s) are being developed for the NIF laser. The experimental methods are being developed on the Omega laser facility. VISAR measurements establish the ramped, high-pressure conditions. Recovery experiments offer a look at the residual microstructure. Dynamic diffraction measurements allow phase, shear stress (strength), and possibly twin volume fraction and dislocation density to be inferred. Constitutive models for material strength at these conditions by comparing 2D simulations with experiments measuring the Rayleigh-Taylor instability evolution in solid-state samples of vanadium and tantalum. The material deformation likely falls into the phonon drag regime. We estimate of the (microscopic) phonon drag coefficient, by relating to the (macroscopic) effective lattice viscosity.

  18. Deviatoric constitutive model: domain of strain rate validity

    Energy Technology Data Exchange (ETDEWEB)

    Zocher, Marvin A [Los Alamos National Laboratory

    2009-01-01

    A case is made for using an enhanced methodology in determining the parameters that appear in a deviatoric constitutive model. Predictability rests on our ability to solve a properly posed initial boundary value problem (IBVP), which incorporates an accurate reflection of material constitutive behavior. That reflection is provided through the constitutive model. Moreover, the constitutive model is required for mathematical closure of the IBVP. Common practice in the shock physics community is to divide the Cauchy tensor into spherical and deviatoric parts, and to develop separate models for spherical and deviatoric constitutive response. Our focus shall be on the Cauchy deviator and deviatoric constitutive behavior. Discussions related to the spherical part of the Cauchy tensor are reserved for another time. A number of deviatoric constitutive models have been developed for utilization in the solution of IBVPs that are of interest to those working in the field of shock physics, e.g. All of these models are phenomenological and contain a number of parameters that must be determined in light of experimental data. The methodology employed in determining these parameters dictates the loading regime over which the model can be expected to be accurate. The focus of this paper is the methodology employed in determining model parameters and the consequences of that methodology as it relates to the domain of strain rate validity. We shall begin by describing the methodology that is typically employed. We shall discuss limitations imposed upon predictive capability by the typically employed methodology. We shall propose a modification to the typically employed methodology that significantly extends the domain of strain rate validity.

  19. The high strain-rate behaviour of selected tissue analogues.

    Science.gov (United States)

    Appleby-Thomas, G J; Hazell, P J; Sheldon, R P; Stennett, C; Hameed, A; Wilgeroth, J M

    2014-05-01

    The high strain-rate response of four readily available tissue simulants has been investigated via plate-impact experiments. Comparison of the shock response of gelatin, ballistic soap (both sub-dermal tissue simulants), lard (adipose layers) and Sylgard(®) (a potential brain simulant) allowed interrogation of the applicability of such monolithic tissue surrogates in the ballistic regime. The gelatin and lard exhibited classic linear Hugoniot equations-of-state in the US-uP plane; while for the ballistic soap and Sylgard(®) a polymer-like non-linear response was observed. In the P/σX-v/v0 plane there was evidence of separation of the simulant materials into distinct groups, suggesting that a single tissue simulant is inadequate to ensure a high-fidelity description of the high strain-rate response of complex mammalian tissue. Gelatin appeared to behave broadly hydrodynamically, while soap, lard and Sylgard(®) were observed to strengthen in a material-dependent manner under specific loading conditions at elevated shock loading pressures/stresses. This strengthening behaviour was tentatively attributed to a further polymeric-like response in the form of a re-arrangement of the molecular chains under loading (a steric effect). In addition, investigation of lateral stress data from the literature showed evidence of operation of a material-independent strengthening mechanism when these materials were stressed above 2.5-3.0GPa, tentatively linked to the generically polymeric-like underlying microstructure of the simulants under consideration.

  20. Behavior of Unsaturated Clayey Soils at High Strain Rates

    Science.gov (United States)

    1992-10-01

    DISTRIBUTION .............................. 89 4.4 SOIL PLASTICITY CHARACTERISTICS ...................... 93 4.5 CATION EXCHANGE CAPACITY...that the results on the soil stock are more reliable and, thus, give a more representative percentage of clay sizes in the soil stock. 4.4 SOIL ... PLASTICITY CHARACTERISTICS Two specimen of the cleaned soil stock were used to perform a two series of Atterberg Limits determinations. For this purpose

  1. Constitutive modelling and identification of parameters of the plastic strain-induced martensitic transformation in 316L stainless steel at cryogenic temperatures

    CERN Document Server

    Garion, C; Sgobba, Stefano

    2006-01-01

    The present paper is focused on constitutive modelling and identification of parameters of the relevant model of plastic strain- induced martensitic transformation in austenitic stainless steels at low temperatures. The model used to describe the FCCrightward arrow BCC phase transformation in austenitic stainless steels is based on the assumption of linearization of the most intensive part of the transformation curve. The kinetics of phase transformation is described by three parameters: transformation threshold (p/sub xi/), slope (A) and saturation level (xi/sub L/). It is assumed that the phase transformation is driven by the accumulated plastic strain p. In addition, the intensity of plastic deformation is strongly coupled to the phase transformation via the description of mixed kinematic /isotropic linear plastic hardening based on the Mori-Tanaka homogenization. The theory of small strains is applied. Small strain fields, corresponding to phase transformation, are decomposed into the volumic and the shea...

  2. The surface-forming energy release rate based fracture criterion for elastic-plastic crack propagation

    Science.gov (United States)

    Xiao, Si; Wang, He-Ling; Liu, Bin; Hwang, Keh-Chih

    2015-11-01

    The J-integral based criterion is widely used in elastic-plastic fracture mechanics. However, it is not rigorously applicable when plastic unloading appears during crack propagation. One difficulty is that the energy density with plastic unloading in the J-integral cannot be defined unambiguously. In this paper, we alternatively start from the analysis on the power balance, and propose a surface-forming energy release rate (ERR), which represents the energy available for separating the crack surfaces during the crack propagation and excludes the loading-mode-dependent plastic dissipation. Therefore the surface-forming ERR based fracture criterion has wider applicability, including elastic-plastic crack propagation problems. Several formulae are derived for calculating the surface-forming ERR. From the most concise formula, it is interesting to note that the surface-forming ERR can be computed using only the stress and deformation of the current moment, and the definition of the energy density or work density is avoided. When an infinitesimal contour is chosen, the expression can be further simplified. For any fracture behaviors, the surface-forming ERR is proven to be path-independent, and the path-independence of its constituent term, so-called Js-integral, is also investigated. The physical meanings and applicability of the proposed surface-forming ERR, traditional ERR, Js-integral and J-integral are compared and discussed. Besides, we give an interpretation of Rice paradox by comparing the cohesive fracture model and the surface-forming ERR based fracture criterion.

  3. Statistical Tensile Strength for High Strain Rate of Aramid and UHMWPE Fibers

    Institute of Scientific and Technical Information of China (English)

    YANG Bin; XIONG Tao; XIONG Jie

    2006-01-01

    Dynamic tensile impact properties of aramid (Technora(R)) and UHMWPE (DC851) fiber bundles were studied at two high strain rates by means of reflecting type Split Hopkinson Bar, and stress-strain curves of fiber yarns at different strain rates were obtained. Experimental results show that the initial elastic modulus, failure strength and unstable strain of aramid fiber yarns are strain rate insensitive, whereas the initial elastic modulus and unstable strain of UHMWPE fiber yarns are strain rate sensitive. A fiber-bundle statistical constitutive equation was used to describe the tensile behavior of aramid and UHMWPE fiber bundles at high strain rates. The good consistency between the simulated results and experimental data indicates that the modified double Weibull function can represent the tensile strength distribution of aramid and UHMWPE fibers and the method of extracting Weibull parameters from fiber bundles stress-strain data is valid.

  4. Atomistic modeling at experimental strain rates and timescales

    Science.gov (United States)

    Yan, Xin; Cao, Penghui; Tao, Weiwei; Sharma, Pradeep; Park, Harold S.

    2016-12-01

    Modeling physical phenomena with atomistic fidelity and at laboratory timescales is one of the holy grails of computational materials science. Conventional molecular dynamics (MD) simulations enable the elucidation of an astonishing array of phenomena inherent in the mechanical and chemical behavior of materials. However, conventional MD, with our current computational modalities, is incapable of resolving timescales longer than microseconds (at best). In this short review article, we briefly review a recently proposed approach—the so-called autonomous basin climbing (ABC) method—that in certain instances can provide valuable information on slow timescale processes. We provide a general summary of the principles underlying the ABC approach, with emphasis on recent methodological developments enabling the study of mechanically-driven processes at slow (experimental) strain rates and timescales. Specifically, we show that by combining a strong physical understanding of the underlying phenomena, kinetic Monte Carlo, transition state theory and minimum energy pathway methods, the ABC method has been found to be useful in a variety of mechanically-driven problems ranging from the prediction of creep-behavior in metals, constitutive laws for grain boundary sliding, void nucleation rates, diffusion in amorphous materials to protein unfolding. Aside from reviewing the basic ideas underlying this approach, we emphasize some of the key challenges encountered in our own personal research work and suggest future research avenues for exploration.

  5. Anomalous enhancement of drilling rate in carbon fiber reinforced plastic using azimuthally polarized CO2 laser

    Science.gov (United States)

    Endo, Masamori; Araya, Naohiro; Kurokawa, Yuki; Uno, Kazuyuki

    2016-09-01

    We developed an azimuthally polarized pulse-periodic CO2 laser for high-performance drilling applications. We discovered an anomalous enhancement in the drilling rate with the azimuthally polarized beam compared to that with radially or randomly polarized beams. We drilled 0.45 mm-thick carbon fiber reinforced plastic (CFRP) using a focusing lens with a focal length of 50 mm and a numerical aperture (NA) of 0.09. The conditions other than polarization states were identical for all the experiments. The azimuthally polarized beam exhibited a drilling rate more than 10 times greater on average than those of the other two polarizations.

  6. Analysis of the tensile stress-strain behavior of elastomers at constant strain rates. I - Criteria for separability of the time and strain effects

    Science.gov (United States)

    Hong, S. D.; Fedors, R. F.; Schwarzl, F.; Moacanin, J.; Landel, R. F.

    1981-01-01

    A theoretical analysis of the tensile stress-strain relation of elastomers at constant strain rate is presented which shows that the time and the stress effect are separable if the experimental time scale coincides with a segment of the relaxation modulus that can be described by a single power law. It is also shown that time-strain separability is valid if the strain function is linearly proportional to the Cauchy strain, and that when time-strain separability holds, two strain-dependent quantities can be obtained experimentally. In the case where time and strain effect are not separable, superposition can be achieved only by using temperature and strain-dependent shift factors.

  7. Cellular basis of morphological variation and temperature-related plasticity in Drosophila melanogaster strains with divergent wing shapes.

    Science.gov (United States)

    Torquato, Libéria Souza; Mattos, Daniel; Matta, Bruna Palma; Bitner-Mathé, Blanche Christine

    2014-12-01

    Organ shape evolves through cross-generational changes in developmental patterns at cellular and/or tissue levels that ultimately alter tissue dimensions and final adult proportions. Here, we investigated the cellular basis of an artificially selected divergence in the outline shape of Drosophila melanogaster wings, by comparing flies with elongated or rounded wing shapes but with remarkably similar wing sizes. We also tested whether cellular plasticity in response to developmental temperature was altered by such selection. Results show that variation in cellular traits is associated with wing shape differences, and that cell number may play an important role in wing shape response to selection. Regarding the effects of developmental temperature, a size-related plastic response was observed, in that flies reared at 16 °C developed larger wings with larger and more numerous cells across all intervein regions relative to flies reared at 25 °C. Nevertheless, no conclusive indication of altered phenotypic plasticity was found between selection strains for any wing or cellular trait. We also described how cell area is distributed across different intervein regions. It follows that cell area tends to decrease along the anterior wing compartment and increase along the posterior one. Remarkably, such pattern was observed not only in the selected strains but also in the natural baseline population, suggesting that it might be canalized during development and was not altered by the intense program of artificial selection for divergent wing shapes.

  8. Assessment of strain and strain rate in embryonic chick heart in vivo using tissue Doppler optical coherence tomography

    Science.gov (United States)

    Li, Peng; Liu, Aiping; Shi, Liang; Yin, Xin; Rugonyi, Sandra; Wang, Ruikang K.

    2011-11-01

    We present a method to assess the in vivo radial strain and strain rate of the myocardial wall, which is of great importance to understand the biomechanics of cardiac development, using tissue Doppler optical coherence tomography (tissue-DOCT). Combining the structure and velocity information acquired from tissue-DOCT, the velocity distribution in the myocardial wall is plotted, from which the radial strain and strain rate are evaluated. The results demonstrate that tissue-DOCT can be used as a useful tool to describe tissue deformation, especially, the biomechanical characteristics of the embryonic heart.

  9. A Rate-Dependent Crystal Plasticity Analysis of Orientation Stability in Biaxial Tension of Magnesium

    Institute of Scientific and Technical Information of China (English)

    Donghong Zhang; Saiyi Li

    2011-01-01

    The development of texture during plastic deformation plays an important role in determining the stretch formability of magnesium alloy sheets. In this study, the orientation stability during equibiaxial tension of magnesium was analyzed based on three dimensional lattice rotations calculated by using a rate-dependent crystal plasticity model and assuming five different combinations of slip modes. The results show that no orientations can satisfy the stability criteria with both zero rotation velocity and convergent orientation flow in all dimensions. However, relatively stable orientations with zero rotation velocity and an overall convergence are found. They are featured by characteristic alignments of specific crystallographic directions in the macroscopic axis of contraction, depending on the slip modes involved in the deformation. It is also shown that the orientation stability varies significantly with the deviation of deformation mode from equibiaxial tension. The simulation results are briefly discussed in comparison with pre-existing experiments.

  10. High creep strain rates observed in nanocrystalline α-Fe{sub 2}O{sub 3} particles by nanoindentation measurement

    Energy Technology Data Exchange (ETDEWEB)

    Hajra, P.; Saha, D.R. [MLS Professor' s Unit, Indian Association for the Cultivation of Science, 2A and 2B Raja S.C. Mullick Road, Kolkata 700032 (India); Mada, M.R. [School of Materials Science and Engineering, Kensington, University of New South Wales, Sydney 2052 (Australia); Dutta, S. [Department of Physics, Rammohan College, 102/1 Raja Rammohan Roy Sarani, Kolkata 700009 (India); Brahma, P. [Department of Physics, Gurudas College, Kolkata 700054 (India); Boughton, P.; Bandyopadhyay, S. [School of Materials Science and Engineering, Kensington, University of New South Wales, Sydney 2052 (Australia); Chakravorty, D., E-mail: mlsdc@iacs.res.in [MLS Professor' s Unit, Indian Association for the Cultivation of Science, 2A and 2B Raja S.C. Mullick Road, Kolkata 700032 (India)

    2014-05-01

    Nanocrystalline α-Fe{sub 2}O{sub 3} with particle sizes in the range 10–24 nm were produced by mechanical milling of micron-sized α-Fe{sub 2}O{sub 3} particles. Microstructures of sintered pellets of cold compacted powder were investigated by electron microscopy. Nanoindentation studies showed the creep strain rates had values of the order of 10{sup −4} s{sup −1} at room temperature with creep increasing to higher values with increase of particle diameter. This was attributed to grain boundary sliding enhancement due to a piezomagnetic-type effect in the particles. Compressive tests at room temperature carried out on bulk samples with nanosized crystallites also showed large creep strain rate behaviour. The result will be helpful in designing ceramic systems with plastic behaviour at room temperature.

  11. Microstructure and annealing behavior of a modified 9Cr-1Mo steel after dynamic plastic deformation to different strains

    Science.gov (United States)

    Zhang, Z. B.; Mishin, O. V.; Tao, N. R.; Pantleon, W.

    2015-03-01

    The microstructure, hardness and tensile properties of a modified 9Cr-1Mo steel processed by dynamic plastic deformation (DPD) to different strains (0.5 and 2.3) have been investigated in the as-deformed and annealed conditions. It is found that significant structural refinement and a high level of strength can be achieved by DPD to a strain of 2.3, and that the microstructure at this strain contains a large fraction of high angle boundaries. The ductility of the DPD processed steel is however low. Considerable structural coarsening of the deformed microstructure without pronounced recrystallization takes place during annealing of the low-strain and high-strain samples for 1 h at 650 °C and 600 °C, respectively. Both coarsening and partial recrystallization occur in the high-strain sample during annealing at 650 °C for 1 h. For this sample, it is found that whereas coarsening alone results in a loss of strength with only a small gain in ductility, coarsening combined with pronounced partial recrystallization enables a combination of appreciably increased ductility and comparatively high strength.

  12. Microstructure and annealing behavior of a modified 9Cr−1Mo steel after dynamic plastic deformation to different strains

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Z.B.; Mishin, O.V. [Danish-Chinese Center for Nanometals, Section for Materials Science and Advanced Characterization, Department of Wind Energy, Technical University of Denmark, Risø Campus, 4000 Roskilde (Denmark); Sino-Danish Center for Education and Research (China); Sino-Danish Center for Education and Research (Denmark); Tao, N.R. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Science, Shenyang 110016 (China); Sino-Danish Center for Education and Research (China); Sino-Danish Center for Education and Research (Denmark); Pantleon, W., E-mail: pawo@dtu.dk [Section for Materials and Surface Engineering, Department of Mechanical Engineering, Technical University of Denmark, 2800 Kgs. Lyngby (Denmark); Sino-Danish Center for Education and Research (China); Sino-Danish Center for Education and Research (Denmark)

    2015-03-15

    The microstructure, hardness and tensile properties of a modified 9Cr−1Mo steel processed by dynamic plastic deformation (DPD) to different strains (0.5 and 2.3) have been investigated in the as-deformed and annealed conditions. It is found that significant structural refinement and a high level of strength can be achieved by DPD to a strain of 2.3, and that the microstructure at this strain contains a large fraction of high angle boundaries. The ductility of the DPD processed steel is however low. Considerable structural coarsening of the deformed microstructure without pronounced recrystallization takes place during annealing of the low-strain and high-strain samples for 1 h at 650 °C and 600 °C, respectively. Both coarsening and partial recrystallization occur in the high-strain sample during annealing at 650 °C for 1 h. For this sample, it is found that whereas coarsening alone results in a loss of strength with only a small gain in ductility, coarsening combined with pronounced partial recrystallization enables a combination of appreciably increased ductility and comparatively high strength.

  13. Experimental study of the compression properties of Al/W/PTFE granular composites under elevated strain rates

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, X.F., E-mail: lynx@mail.njust.edu.cn [School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China); Zhang, J.; Qiao, L.; Shi, A.S.; Zhang, Y.G.; He, Y. [School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China); Guan, Z.W. [School of Engineering, University of Liverpool, Brownlow Street, Liverpool L69 3GQ (United Kingdom)

    2013-10-01

    Granular composites consisting of aluminium (Al), tungsten (W) and polytetraflouroethylene (PTFE) are typical energetic materials, which possess high density and strength along with other advantageous properties. To investigate the mechanical behaviour of Al/W/PTFE granular composites, compression tests of three Al/W/PTFE mixtures under quasi-static loading and high strain rate conditions were conducted on a CSS-44100 Materials Testing System and a Split-Hopkinson Pressure Bar (SHPB), respectively. By employing Al bars, the amplitude of the transmitted signal was significantly enhanced and a high signal-to-noise ratio was obtained. This enhancement was due to the decreased Young's modulus of the bars, which led to increased signal amplitude from the strain gauges. The Al/W/PTFE granular composites were processed using a cold isostatic pressing and vacuum sintering approach. In this work, the fracture modes and stress-strain relationships of Al/W/PTFE composites with mass ratios of Al:W:PTFE of 24:0:76, 12:50:38 and 5.5:77:17.5 were studied. A detailed discussion is provided to cover the effect that tungsten addition, strain rate and mass ratio have on the deformation behaviour of the composites. The results show that the mass ratio plays a significant role in determining the dynamic behaviour and failure modes of the composites. Both the Al/W/PTFE (24:0:76) and the Al/W/PTFE (12:50:38) composites are strain rate dependent, elasto-plastic materials characterised by increased yield stress with increased strain rate. However, the Al/W/PTFE (5.5:77:17.5) composite is a brittle material, which shows brittle fracture at a relatively low strain.

  14. Dynamic neural networking as a basis for plasticity in the control of heart rate.

    Science.gov (United States)

    Kember, G; Armour, J A; Zamir, M

    2013-01-21

    A model is proposed in which the relationship between individual neurons within a neural network is dynamically changing to the effect of providing a measure of "plasticity" in the control of heart rate. The neural network on which the model is based consists of three populations of neurons residing in the central nervous system, the intrathoracic extracardiac nervous system, and the intrinsic cardiac nervous system. This hierarchy of neural centers is used to challenge the classical view that the control of heart rate, a key clinical index, resides entirely in central neuronal command (spinal cord, medulla oblongata, and higher centers). Our results indicate that dynamic networking allows for the possibility of an interplay among the three populations of neurons to the effect of altering the order of control of heart rate among them. This interplay among the three levels of control allows for different neural pathways for the control of heart rate to emerge under different blood flow demands or disease conditions and, as such, it has significant clinical implications because current understanding and treatment of heart rate anomalies are based largely on a single level of control and on neurons acting in unison as a single entity rather than individually within a (plastically) interconnected network. Copyright © 2012 Elsevier Ltd. All rights reserved.

  15. Annealing and strain rate effects on the mechanical behavior of ultrafine-grained iron produced by SPD

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    Thermal stability and strain rate sensitivity of ultrafine-grained(UFG)Fe produced by severe plastic deformation(SPD)were investigated.The UFG Fe was processed by equal-channel angular pressing(ECAP)via route Bc.After 6 passes,the grain size of UFG Fe reaches 600 nm, as confirmed by means of electron back scatter diffraction(EBSD).Examination of micro-hardness and grain size of UFG Fe as a function of post-ECAP annealing temperature shows a transition from recovery to recrystallization.The critical trans...

  16. Servohydraulic methods for mechanical testing in the Sub-Hopkinson rate regime up to strain rates of 500 1/s.

    Energy Technology Data Exchange (ETDEWEB)

    Crenshaw, Thomas B.; Boyce, Brad Lee

    2005-10-01

    Tensile and compressive stress-strain experiments on metals at strain rates in the range of 1-1000 1/s are relevant to many applications such as gravity-dropped munitions and airplane accidents. While conventional test methods cover strain rates up to {approx}10 s{sup -1} and split-Hopkinson and other techniques cover strain rates in excess of {approx}1000 s{sup -1}, there are no well defined techniques for the intermediate or ''Sub-Hopkinson'' strain-rate regime. The current work outlines many of the challenges in testing in the Sub-Hopkinson regime, and establishes methods for addressing these challenges. The resulting technique for obtaining intermediate rate stress-strain data is demonstrated in tension on a high-strength, high-toughness steel alloy (Hytuf) that could be a candidate alloy for earth penetrating munitions and in compression on a Au-Cu braze alloy.

  17. FEM solutions for plane stress mode-I and mode-II cracks in strain gradient plasticity

    Institute of Scientific and Technical Information of China (English)

    邱信明; 郭田福; 黄克智

    2000-01-01

    The strain gradient plasticity theory is used to investigate the crack-tip field in a power law hardening material. Numerical solutions are presented for plane-stress mode I and mode II cracks under small scale yielding conditions. A comparison is made with the existing asymptotic fields. It is found that the size of the dominance zone for the near-tip asymptotic field, recently obtained by Chen et al., is on the order 5% of the intrinsic material length I. Remote from the dominance zone, the computed stress field tends to be the classical HRR field. Within the plastic zone only force-stress dominated solution is found for either mode I or mode II crack.

  18. Inverse strain rate effect on cyclic stress response in annealed Zircaloy-2

    Energy Technology Data Exchange (ETDEWEB)

    Sudhakar Rao, G.; Verma, Preeti [Center of Advanced Study, Department of Metallurgical Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005 (India); Chakravartty, J.K. [Mechanical Metallurgy Group, Bhabha Atomic Research Center, Trombay 400 085, Mumbai (India); Nudurupati, Saibaba [Nuclear Fuel Complex, Hyderabad 500 062 (India); Mahobia, G.S.; Santhi Srinivas, N.C. [Center of Advanced Study, Department of Metallurgical Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005 (India); Singh, Vakil, E-mail: vsingh.met@itbhu.ac.in [Center of Advanced Study, Department of Metallurgical Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005 (India)

    2015-02-15

    Low cycle fatigue behavior of annealed Zircaloy-2 was investigated at 300 and 400 °C at different strain amplitudes and strain rates of 10{sup −2}, 10{sup −3}, and 10{sup −4} s{sup −1}. Cyclic stress response showed initial hardening with decreasing rate of hardening, followed by linear cyclic hardening and finally secondary hardening with increasing rate of hardening for low strain amplitudes at both the temperatures. The rate as well the degree of linear hardening and secondary hardening decreased with decrease in strain rate at 300 °C, however, there was inverse effect of strain rate on cyclic stress response at 400 °C and cyclic stress was increased with decrease in strain rate. The fatigue life decreased with decrease in strain rate at both the temperatures. The occurrence of linear cyclic hardening, inverse effect of strain rate on cyclic stress response and deterioration in fatigue life with decrease in strain rate may be attributed to dynamic strain aging phenomena resulting from enhanced interaction of dislocations with solutes. Fracture surfaces revealed distinct striations, secondary cracking, and oxidation with decrease in strain rate. Deformation substructure showed parallel dislocation lines and dislocation band structure at 300 °C. Persistent slip band wall structure and development of fine Corduroy structure was observed at 400 °C.

  19. Flow Curve Determination at Large Plastic Strain Levels to Accurately Constitutive Equations of AHSS in Forming Simulation

    Science.gov (United States)

    Lemoine, X.; Sriram, S.; Kergen, R.

    2011-05-01

    ArcelorMittal continuously develops new steel grades (AHSS) with high performance for the automotive industry to improve the weight reduction and the passive safety. The wide market introduction of AHSS raises a new challenge for manufacturers in terms of material models in the prediction of forming—especially formability and springback. The relatively low uniform elongation, the high UTS and the low forming limit curve of these AHSS may cause difficulties in forming simulations. One of these difficulties is the consequence of the relatively low uniform elongation on the parameters identification of isotropic hardening model. Different experimental tests allow to reach large plastic strain levels (hydraulic bulge test, stack compression test, shear test…). After a description on how to determine the flow curve in these experimental tests, a comparison of the different flow curves is made for different steel grades. The ArcelorMittal identification protocol for hardening models is only based on stress-strain curves determined in uniaxial tension. Experimental tests where large plastic strain levels are reached are used to validate our identification protocol and to recommend some hardening models. Finally, the influence of isotropic hardening models and yield loci in forming prediction for AHSS steels will be presented.

  20. Strain-rate sensitivity of foam materials: A numerical study using 3D image-based finite element model

    Science.gov (United States)

    Sun, Yongle; Li, Q. M.; Withers, P. J.

    2015-09-01

    Realistic simulations are increasingly demanded to clarify the dynamic behaviour of foam materials, because, on one hand, the significant variability (e.g. 20% scatter band) of foam properties and the lack of reliable dynamic test methods for foams bring particular difficulty to accurately evaluate the strain-rate sensitivity in experiments; while on the other hand numerical models based on idealised cell structures (e.g. Kelvin and Voronoi) may not be sufficiently representative to capture the actual structural effect. To overcome these limitations, the strain-rate sensitivity of the compressive and tensile properties of closed-cell aluminium Alporas foam is investigated in this study by means of meso-scale realistic finite element (FE) simulations. The FE modelling method based on X-ray computed tomography (CT) image is introduced first, as well as its applications to foam materials. Then the compression and tension of Alporas foam at a wide variety of applied nominal strain-rates are simulated using FE model constructed from the actual cell geometry obtained from the CT image. The stain-rate sensitivity of compressive strength (collapse stress) and tensile strength (0.2% offset yield point) are evaluated when considering different cell-wall material properties. The numerical results show that the rate dependence of cell-wall material is the main cause of the strain-rate hardening of the compressive and tensile strengths at low and intermediate strain-rates. When the strain-rate is sufficiently high, shock compression is initiated, which significantly enhances the stress at the loading end and has complicated effect on the stress at the supporting end. The plastic tensile wave effect is evident at high strain-rates, but shock tension cannot develop in Alporas foam due to the softening associated with single fracture process zone occurring in tensile response. In all cases the micro inertia of individual cell walls subjected to localised deformation is found to

  1. Effects of acceleration rate on Rayleigh-Taylor instability in elastic-plastic materials

    Science.gov (United States)

    Banerjee, Arindam; Polavarapu, Rinosh

    2016-11-01

    The effect of acceleration rate in the elastic-plastic transition stage of Rayleigh-Taylor instability in an accelerated non-Newtonian material is investigated experimentally using a rotating wheel experiment. A non-Newtonian material (mayonnaise) was accelerated at different rates by varying the angular acceleration of a rotating wheel and growth patterns of single mode perturbations with different combinations of amplitude and wavelength were analyzed. Experiments were run at two different acceleration rates to compare with experiments presented in prior years at APS DFD meetings and the peak amplitude responses are captured using a high-speed camera. Similar to the instability acceleration, the elastic-plastic transition acceleration is found to be increasing with increase in acceleration rate for a given amplitude and wavelength. The experimental results will be compared to various analytical strength models and prior experimental studies using Newtonian fluids. Authors acknowledge funding support from Los Alamos National Lab subcontract(370333) and DOE-SSAA Grant (DE-NA0001975).

  2. Strain-rate dependence for Ni/Al hybrid foams

    Directory of Open Access Journals (Sweden)

    Jung Anne

    2015-01-01

    Full Text Available Shock absorption often needs stiff but lightweight materials that exhibit a large kinetic energy absorption capability. Open-cell metal foams are artificial structures, which due to their plateau stress, including a strong hysteresis, can in principle absorb large amounts of energy. However, their plateau stress is too low for many applications. In this study, we use highly novel and promising Ni/Al hybrid foams which consist of standard, open-cell aluminium foams, where nanocrystalline nickel is deposited by electrodeposition as coating on the strut surface. The mechanical behaviour of cellular materials, including their behaviour under higher strain-rates, is governed by their microstructure due to the properties of the strut material, pore/strut geometry and mass distribution over the struts. Micro-inertia effects are strongly related to the microstructure. For a conclusive model, the exact real microstructure is needed. In this study a micro-focus computer tomography (μCT system has been used for the analysis of the microstructure of the foam samples and for the development of a microstructural Finite Element (micro-FE mesh. The microstructural FE models have been used to model the mechanical behaviour of the Ni/Al hybrid foams under dynamic loading conditions. The simulations are validated by quasi-static compression tests and dynamic split Hopkinson pressure bar tests.

  3. High pressure, high strain rate material strength studies

    Science.gov (United States)

    Remington, B. A.; Arsenlis, A.; Barton, N.; Belof, J.; Cavallo, R.; Maddox, B.; Park, H.-S.; Prisbrey, S.; Rudd, R.; Comley, A.; Meyers, M.; Wark, J.

    2011-10-01

    Constitutive models for material strength are currently being tested at high pressures by comparing 2D simulations with experiments measuring the Rayleigh-Taylor (RT) instability evolution in solid-state samples of vanadium (V), tantalum (Ta), and iron (Fe). The multiscale strength models being tested combine molecular dynamics, dislocation dynamics, and continuum simulations. Our analysis for the V experiments suggests that the material deformation at these conditions falls into the phonon drag regime, whereas for Ta, the deformation resides mainly in the thermal activation regime. Recent Fe-RT experiments suggest perturbation growth about the alpha-epsilon (bcc-hcp) phase transition threshold has been observed. Using the LLNL multiscale models, we decompose the strength as a function of strain rate into its dominant components of thermal activation, phonon drag, and work hardening. We have also developed a dynamic diffraction diagnostic technique to measure strength directly from shock compressed single crystal samples. Finally, recovery experiments allow a comparison of residual dislocation density with predictions from the multiscale model. This work performed under the auspices of the U.S. DoE by LLNL Security, LLC under Contract DE-AC52-07NA27344.

  4. Micro-scale measurements of plastic strain field, and local contributions of slip and twinning in TWIP steels during in situ tensile tests

    Energy Technology Data Exchange (ETDEWEB)

    Yang, H.K. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Laboratoire de Mécanique des Solides, Ecole Polytechnique, CNRS UMR7649, Université Paris-Saclay, 91128 Palaiseau (France); Doquet, V., E-mail: doquet@lms.polytechnique.fr [Laboratoire de Mécanique des Solides, Ecole Polytechnique, CNRS UMR7649, Université Paris-Saclay, 91128 Palaiseau (France); Zhang, Z.F. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China)

    2016-08-30

    In-situ tensile tests were carried out on Fe22Mn0.6C and Fe22Mn0.6C3Al (wt%) twinning-induced plasticity (TWIP) steels specimens covered with gold micro-grids. High resolution atomic force microscopy (AFM) and scanning electron microscope (SEM) images were periodically captured. The latter were used for measurements of the plastic strain field, using digital image correlation (DIC). Although no meso-scale localization bands appeared, some areas were deformed three times more than average. Plastic deformation inside the grains was more heterogeneous in Fe22Mn0.6C, but at meso-scale, the degree of strain heterogeneity was not higher, at least up to 12% strain. Plastic deformation started from grain boundaries or annealing twin boundaries in both materials, due to a high elastic anisotropy of the grains. An original method based on DIC was developed to estimate the twin fraction in grains that exhibit a single set of slip/twin bands. Deformation twinning accommodated 60–80% of the plastic strain in some favorably oriented grains, from the onset of plastic flow in Fe22Mn0.6C, but was not observed in the Al-bearing steel until 12% strain. The back stress was important in both materials, but significantly higher in Fe22Mn0.6C.

  5. A neuromorphic VLSI design for spike timing and rate based synaptic plasticity.

    Science.gov (United States)

    Rahimi Azghadi, Mostafa; Al-Sarawi, Said; Abbott, Derek; Iannella, Nicolangelo

    2013-09-01

    Triplet-based Spike Timing Dependent Plasticity (TSTDP) is a powerful synaptic plasticity rule that acts beyond conventional pair-based STDP (PSTDP). Here, the TSTDP is capable of reproducing the outcomes from a variety of biological experiments, while the PSTDP rule fails to reproduce them. Additionally, it has been shown that the behaviour inherent to the spike rate-based Bienenstock-Cooper-Munro (BCM) synaptic plasticity rule can also emerge from the TSTDP rule. This paper proposes an analogue implementation of the TSTDP rule. The proposed VLSI circuit has been designed using the AMS 0.35 μm CMOS process and has been simulated using design kits for Synopsys and Cadence tools. Simulation results demonstrate how well the proposed circuit can alter synaptic weights according to the timing difference amongst a set of different patterns of spikes. Furthermore, the circuit is shown to give rise to a BCM-like learning rule, which is a rate-based rule. To mimic an implementation environment, a 1000 run Monte Carlo (MC) analysis was conducted on the proposed circuit. The presented MC simulation analysis and the simulation result from fine-tuned circuits show that it is possible to mitigate the effect of process variations in the proof of concept circuit; however, a practical variation aware design technique is required to promise a high circuit performance in a large scale neural network. We believe that the proposed design can play a significant role in future VLSI implementations of both spike timing and rate based neuromorphic learning systems.

  6. Microtwin formation in the {alpha} phase of duplex titanium alloys affected by strain rate

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Yi-Hsiang; Wu, Shu-Ming [Department of Mechanical and Mechatronic Engineering, National Taiwan Ocean University, No. 2 Pei Ning Road, Keelung 20224, Taiwan (China); Kao, Fang-Hsin [Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan (China); Wang, Shing-Hoa, E-mail: shwang@ntou.edu.tw [Department of Mechanical and Mechatronic Engineering, National Taiwan Ocean University, No. 2 Pei Ning Road, Keelung 20224, Taiwan (China); Yang, Jer-Ren [Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan (China); Yang, Chia-Chih [Department of Mechanical and Mechatronic Engineering, National Taiwan Ocean University, No. 2 Pei Ning Road, Keelung 20224, Taiwan (China); Chiou, Chuan-Sheng [Department of Mechanical Engineering, Yuan Ze University, Taoyuan 32003, Taiwan (China)

    2011-03-15

    Research highlights: {yields} The long and dense twins in {alpha} phase of SP700 alloy occurring at lower strain rates promote a good ductility. {yields} The deformation in SP700 alloy changed to micro twins-controlled mechanism in {alpha} as the strain rate decreases. {yields} The material has time to redistribute the deformed strain between {alpha} and {beta} as the strain rate decreases. - Abstract: The effect of tensile strain rate on deformation microstructure was investigated in Ti-6-4 (Ti-6Al-4V) and SP700 (Ti-4.5Al-3V-2Mo-2Fe) of the duplex titanium alloys. Below a strain rate of 10{sup -2} s{sup -1}, Ti-6-4 alloy had a higher ultimate tensile strength than SP700 alloy. However, the yield strength of SP700 was consistently greater than Ti-6-4 at different strain rates. The ductility of SP700 alloy associated with twin formation (especially at the slow strain rate of 10{sup -4} s{sup -1}), always exceeded that of Ti-6-4 alloy at different strain rates. It is caused by a large quantity of deformation twins took place in the {alpha} phase of SP700 due to the lower stacking fault energy by the {beta} stabilizer of molybdenum alloying. In addition, the local deformation more was imposed on the {alpha} grains from the surrounding {beta}-rich grains by redistributing strain as the strain rate decreased in SP700 duplex alloy.

  7. A general methodology for full-field plastic strain measurements using X-ray absorption tomography and internal markers

    DEFF Research Database (Denmark)

    Haldrup, Martin Kristoffer; Nielsen, Søren Fæster; Wert, John A.

    2008-01-01

    Probing the strain locally and throughout the bulk of various materials has long been of interest in Materials Science. This article presents a general methodology for assessing the plastic strain in terms of the displacement gradient tensor throughout the bulk of opaque samples. The method relies...... on a homogenous distribution of marker particles throughout the bulk of a sample, markers which are detected through the application of synchrotron X-ray tomography. Making use of the morphology of individual markers, motion of individual markers is tracked during deformation allowing the local displacement field...... to be determined throughout the bulk. The local displacement gradient tensor is derived from the displacement field. Spatial resolution is directly related to marker particle density in the sample, here 30 mu m. The accuracy of the displacement gradient tensor calculation is dependent on the accuracy with which...

  8. Effect of slow plastic and elastic straining on sulphide stress cracking and hydrogen embrittlement of 3. 5% Ni steel and APL 5L X60 pipeline steel

    Energy Technology Data Exchange (ETDEWEB)

    Erlings, J.G.; Groot, H.W. de; Nauta, J.

    1987-01-01

    A procedure is presented with which the roles of elastic and elastic-plastic straining in stress corrosion cracking (SCC) and hydrogen embrittlement (HE) can be determined. Premature failure of 3.5% Ni steels in sour and sweet environments due to SCC was only found when slow plastic straining was applied. With purely elastic slow straining the material remained crack-free, even in a buffered NACE solution. Depending on the sourness of the environment, the API 5L X60 pipeline material did not always need plastic straining to suffer HE cracking. Under none of the test conditions studied was hardened material susceptible to SCC or HE cracking. The non-hardened material tested was not susceptible to SCC in the various CO/sub 2/- and/or H/sub 2/S-containing media used.

  9. Experimentation and Modeling of the Tension Behavior of Polycarbonate at High Strain Rates

    Directory of Open Access Journals (Sweden)

    Yingjie Xu

    2016-02-01

    Full Text Available A comprehensive understanding of the mechanical behavior of polycarbonate (PC under high-rate loadings is essential for better design of PC products. In this work, the mechanical behavior of PC is studied during tensile loading at high strain rates, using a split Hopkinson tension bar (SHTB. A modified experimental technique based on the SHTB is proposed to perform the tension testing on PC at rates exceeding 1000 s−1. The effect of strain rates on the tension stress–strain law of PC is investigated over a wide range of strain rates (0.0005–4500 s−1. Based on the experiments, a physically based constitutive model is developed to describe the strain rate dependent tensile stress–strain law. The high rate tensile deformation mechanics of PC are further studied via finite element simulations using the LSDYNA code together with the developed constitutive model.

  10. Mechanical and microstructural characterization of a HMX-based pressed explosive: Effects of combined high pressure and strain rate

    Directory of Open Access Journals (Sweden)

    Biessy M.

    2012-08-01

    Full Text Available The paper presents a study of the combined effects of strain rate and confining pressure on the behaviour and microstructure evolutions of a HMX-based explosive. Hopkinson bar compression experiments are carried-out on samples confined with a brass sleeve. The latter is instrumented in order to determine the confining pressure on the explosive sample, directly function of the sleeve thickness and yield strength. A sample confined at 75 MPa and deformed at 250s−1 is recovered, cross-sectioned and studied using optical microscopy. Distributed microplasticity and microcracking appear similar to those induced by confined quasi-static experiments, indicating that stress triaxiality is the most important loading parameter. The sample also displays a large shear macrocrack, resulting from the formation of an adiabatic shear band. Shear banding seems to proceed by strong plastic strain gradients, followed by dynamic re-crystallization. Further strong thermal effects are observed, resulting in local reactive melting.

  11. Evaluation of thermal effects and strain-rate sensitivity in frozen soil

    Directory of Open Access Journals (Sweden)

    Zhu Zhi-Wu

    2014-01-01

    Full Text Available Temperature variation is one important factor that affects the dynamic mechanical properties of frozen soil under impact loading. Thermal damage is a collective phenomenon that can be caused by temperature variation. This paper investigates the effects of thermal damage on strain course. A split Hopkinson pressure bar was employed to investigate the dynamic mechanical characteristics of frozen soil at different temperatures and different strain rates. The stress-strain curves were obtained under impact loading. The compressive strength of frozen soil showed a negative temperature sensitivity and positive strain-rate trend. Specifically, the strength of frozen soil increased with decreasing temperatures and increasing strain rates.

  12. Determining the Mechanical Constitutive Properties of Metals as Function of Strain Rate and temperature: A Combined Experimental and Modeling Approach

    Energy Technology Data Exchange (ETDEWEB)

    Ian Robertson

    2007-04-28

    Development and validation of constitutive models for polycrystalline materials subjected to high strain-rate loading over a range of temperatures are needed to predict the response of engineering materials to in-service type conditions. To account accurately for the complex effects that can occur during extreme and variable loading conditions, requires significant and detailed computational and modeling efforts. These efforts must be integrated fully with precise and targeted experimental measurements that not only verify the predictions of the models, but also provide input about the fundamental processes responsible for the macroscopic response. Achieving this coupling between modeling and experiment is the guiding principle of this program. Specifically, this program seeks to bridge the length scale between discrete dislocation interactions with grain boundaries and continuum models for polycrystalline plasticity. Achieving this goal requires incorporating these complex dislocation-interface interactions into the well-defined behavior of single crystals. Despite the widespread study of metal plasticity, this aspect is not well understood for simple loading conditions, let alone extreme ones. Our experimental approach includes determining the high-strain rate response as a function of strain and temperature with post-mortem characterization of the microstructure, quasi-static testing of pre-deformed material, and direct observation of the dislocation behavior during reloading by using the in situ transmission electron microscope deformation technique. These experiments will provide the basis for development and validation of physically-based constitutive models. One aspect of the program involves the direct observation of specific mechanisms of micro-plasticity, as these indicate the boundary value problem that should be addressed. This focus on the pre-yield region in the quasi-static effort (the elasto-plastic transition) is also a tractable one from an

  13. High-rate deposition of nano-crystalline silicon thin films on plastics

    Energy Technology Data Exchange (ETDEWEB)

    Marins, E.; Guduru, V.; Cerqueira, F.; Alpuim, P. [Centro de Fisica, Universidade do Minho, 4800-058 Guimaraes, 4710-057 Braga (Portugal); Ribeiro, M. [Centro de Nanotecnologia e Materiais Tecnicos, Funcionais e Inteligentes (CeNTI), 4760-034 Vila Nova de Famalicao (Portugal); Bouattour, A. [Institut fuer Physikalische Elektronik (ipe), Universitaet Stuttgart, 70569 Stuttgart (Germany)

    2011-03-15

    Nanocrystalline silicon (nc-Si:H) is commonly used in the bottom cell of tandem solar cells. With an indirect bandgap, nc-Si:H requires thicker ({proportional_to}1 {mu}m) films for efficient light harvesting than amorphous Si (a-Si:H) does. Therefore, thin-film high deposition rates are crucial for further cost reduction of highly efficient a-Si:H based photovoltaic technology. Plastic substrates allow for further cost reduction by enabling roll-to-roll inline deposition. In this work, high nc-Si:H deposition rates on plastic were achieved at low substrate temperature (150 C) by standard Radio-frequency (13.56 MHz) Plasma Enhanced Chemical Vapor Deposition. Focus was on the influence of deposition pressure, inter-electrode distance (1.2 cm) and high power coupled to the plasma, on the hydrogen-to-silane dilution ratios (HD) necessary to achieve the amorphous-to-nanocrystalline phase transition and on the resulting film deposition rate. For each pressure and rf-power, there is a value of HD for which the films start to exhibit a certain amount of crystalline fraction. For constant rf-power, this value increases with pressure. Within the parameter range studied the deposition rate was highest (0.38 nm/s) for nc-Si:H films deposited at 6 Torr, 700 mW/cm{sup 2} using HD of 98.5%. Decreasing the pressure to 3 Torr (1.5 Torr) and rf-power to 350 mW/cm{sup 2} using HD - 98.5% deposition rate is 0.12 nm/s (0.076 nm/s). Raman crystalline fraction of these films is 72, 62 and 53% for the 6, 3 and 1.5 Torr films, respectively (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. Implementation of an Associative Flow Rule Including Hydrostatic Stress Effects Into the High Strain Rate Deformation Analysis of Polymer Matrix Composites

    Science.gov (United States)

    Goldberg, Robert K.; Roberts, Gary D.; Gilat, Amos

    2003-01-01

    A previously developed analytical formulation has been modified in order to more accurately account for the effects of hydrostatic stresses on the nonlinear, strain rate dependent deformation of polymer matrix composites. State variable constitutive equations originally developed for metals have been modified in order to model the nonlinear, strain rate dependent deformation of polymeric materials. To account for the effects of hydrostatic stresses, which are significant in polymers, the classical J2 plasticity theory definitions of effective stress and effective inelastic strain, along with the equations used to compute the components of the inelastic strain rate tensor, are appropriately modified. To verify the revised formulation, the shear and tensile deformation of two representative polymers are computed across a wide range of strain rates. Results computed using the developed constitutive equations correlate well with experimental data. The polymer constitutive equations are implemented within a strength of materials based micromechanics method to predict the nonlinear, strain rate dependent deformation of polymer matrix composites. The composite mechanics are verified by analyzing the deformation of a representative polymer matrix composite for several fiber orientation angles across a variety of strain rates. The computed values compare well to experimentally obtained results.

  15. Temperature effects on high strain rate properties of graphite/epoxy composites

    Science.gov (United States)

    Yaniv, G.; Daniel, I. M.; Cokeing, S.; Martinez, G. M.

    1991-01-01

    A unidirectional graphite epoxy material (AS4/3501-6) was characterized at strain rates ranging from 5 x 10(exp 6) s(exp -1) to 5(exp -1), at room temperature and at 128 C. Results are presented in the form of stress-strain curves to failure. The longitudinal properties remain nearly unchanged with strain rate and temperature. The transverse modulus increases with strain rate but decreases with temperature. The transverse strength and transverse ultimate tensile strain have a positive rate sensitivity at low rates, which changes to negative at intermediate rates and returns to positive rate sensitivity at the highest rates tested. A temperature-time equivalence principle was applied and master curves were obtained for the transverse mechanical properties. The in-plane shear modulus and in-plane shear strength have a positive rate sensitivity. The ultimate intralaminar shear strain has a positive rate sensitivity at low rates, which changes to negative at high rates. At the elevated temperature of 128 C, the ultimate shear strain is 25 to 30 percent higher than the room temperature value, but its strain rate dependence is moderate.

  16. Basic Strain Gradient Plasticity Theories with Application to Constrained Film Deformation

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Hutchinson, John W.

    2011-01-01

    with the deformation theory under proportional straining, analogous to the corresponding coincidence in the conventional J(2) theories. The generality of proportional straining is demonstrated for pure power-law materials, and the utility of power-law solutions is illustrated for the constrained deformation of thin...

  17. Instability criterion for the system composed of elastic beam and strain-softening pillar based on gradient-dependent plasticity

    Institute of Scientific and Technical Information of China (English)

    Xuebin Wang

    2005-01-01

    A mechanical model is proposed for the system of elastic beam and strain-softening pillar where strain localization is initiated at peak shear stress. To obtain the plastic deformation of the pillar due to the shear slips of multiple shear bands, the pillar is divided into several narrow slices where compressive deformation is treated as uniformity. In the light of the compatibility condition of deformation, the total compressive displacement of the pillar is equal to the displacement of the beam in the middle span. An insta bility criterion is derived analytically based on the energy principle using a known size of localization band according to gradientdependent plasticity. The main advantage of the present model is that the effects of the constitutive parameters of rock and the geometrical size of structure are reflected in the criterion. The condition that the derivative of distributed load with respect to the deflection of the beam in the middle span is less than zero is not only equivalent to, but also even more concise in form than the instability criterion. To study the influences of constitutive parameters and geometrical size on stability, some examples are presented.

  18. Microstructure of Cu60Zr20Ti20 bulk metallic glass rolled at different strain rates

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The structural evolution of Cu60Zr20Ti20 bulk metallic glass during rolling at different strain rates and cryogenic temperature was investigated by X-ray diffraction (XRD),differential scanning calorimetry (DSC) and high-resolution transmission electron microscopy (HRTEM). It is revealed that the deformation-induced transformation is strongly dependent on the strain rate. At the lowest experimental strain rate of 1.0×10-4 s-1,no phase transformation occurs until the highest deformation degree reaches 95%. In a strain rate range of 5.0×10-4-5.0×10-2 s-1,phase separation oc-curs in a high deformation degree. As the strain rate reaches 5.0×10-1 s-1,phase separation and nanocrystallization concur. The critical deformation degree for oc-currence of phase transformation decreases with the strain rate increasing.

  19. Strain rate and shear stress at the grain scale generated during near equilibrium antigorite dehydration

    Science.gov (United States)

    Padrón-Navarta, José Alberto; Tommasi, Andréa; Garrido, Carlos J.; Mainprice, David; Clément, Maxime

    2016-04-01

    Dehydration reactions are an outstanding case of mineral replacement reactions because they produce a significant transient fluid-filled porosity. Because fluids are present, these reactions occur by interface-coupled dissolution-precipitation. Under poorly drained conditions corresponding to foliated metamorphic rocks, they generate fluid pressure gradients that evolve in time and space eventually controlling fluid migration [1]. Despite the general agreement on this fact, we still lack of a precise knowledge of the complex coupling between the stresses generated during the reaction and the timescales for mineral growth and how they ultimate control the rate of fluid migration. Constraining these rates is challenge because the timescales of the feedback between fluid flow and mineral growth rates at near equilibrium are beyond the current experimental capabilities. For instance, numerical simulations suggest that the draining times of a dehydration front by compaction are in the order of 10-100 ky [1] difficult to translate into experimental strain rates. On the other hand, the natural record of dehydration reaction might potentially provide unique constrains on this feedback, but we need to identify microstructures related to compaction and quantify them. Features interpreted as due to compaction have been identified in a microstructural study [2] of the first stages of the antigorite dehydration at high-pressure conditions in Cerro del Almirez, Spain (ca. 1.6-1.9 GPa and 630-710 ° C). Compaction features can be mostly observed in the metamorphic enstatite in the form of (1) gradual crystallographic misorientation (up to 16°) of prismatic crystals due to buckling, (3) localized orthoenstatite(Pbca)/low clinoenstatite (P21/c) inversion (confirmed optically and by means of Electron Backscattered Diffraction) and (4) brittle fracturing of prismatic enstatite wrapped by plastically deformed chlorite. The coexistence of enstatite buckling and clinoenstatite lamellae

  20. Strain rate effect on sooting characteristics in laminar counterflow diffusion flames

    KAUST Repository

    Wang, Yu

    2016-01-20

    The effects of strain rate, oxygen enrichment and fuel type on the sooting characteristics of counterflow diffusion flames were studied. The sooting structures and relative PAH concentrations were measured with laser diagnostics. Detailed soot modeling using recently developed PAH chemistry and surface reaction mechanism was performed and the results were compared with experimental data for ethylene flames, focusing on the effects of strain rates. The results showed that increase in strain rate reduced soot volume fraction, average size and peak number density. Increase in oxygen mole fraction increased soot loading and decreased its sensitivity on strain rate. The soot volume fractions of ethane, propene and propane flames were also measured as a function of global strain rate. The sensitivity of soot volume fraction to strain rate was observed to be fuel dependent at a fixed oxygen mole fraction, with the sensitivity being higher for more sooting fuels. However, when the soot loadings were matched at a reference strain rate for different fuels by adjusting oxygen mole fraction, the dependence of soot loading on strain rate became comparable among the tested fuels. PAH concentrations were shown to decrease with increase in strain rate and the dependence on strain rate is more pronounced for larger PAHs. Soot modeling was performed using detailed PAH growth chemistry with molecular growth up to coronene. A qualitative agreement was obtained between experimental and simulation results, which was then used to explain the experimentally observed strain rate effect on soot growth. However, quantitatively, the simulation result exhibits higher sensitivity to strain rate, especially for large PAHs and soot volume fractions.

  1. Mechanical properties of biaxially strained poly(L-lactide) tubes: Strain rate and temperature dependence

    DEFF Research Database (Denmark)

    Løvdal, Alexandra Liv Vest; Andreasen, Jens Wenzel; Mikkelsen, Lars Pilgaard

    2017-01-01

    Poly(l-lactide) (PLLA) is a bioabsorbable polymer with high stiffness and strength compared to the other commercially available bioabsorbable polymers. The properties of PLLA can be improved by straining, causing deformation-mediated molecular orientation. PLLA tubes were biaxially strained above...

  2. Understanding the deformation of ceramic materials at high strain rates.

    OpenAIRE

    Hallam, David A.

    2015-01-01

    Ceramic hardness and plasticity have been highlighted as important characteristics in ballistic performance; both of which can be measured and semi-quantified from indentation experiments, respectively. However, relatively little work has investigated the accompanying type, on-set and evolution of indentation-induced damage that may also be contributing an influential role. Pressureless sintered SiC and spark plasma sintered B4C, SiC-AlN-C and range of SiC-B4C composite samples were invest...

  3. Insertion sequence content reflects genome plasticity in strains of the root nodule actinobacterium Frankia

    Directory of Open Access Journals (Sweden)

    Tisa Louis S

    2009-10-01

    Full Text Available Abstract Background Genome analysis of three Frankia sp. strains has revealed a high number of transposable elements in two of the strains. Twelve out of the 20 major families of bacterial Insertion Sequence (IS elements are represented in the 148 annotated transposases of Frankia strain HFPCcI3 (CcI3 comprising 3% of its total coding sequences (CDS. EAN1pec (EAN has 183 transposase ORFs from 13 IS families comprising 2.2% of its CDS. Strain ACN14a (ACN differs significantly from the other strains with only 33 transposase ORFs (0.5% of the total CDS from 9 IS families. Results Insertion sequences in the Frankia genomes were analyzed using BLAST searches, PHYML phylogenies and the IRF (Inverted Repeat Finder algorithms. To identify putative or decaying IS elements, a PSI-TBLASTN search was performed on all three genomes, identifying 36%, 39% and 12% additional putative transposase ORFs than originally annotated in strains CcI3, EAN and ACN, respectively. The distribution of transposase ORFs in each strain was then analysed using a sliding window, revealing significant clustering of elements in regions of the EAN and CcI3 genomes. Lastly the three genomes were aligned with the MAUVE multiple genome alignment tool, revealing several Large Chromosome Rearrangement (LCR events; many of which correlate to transposase clusters. Conclusion Analysis of transposase ORFs in Frankia sp. revealed low inter-strain diversity of transposases, suggesting that the majority of transposase proliferation occurred without recent horizontal transfer of novel mobile elements from outside the genus. Exceptions to this include representatives from the IS3 family in strain EAN and seven IS4 transposases in all three strains that have a lower G+C content, suggesting recent horizontal transfer. The clustering of transposase ORFs near LCRs revealed a tendency for IS elements to be associated with regions of chromosome instability in the three strains. The results of this

  4. Effect of Temperature and Strain Rate on Dynamic Properties of Low Silicon TRIP Steel

    Institute of Scientific and Technical Information of China (English)

    TIAN Rong; LI Lin; B C De Cooman; WEI Xi-chen; SUN Peng

    2006-01-01

    The dynamic tensile test of 0.11C-0.62Si-1.65Mn TRIP steel was carried out at different strain rates and test temperatures. The results show that both temperature and strain rate affect the retained austenite transformation. At high strain rates, the uniform elongation decreases, whereas the total elongation and energy absorption increase. The tensile strength is less strain rate sensitive. With raising test temperature, the tensile strength is reduced and the mechanical properties generally deteriorate, especially at 110 ℃. However, excellent mechanical properties were obtained at 50 ℃ and 75 ℃.

  5. Effect of microstructure on anomalous strain-rate-dependent behaviour of bacterial cellulose hydrogel.

    Science.gov (United States)

    Gao, Xing; Shi, Zhijun; Lau, Andrew; Liu, Changqin; Yang, Guang; Silberschmidt, Vadim V

    2016-05-01

    This study is focused on anomalous strain-rate-dependent behaviour of bacterial cellulose (BC) hydrogel that can be strain-rate insensitive, hardening, softening, or strain-rate insensitive in various ranges of strain rate. BC hydrogel consists of randomly distributed nanofibres and a large content of free water; thanks to its ideal biocompatibility, it is suitable for biomedical applications. Motivated by its potential applications in complex loading conditions of body environment, its time-dependent behaviour was studied by means of in-aqua uniaxial tension tests at constant temperature of 37 °C at various strain rates ranging from 0.000 1s(-1) to 0.3s(-1). Experimental results reflect anomalous strain-rate-dependent behaviour that was not documented before. Micro-morphological observations allowed identification of deformation mechanisms at low and high strain rates in relation to microstructural changes. Unlike strain-rate softening behaviours in other materials, reorientation of nanofibres and kinematics of free-water flow dominate the softening behaviour of BC hydrogel at high strain rates.

  6. Effect of strain rate on bake hardening response of BH220 steel

    Directory of Open Access Journals (Sweden)

    Das Anindya

    2015-01-01

    Full Text Available This study aims at understanding the bake hardening ability of ultra low carbon BH220 steel at different strain rates. The as-received material has been pre-strained to four different levels and then deformed in tension under (a as pre-strained state and (b after baking at 170 ∘C for 20 minutes, at three different strain rates of 0.001, 0.1 and 100/s. In both the conditions, yield stress increased with pre-strain and strain rate, but bake hardening ability was found to decrease when strain rate was increased. The strain rate sensitivity of the material was also found to decrease with bake hardening. Generation of dislocation forests and their subsequent immobility during baking treatment enables them to act as long range obstacles during further deformation. At higher strain rates, less amount of dislocations are produced which can interact with themselves and produce hardening, because of which bake hardening ability and the strain rate drops. A dislocation based strengthening model, as proposed by Larour et al. 2011 [7], was used to predict the yield stress values obtained at different conditions. The equation produced excellent co-relation with the experimental data.

  7. Method for obtaining simple shear material properties of the intervertebral disc under high strain rates.

    Science.gov (United States)

    Ott, Kyle A; Armiger, Robert S; Wickwire, Alexis C; Carneal, Catherine M; Trexler, Morgana M; Lennon, Andrew M; Zhang, Jiangyue; Merkle, Andrew C

    2012-01-01

    Predicting spinal injury under high rates of vertical loading is of interest, but the success of computational models in modeling this type of loading scenario is highly dependent on the material models employed. Understanding the response of these biological materials at high strain rates is critical to accurately model mechanical response of tissue and predict injury. While data exists at lower strain rates, there is a lack of the high strain rate material data that are needed to develop constitutive models. The Split Hopkinson Pressure Bar (SHPB) has been used for many years to obtain properties of various materials at high strain rates. However, this apparatus has mainly been used for characterizing metals and ceramics and is difficult to apply to softer materials such as biological tissue. Recently, studies have shown that modifications to the traditional SHPB setup allow for the successful characterization of mechanical properties of biological materials at strain rates and peak strain values that exceed alternate soft tissue testing techniques. In this paper, the previously-reported modified SHPB technique is applied to characterize human intervertebral disc material under simple shear. The strain rates achieved range from 5 to 250 strain s-1. The results demonstrate the sensitivity to the disc composition and structure, with the nucleus pulposus and annulus fibrosus exhibiting different behavior under shear loading. Shear tangent moduli are approximated at varying strain levels from 5 to 20% strain. This data and technique facilitates determination of mechanical properties of intervertebral disc materials under shear loading, for eventual use in constitutive models.

  8. Finite element analysis of the high strain rate testing of polymeric materials

    Science.gov (United States)

    Gorwade, C. V.; Alghamdi, A. S.; Ashcroft, I. A.; Silberschmidt, V. V.; Song, M.

    2012-08-01

    Advanced polymer materials are finding an increasing range of industrial and defence applications. Ultra-high molecular weight polymers (UHMWPE) are already used in lightweight body armour because of their good impact resistance with light weight. However, a broader use of such materials is limited by the complexity of the manufacturing processes and the lack of experimental data on their behaviour and failure evolution under high-strain rate loading conditions. The current study deals with an investigation of the internal heat generation during tensile of UHMWPE. A 3D finite element (FE) model of the tensile test is developed and validated the with experimental work. An elastic-plastic material model is used with adiabatic heat generation. The temperature and stresses obtained with FE analysis are found to be in a good agreement with the experimental results. The model can be used as a simple and cost effective tool to predict the thermo-mechanical behaviour of UHMWPE part under various loading conditions.

  9. Mechanical behaviour of glass fibre reinforced composite at varying strain rates

    Science.gov (United States)

    Acharya, Saikat; Mondal, D. K.; Ghosh, K. S.; Mukhopadhyay, A. K.

    2017-03-01

    Here we report the results of compressive split Hopkinson pressure bar experiments (SHPB) conducted on unidirectional glass fibre reinforced polymer (GFRP) in the strain rate regime 5  ×  102–1.3  ×  103 s‑1. The maximum compressive strength of GFRP was found to increase by as much as 55% with increase in strain rate. However, the corresponding relative strain to failure response was measured to increase only marginally with increase in strain rates. Based on the experimental results and photomicrographs obtained from FE-SEM based post mortem examinations, the failure phenomena are suggested to be associated with increase in absorption of energy from low to high strain rates. Attempts have been made to explain these observations in terms of changes in deformation mechanisms primarily as a function of strain rates.

  10. Constitutive modeling of strain rate effects in nanocrystalline and ultrafine grained polycrystals

    KAUST Repository

    Gurses, Ercan

    2011-05-01

    We present a variational two-phase constitutive model capable of capturing the enhanced rate sensitivity in nanocrystalline (nc) and ultrafine-grained (ufg) fcc metals. The nc/ufg-material consists of a grain interior phase and a grain boundary affected zone (GBAZ). The behavior of the GBAZ is described by a rate-dependent isotropic porous plasticity model, whereas a rate-independent crystal-plasticity model which accounts for the transition from partial dislocation to full dislocation mediated plasticity is employed for the grain interior. The scale bridging from a single grain to a polycrystal is done by a Taylor-type homogenization. It is shown that the enhanced rate sensitivity caused by the grain size refinement is successfully captured by the proposed model. © 2011 Elsevier Ltd. All rights reserved.

  11. Dynamic Mechanical Response of Biomedical 316L Stainless Steel as Function of Strain Rate and Temperature.

    Science.gov (United States)

    Lee, Woei-Shyan; Chen, Tao-Hsing; Lin, Chi-Feng; Luo, Wen-Zhen

    2011-01-01

    A split Hopkinson pressure bar is used to investigate the dynamic mechanical properties of biomedical 316L stainless steel under strain rates ranging from 1 × 10(3) s(-1) to 5 × 10(3) s(-1) and temperatures between 25°C and 800°C. The results indicate that the flow stress, work-hardening rate, strain rate sensitivity, and thermal activation energy are all significantly dependent on the strain, strain rate, and temperature. For a constant temperature, the flow stress, work-hardening rate, and strain rate sensitivity increase with increasing strain rate, while the thermal activation energy decreases. Catastrophic failure occurs only for the specimens deformed at a strain rate of 5 × 10(3) s(-1) and temperatures of 25°C or 200°C. Scanning electron microscopy observations show that the specimens fracture in a ductile shear mode. Optical microscopy analyses reveal that the number of slip bands within the grains increases with an increasing strain rate. Moreover, a dynamic recrystallisation of the deformed microstructure is observed in the specimens tested at the highest temperature of 800°C.

  12. Strain-based plastic instability acceptance criteria for ferritic steel safety class 1 nuclear components under level D service loads

    Directory of Open Access Journals (Sweden)

    Ji-Su Kim

    2015-04-01

    Full Text Available This paper proposes strain-based acceptance criteria for assessing plastic instability of the safety class 1 nuclear components made of ferritic steel during level D service loads. The strain-based criteria were proposed with two approaches: (1 a section average approach and (2 a critical location approach. Both approaches were based on the damage initiation point corresponding to the maximum load-carrying capability point instead of the fracture point via tensile tests and finite element analysis (FEA for the notched specimen under uni-axial tensile loading. The two proposed criteria were reviewed from the viewpoint of design practice and philosophy to select a more appropriate criterion. As a result of the review, it was found that the section average approach is more appropriate than the critical location approach from the viewpoint of design practice and philosophy. Finally, the criterion based on the section average approach was applied to a simplified reactor pressure vessel (RPV outlet nozzle subject to SSE loads. The application shows that the strain-based acceptance criteria can consider cumulative damages caused by the sequential loads unlike the stress-based acceptance criteria and can reduce the overconservatism of the stress-based acceptance criteria, which often occurs for level D service loads.

  13. On the formulations of higher-order strain gradient crystal plasticity models

    DEFF Research Database (Denmark)

    Kuroda, M.; Tvergaard, Viggo

    2008-01-01

    Recently, several higher-order extensions to the crystal plasticity theory have been proposed to incorporate effects of material length scales that were missing links in the conventional continuum mechanics. The extended theories are classified into work-conjugate and non-work-conjugate types...... backgrounds and very unlike mathematical representations. Nevertheless, both types of theories predict the same kind of material length scale effects. We have recently shown that there exists some equivalency between the two approaches in the special situation of two-dimensional single slip under small...

  14. Fast sweep-rate plastic Faraday force magnetometer with simultaneous sample temperature measurement.

    Science.gov (United States)

    Slobinsky, D; Borzi, R A; Mackenzie, A P; Grigera, S A

    2012-12-01

    We present a design for a magnetometer capable of operating at temperatures down to 50 mK and magnetic fields up to 15 T with integrated sample temperature measurement. Our design is based on the concept of a Faraday force magnetometer with a load-sensing variable capacitor. A plastic body allows for fast sweep rates and sample temperature measurement, and the possibility of regulating the initial capacitance simplifies the initial bridge balancing. Under moderate gradient fields of ~1 T/m our prototype performed with a resolution better than 1 × 10(-5) emu. The magnetometer can be operated either in a dc mode, or in an oscillatory mode which allows the determination of the magnetic susceptibility. We present measurements on Dy(2)Ti(2)O(7) and Sr(3)Ru(2)O(7) as an example of its performance.

  15. Shrinkage strainRates study of dental composites based on (BisGMA/TEGDMA monomers

    Directory of Open Access Journals (Sweden)

    A. Amirouche-Korichi

    2017-02-01

    The results revealed that the fraction of opaque filler had no significant effect on the shrinkage strain-rate and on the time at maximum shrinkage strain-rate but these two parameters are closely related to the monomer ratios and viscosity of the organic matrix. The results have confirmed the proportionality of the shrinkage strain and DC and showed that the filler contents and monomer ratios would not affect this proportionality.

  16. Bulk Nanolayered Composites: Interfacial Influence on Microstructural Evolution at Large Plastic Strains

    Energy Technology Data Exchange (ETDEWEB)

    Mara, Nathan A. [Los Alamos National Laboratory; Carpenter, John S. [Los Alamos National Laboratory; Han, Weizhong [Los Alamos National Laboratory; Zheng, Shijian [Los Alamos National Laboratory; McCabe, Rodney J. [Los Alamos National Laboratory; Wang, Jian [Los Alamos National Laboratory; Beyerlein, Irene J. [Los Alamos National Laboratory

    2012-07-31

    Conclusions are: (1) As-processed ARB material has similar morphology, chemistry as PVD, but different interfacial structure; (2) Density of interfaces AND interfacial structure play a role in determining hardness, an example is twinning in Cu at the {l_brace}112{r_brace}Cu//{l_brace}112{r_brace}Nb interface and higher strength, no twinning in Cu in the {l_brace}111{r_brace}Cu//{l_brace}110{r_brace}Nb interface; and (3) Need to understand effects of processing history to predict the effects on the interfaces we produce - Amount of strain, Strain Path, Annealing.

  17. The Effect of Strain Rate on Tensile Properties of Cotton Yarns

    Institute of Scientific and Technical Information of China (English)

    石风俊; 崔世忠

    2003-01-01

    The effect of strain rate on tensile properties of cotton yarns is analyzed using the standard linear solid model. The tensile curve, breaking strength and work of rupture of the yarns under different strain rate are calculated. A good correlation exists between the experiment results and theoretical anticipations.

  18. High Strain Rate Characterization of Shock Absorbing Materials for Landmine Protection Concepts

    Directory of Open Access Journals (Sweden)

    Jennifer McArthur

    2003-01-01

    Full Text Available Numerical modelling of footwear to protect against anti-personnel landmines requires dynamic material properties in the appropriate strain rate regime to accurately simulate material response. Several materials (foamed metals, honeycombs and polymers are used in existing protective boots, however published data at high strain rates is limited.

  19. Strain rates of opening-mode fractures in deep basinal settings

    Science.gov (United States)

    Eichhubl, Peter; Hooker John, N.; Andras, Fall; Laubach Stephen, E.

    2010-05-01

    Long-term strain rates for geologic processes are characteristically in the range of 10-13 to 10-17 s-1 as measured by a variety of techniques, including geodetic techniques, radiometric dating of tectonic and structural processes, and through stratigraphic correlations. Here, we present strain rates for populations of opening-mode fractures in sandstone in deep basinal settings. Fracture strain is obtained by collecting aperture-frequency data for microfractures along scanlines in weakly deformed sandstone. Opening durations of individual macrofractures in the same population are then obtained through detailed microthermometry of fluid inclusions in crack-seal fracture cement, combined with textural reconstructions of the fracture opening history. Temperature data are then correlated with known burial history models to obtain the duration of fracture opening and the fracture opening strain rate. Individual fractures in deeply buried sandstone of the East Texas basin, a passive margin setting, opened over 48 m.y. with a strain rate of 2x10-18 s-1to 5x10-19 s-1. Similar strain rates are obtained for fractures in the Piceance intermontane basin of Colorado. These ultraslow strain rates compare well to longterm intraplate seismic strain rates suggesting that rates of fracture opening are controlled by intraplate tectonic deformation processes.

  20. The strain-rate sensitivity of high-strength high-toughness steels.

    Energy Technology Data Exchange (ETDEWEB)

    Dilmore, M.F. (AFRL/MNMW, Eglin AFB, FL); Crenshaw, Thomas B.; Boyce, Brad Lee

    2006-01-01

    The present study examines the strain-rate sensitivity of four high strength, high-toughness alloys at strain rates ranging from 0.0002 s-1 to 200 s-1: Aermet 100, a modified 4340, modified HP9-4-20, and a recently developed Eglin AFB steel alloy, ES-1c. A refined dynamic servohydraulic method was used to perform tensile tests over this entire range. Each of these alloys exhibit only modest strain-rate sensitivity. Specifically, the strain-rate sensitivity exponent m, is found to be in the range of 0.004-0.007 depending on the alloy. This corresponds to a {approx}10% increase in the yield strength over the 7-orders of magnitude change in strain-rate. Interestingly, while three of the alloys showed a concominant {approx}3-10% drop in their ductility with increasing strain-rate, the ES1-c alloy actually exhibited a 25% increase in ductility with increasing strain-rate. Fractography suggests the possibility that at higher strain-rates ES-1c evolves towards a more ductile dimple fracture mode associated with microvoid coalescence.

  1. High-strain-rate tensile mechanical response of a polyurethane elastomeric material

    NARCIS (Netherlands)

    Fan, J.T.; Weerheijm, J.; Sluys, L.J.

    2015-01-01

    The dynamic tensile mechanical response of a soft polymer material (Clear Flex 75) is investigated using a split Hopkinson tension bar (SHTB). Stress-strain relations are derived to reveal the mechanical properties at moderate and high strain rates. These relations appear to be rate dependent. Under

  2. Dynamic High-Temperature Characterization of an Iridium Alloy in Compression at High Strain Rates

    Energy Technology Data Exchange (ETDEWEB)

    Song, Bo [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Experimental Environment Simulation Dept.; Nelson, Kevin [Sandia National Lab. (SNL-CA), Livermore, CA (United States). Mechanics of Materials Dept.; Lipinski, Ronald J. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Advanced Nuclear Fuel Cycle Technology Dept.; Bignell, John L. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Structural and Thermal Analysis Dept.; Ulrich, G. B. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Radioisotope Power Systems Program; George, E. P. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Radioisotope Power Systems Program

    2014-06-01

    Iridium alloys have superior strength and ductility at elevated temperatures, making them useful as structural materials for certain high-temperature applications. However, experimental data on their high-temperature high-strain-rate performance are needed for understanding high-speed impacts in severe elevated-temperature environments. Kolsky bars (also called split Hopkinson bars) have been extensively employed for high-strain-rate characterization of materials at room temperature, but it has been challenging to adapt them for the measurement of dynamic properties at high temperatures. Current high-temperature Kolsky compression bar techniques are not capable of obtaining satisfactory high-temperature high-strain-rate stress-strain response of thin iridium specimens investigated in this study. We analyzed the difficulties encountered in high-temperature Kolsky compression bar testing of thin iridium alloy specimens. Appropriate modifications were made to the current high-temperature Kolsky compression bar technique to obtain reliable compressive stress-strain response of an iridium alloy at high strain rates (300 – 10000 s-1) and temperatures (750°C and 1030°C). Uncertainties in such high-temperature high-strain-rate experiments on thin iridium specimens were also analyzed. The compressive stress-strain response of the iridium alloy showed significant sensitivity to strain rate and temperature.

  3. Modeling of failure mode in knee ligaments depending on the strain rate

    Directory of Open Access Journals (Sweden)

    Hyman William

    2002-01-01

    Full Text Available Abstract Background The failure mechanism of the knee ligament (bone-ligament-bone complex at different strain rates is an important subject in the biomechanics of the knee. This study reviews and summarizes the literature describing ligament injury as a function of stain rate, which has been published during the last 30 years. Methods Three modes of injury are presented as a function of strain rate, and they are used to analyze the published cases. The number of avulsions is larger than that of ligament tearing in mode I. There is no significant difference between the number of avulsions and ligament tearing in mode II. Ligament tearing happens more frequently than avulsion in mode III. Results When the strain rate increases, the order of mode is mode I, II, III, I, and II. Analytical models of ligament behavior as a function of strain rate are also presented and used to provide an integrated framework for describing all of the failure regimes. In addition, this study showed the failure mechanisms with different specimens, ages, and strain rates. Conclusion There have been several a numbers of studies of ligament failure under various conditions including widely varying strain rates. One issue in these studies is whether ligament failure occurs mid-ligament or at the bone attachment point, with assertions that this is a function of the strain rate. However, over the range of strain rates and other conditions reported, there has appeared to be discrepancies in the conclusions on the effect of strain rate. The analysis and model presented here provides a unifying assessment of the previous disparities, emphasizing the differential effect of strain rate on the relative strengths of the ligament and the attachment.

  4. A strain gradient crystal plasticity analysis of grain size effects in polycrystals

    DEFF Research Database (Denmark)

    Borg, Ulrik

    2007-01-01

    individually oriented grains, in a unit cell, each having three planar slip systems. An energy potential that penalizes crystallographic slip at grain boundaries is included in the analyzes. The polycrystal is subjected to plane strain tension for various grain sizes and higher order boundary conditions...

  5. Numerical simulation of elasto-plastic electro-osmosis consolidation at large strain

    NARCIS (Netherlands)

    Yuan, J.; Hicks, M.A.

    2015-01-01

    n this paper, a numerical solution for the electro-osmosis consolidation of clay in multi-dimensional domains at large strains is presented, with the coupling of the soil mechanical behaviour, pore water transport and electrical fields being considered. In particular, the Modified Cam Clay model is

  6. Effect of large elastic strains on cavitation instability predictions for elastic-plastic solids

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    1999-01-01

    For an infinite solid containing a void, the cavitation instability limit is defined as the remote stress-and strain state, at which the void grows without bound, driven by the elastic energy stored in the surrounding material. Such cavitation limits have been analysed by a number of authors...

  7. Numerical simulation of elasto-plastic electro-osmosis consolidation at large strain

    NARCIS (Netherlands)

    Yuan, J.; Hicks, M.A.

    2015-01-01

    n this paper, a numerical solution for the electro-osmosis consolidation of clay in multi-dimensional domains at large strains is presented, with the coupling of the soil mechanical behaviour, pore water transport and electrical fields being considered. In particular, the Modified Cam Clay model is

  8. A new approach for elasto-plastic finite strain analysis of cantilever beams subjected to uniform bending moment

    Indian Academy of Sciences (India)

    GOKHAN T TAYYAR

    2016-04-01

    The reliability and limits of solutions for static structural analysis depend on the accuracy of the curvature and deflection calculations. Even if the material model is close to the actual material behavior, physically unrealistic deflections or divergence problems are unavoidable in the analysis if an appropriate fundamental kinematic theory is not chosen. Moreover, accurate deflection calculation plays an important role in ultimate strength analysis where in-plane stresses are considered. Therefore, a more powerful method is neededto achieve reliable deflection calculation and modeling. For this purpose, a new advanced step was developed by coupling the elasto-plastic material behavior with precise general planar kinematic analysis. The deflection is generated precisely without making geometric assumptions or using differential equations of the deflection curve. An analytical finite strain solution was derived for an elasto-plastic prismatic/non-prismatic rectangular cross-sectioned beam under a uniform moment distribution. A comparison of the analytical results with thosefrom the Abaqus FEM software package reveals a coherent correlation.

  9. Inelastic strain rate in the seismogenic layer of Kyushu Island, Japan

    Science.gov (United States)

    Matsumoto, Satoshi; Nishimura, Takuya; Ohkura, Takahiro

    2016-12-01

    Seismic activity is associated with crustal stress relaxation, creating inelastic strain in a medium due to faulting. Inelastic strain affects the stress field around a weak body and causes stress concentration around the body, because the body itself has already released stress. Therefore, the understanding of inelastic deformation is important as it generates earthquakes. We investigated average inelastic strain in a spatial bin of Kyushu Island, Japan, and obtained the inelastic strain rate distribution associated with crustal earthquakes, based on the analysis of fault plane solutions and seismic moments. Large inelastic strains (>10-7 year-1) were found in the Beppu-Shimabara area, located in the center of Kyushu Island. The strain rate tensor was similar to that of the stress tensor except the absolute value in the area, implying that the inelastic strain was controlled by the stress field. The 2016 Kumamoto earthquake sequence (maximum magnitude 7.3) occurred in the Beppu-Shimabara area, with the major earthquakes located around the high inelastic strain rate area. Inelastic strain in the volume released the stress. In addition, the inelastic strain created an increment of stress around the volume. This indicates that the spatial heterogeneity of inelastic strain might concentrate stress.[Figure not available: see fulltext.

  10. TRIP effect in austenitic-martensitic VNS9-Sh steel at various strain rates

    Science.gov (United States)

    Terent'ev, V. F.; Slizov, A. K.; Prosvirnin, D. V.

    2016-10-01

    The mechanical properties of austenitic-martensitic VNS9-Sh (23Kh15N5AM3-Sh) steel are studied at a static strain rate from 4.1 × 10-5 to 17 × 10-3 s-1 (0.05-20 mm/min). It is found that, as the strain rate increases, the ultimate tensile strength decreases and the physical yield strength remains unchanged (≈1400 MPa). As the strain rate increases, the yield plateau remains almost unchanged and the relative elongation decreases continuously. Because of high microplastic deformation, the conventional yield strength is lower than the physical yield strength over the entire strain rate range under study. The influence of the TRIP effect on the changes in the mechanical properties of VNS9-Sh steel at various strain rates is discussed.

  11. Slow Strain Rate Tensile Testing to Assess the Ability of Superalloys to Resist Environment-Assisted Intergranular Cracking

    Science.gov (United States)

    Gabb, Timothy P.; Telesman, Jack; Banik, Anthony; McDevitt, Erin

    2014-01-01

    Intergranular fatigue crack initiation and growth due to environmental degradation, especially at notched features, can often limit the fatigue life of disk superalloys at high temperatures. For clear comparisons, the effects of alloy composition on cracking in air needs to be understood and compared separately from variables associated with notches and cracks such as effective stress concentration, plastic flow, stress relaxation, and stress redistribution. The objective of this study was to attempt using simple tensile tests of specimens with uniform gage sections to compare the effects of varied alloy composition on environment-assisted cracking of several powder metal and cast and wrought superalloys including ME3, LSHR, Udimet 720, ATI 718Plus alloy, Haynes 282, and Inconel 740. Slow and fast strain-rate tensile tests were found to be a useful tool to compare propensities for intergranular surface crack initiation and growth. The effects of composition and heat treatment on tensile fracture strain and associated failure modes were compared. Environment interactions were determined to often limit ductility, by promoting intergranular surface cracking. The response of various superalloys and heat treatments to slow strain rate tensile testing varied substantially, showing that composition and microstructure can significantly influence environmental resistance to cracking.

  12. Elastography and strain rate imaging of the gastrointestinal tract

    Energy Technology Data Exchange (ETDEWEB)

    Havre, R., E-mail: roald.flesland.havre@helse-bergen.no [National Centre for Ultrasound in Gastroenterology, Department of Medicine, Haukeland University Hospital, 5021 Bergen (Norway); Gilja, O.H. [National Centre for Ultrasound in Gastroenterology, Department of Medicine, Haukeland University Hospital, 5021 Bergen (Norway); Department of Clinical Medicine, University of Bergen, Bergen (Norway)

    2014-03-15

    Ultrasound based elastography of the gastrointestinal tract may be a useful approach to improved tissue characterisation. Distinguishing malignant lesions from benign may be one useful application. Monitoring of inflammatory bowel lesions for degree of inflammation or fibrosis would be another clinically useful tool. The anatomy of the bowel, however, raises many challenges for strain or shear wave imaging due to thin structures, non-constant boundary conditions and intrinsic contractility. Pathological lesions tend to increase bowel wall thickness and may ease elastography imaging. Very few studies have addressed issues of bowel wall elastography so far, and both inflammatory and neoplastic lesions seem to increase tissue hardness in the bowel wall.

  13. How to test brain and brain simulant at ballistic and blast strain rates.

    Science.gov (United States)

    Zhang, Jiangyue; Song, Bo; Pintar, Frank A; Yoganandan, Narayan; Chen, Weinong; Gennarelli, Thomas A

    2008-01-01

    Mechanical properties of brain tissue and brain simulant at strain rate in the range of 1000 s-1 are essential for computational simulation of intracranial responses for ballistic and blast traumatic brain injury. Testing these ultra-soft materials at high strain rates is a challenge to most conventional material testing methods. The current study developed a modified split Hopkinson bar techniques using the combination of a few improvements to conventional split Hopkinson bar including: using low impedance aluminum bar, semiconductor strain gauge, pulse shaping technique and annular specimen. Feasibility tests were conducted using a brain stimulant, Sylgard 527. Stress-strain curves of the simulant were successfully obtained at strain rates of 2600 and 2700 s-1 for strain levels up to 60%. This confirmed the applicability of Hopkinson bar for mechanical properties testing of brain tissue in the ballistic and blast domain.

  14. High Strain Rate Compression of Martensitic NiTi Shape Memory Alloy at Different Temperatures

    Science.gov (United States)

    Qiu, Ying; Young, Marcus L.; Nie, Xu

    2017-02-01

    The compressive response of martensitic NiTi shape memory alloy (SMA) rods has been investigated using a modified Kolsky compression bar at various strain rates (400, 800, and 1200 s-1) and temperatures [room temperature and 373 K (100 °C)], i.e., in the martensitic state and in the austenitic state. SEM, DSC, and XRD were performed on NiTi SMA rod samples after high strain rate compression in order to reveal the influence of strain rate and temperature on the microstructural evolution, phase transformation, and crystal structure. It is found that at room temperature, the critical stress increases slightly as strain rate increases, whereas the strain-hardening rate decreases. However, the critical stress under high strain rate compression at 373 K (100 °C) increase first and then decrease due to competing strain hardening and thermal softening effects. After high rate compression, the microstructure of both martensitic and austenitic NiTi SMAs changes as a function of increasing strain rate, while the phase transformation after deformation is independent of the strain rate at room temperature and 373 K (100 °C). The preferred crystal plane of the martensitic NiTi SMA changes from ( 1bar{1}1 )M before compression to (111)M after compression, while the preferred plane remains the same for austenitic NiTi SMA before and after compression. Additionally, dynamic recovery and recrystallization are also observed to occur after deformation of the austenitic NiTi SMA at 373 K (100 °C). The findings presented here extend the basic understanding of the deformation behavior of NiTi SMAs and its relation to microstructure, phase transformation, and crystal structure, especially at high strain rates.

  15. Mechanical behavior of a lanthanum-doped magnesium alloy at different strain rates

    Energy Technology Data Exchange (ETDEWEB)

    Shen, J. [Department of Mechanical Engineering, University of North Carolina at Charlotte, Charlotte, NC 28223-0001 (United States); School of Aeronautics, Northwestern Polytechnical University, Xi’an 710072 (China); Yin, W. [Department of Mechanical Engineering, University of North Carolina at Charlotte, Charlotte, NC 28223-0001 (United States); Kondoh, K. [Joining and Welding Research Institute, Osaka University, 11-1 Mihogaoka, Ibaragi, Osaka 567-0047 (Japan); Jones, Tyrone L.; Kecskes, L.J. [WMRD, US Army Research Laboratory, Aberdeen Proving Ground, Deer Creek Loop, Aberdeen Proving Ground, MD 21005-5069 (United States); Yarmolenko, S.N. [NSF-ERC, Department of Mechanical Engineering, NC A& T State University, 1601 E. Market Street, Greensboro, NC 27411 (United States); Wei, Q., E-mail: qwei@uncc.edu [Department of Mechanical Engineering, University of North Carolina at Charlotte, Charlotte, NC 28223-0001 (United States)

    2015-02-25

    The mechanical behavior of a lanthanum doped Mg alloy, AZXE7111, (Mg–7Al–1Zn–1Ca–1La, all in wt%) extruded at different temperatures has been investigated under both quasi-static (strain rate ~1×10{sup −3} s{sup −1}) and dynamic (strain rate ~4×10{sup 3} s{sup −1}) compressive loading. Comparison has been made against the experimental results of two conventional Mg alloys, AZ91E and WE43. It was observed via transmission electron microscopy (TEM) that the nanoscale intermetallic compounds of Al{sub 2}Ca and Al{sub 11}La{sub 3}, have presumably formed during the hot extrusion process. These compounds are believed to contribute significantly to the strength by reducing the grain size and acting as dislocation barriers. Additionally, twinning has been considered as the main mechanism for the higher strain hardening rate at high strain rates than that at low strain rates. It has been found that the ultimate strength of the alloy is only ~10% higher at dynamic loading rate than at quasi-static loading rate. Localized micro-shear fracture was observed and adiabatic shear mode was suggested by further examination of dynamically loaded specimens. The shear localization is further discussed in detail and it is suggested that reduced strain hardening rate is responsible for shear localization and subsequent fracture at both low and high strain rates.

  16. The Flo11p-deficient Saccharomyces cerevisiae strain background S288c can adhere to plastic surfaces

    DEFF Research Database (Denmark)

    Mortensen, Henrik Dam; Dupont, Kitt; Jespersen, Lene;

    2007-01-01

    The effects of four types of plastic surfaces and four pre-incubation media, containing high/low glucose and +/- amino acids, on adhesion of Saccharomyces cerevisiae BY4742 wild type and Deltaflo11 mutant (strain background S288c) were investigated. No difference in adhesive ability between the two...... yeast strains was observed in any of our experiments, thus confirming that FLO11 is not operational in the S. cerevisiae S288c strain background. The adhesive abilities of both yeast strains depended on the plastic type and pre-incubation conditions. The poorest adhesion was observed on hydrophilic...... hydrophobicity and enhanced the adhesion to all four types of polystyrene. Lack of amino acids in the pre-incubation media increased the cell surface hydrophobicity and enhanced the adhesion especially to polystyrene surfaces with combined hydrophilic/hydrophobic domains. Our results suggest that glucose...

  17. Strain Rate Dependence of Compressive Yield and Relaxation in DGEBA Epoxies

    Science.gov (United States)

    Arechederra, Gabriel K.; Reprogle, Riley C.; Clarkson, Caitlyn M.; McCoy, John D.; Kropka, Jamie M.; Long, Kevin N.; Chambers, Robert S.

    2015-03-01

    The mechanical response in uniaxial compression of two diglycidyl ether of bisphenol-A epoxies were studied. These were 828DEA (Epon 828 cured with diethanolamine (DEA)) and 828T403 (Epon 828 cured with Jeffamine T-403). Two types of uniaxial compression tests were performed: A) constant strain rate compression and B) constant strain rate compression followed by a constant strain relaxation. The peak (yield) stress was analyzed as a function of strain rate from Eyring theory for activation volume. Runs at different temperatures permitted the construction of a mastercurve, and the resulting shift factors resulted in an activation energy. Strain and hold tests were performed for a low strain rate where a peak stress was lacking and for a higher strain rate where the peak stress was apparent. Relaxation from strains at different places along the stress-strain curve was tracked and compared. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  18. Experimental study of dynamic mechanical properties of reactive powder concrete under high-strain-rate impacts

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The dynamic mechanical properties of reactive powder concrete subjected to compressive impacts with high strain rates ranging from 10 to 1.1×102 s-1 were investigated by means of SHPB (split-Hopkinson-pressure-bar) tests of the cylindrical specimens with five different steel fiber volumetric fractions.The properties of wave stress transmission,failure,strength,and energy consumption of RPC with varied fiber volumes and impact strain rates were analyzed.The influences of impact strain rates and fiber volumes on those properties were characterized as well.The general forms of the dynamic stress-strain relationships of RPC were modeled based on the experimental data.The investigations indicate that for the plain RPC the stress response is greater than the strain response,showing strong brittle performance.The RPC with a certain volume of fibers sustains higher strain rate impact and exhibits better deformability as compared with the plain RPC.With a constant fiber fraction,the peak compressive strength,corresponding peak strain and the residual strain of the fiber-reinforced RPC rise by varying amounts when the impact strain rate increases,with the residual strain demonstrating the greatest increment.Elevating the fiber content makes trivial contribution to improving the residual deformability of RPC when the impact strain rate is constant.The tests also show that the fiber content affects the peak compressive strength and the peak deformability of RPC in a different manner.With a constant impact strain rate and the fiber fraction less than 1.75%,the peak compressive strength rises with an increasing fiber volume.The peak compressive strength tends to decrease as the fiber volume exceeds 1.75%.The corresponding peak strain,however,incessantly rises with the increasing fiber volume.The total energy Edisp that RPC consumed during the period from the beginning of impacts to the time of residual strains elevates with the fiber volume increment as long as the fiber

  19. Strain and strain rate by two-dimensional speckle tracking echocardiography in a maned wolf Strain e strain rate por meio de ecocardiogratia speckle traking bidimensional em um lobo-guará

    Directory of Open Access Journals (Sweden)

    Matheus M. Mantovani

    2012-12-01

    Full Text Available The measurement of cardiovascular features of wild animals is important, as is the measurement in pets, for the assessment of myocardial function and the early detection of cardiac abnormalities, which could progress to heart failure. Speckle tracking echocardiography (2D STE is a new tool that has been used in veterinary medicine, which demonstrates several advantages, such as angle independence and the possibility to provide the early diagnosis of myocardial alterations. The aim of this study was to evaluate the left myocardial function in a maned wolf by 2D STE. Thus, the longitudinal, circumferential and radial strain and strain rate were obtained, as well as, the radial and longitudinal velocity and displacement values, from the right parasternal long axis four-chamber view, the left parasternal apical four chamber view and the parasternal short axis at the level of the papillary muscles. The results of the longitudinal variables were -13.52±7.88, -1.60±1.05, 4.34±2.52 and 3.86±3.04 for strain (%, strain rate (1/s, displacement (mm and velocity (cm/s, respectively. In addition, the radial and circumferential Strain and Strain rate were 24.39±14.23, 1.86±0.95 and -13.69±6.53, -1.01±0.48, respectively. Thus, the present study provides the first data regarding the use of this tool in maned wolves, allowing a more complete quantification of myocardial function in this species.A obtenção de parâmetros cardiovasculares em animais selvagens são importantes de serem avaliados, assim como em animais de companhia, para a obtenção da função miocárdica e determinação precoce de alterações cardíacas que poderiam evoluir para insuficiência cardíaca . A ecocardiografia speckle tracking (2D STE é uma ferramenta nova que tem sido utilizada em medicina veterinária, a qual tem demonstrado várias vantagens quanto ao seu uso, como a independência do ângulo de insonação e a possibilidade de se obter o diagnóstico precoce de altera

  20. Assessment of left ventricular functions with tissue Doppler, strain, and strain rate echocardiography in patients with familial Mediterranean fever.

    Science.gov (United States)

    Ceylan, Özben; Özgür, Senem; Örün, Utku Arman; Doğan, Vehbi; Yılmaz, Osman; Keskin, Mahmut; Arı, Mehmet Emre; Erdoğan, Özlem; Karademir, Selmin

    2015-08-01

    This study assessed the early changes in regional and global systolic and diastolic myocardial functions in patients with familial Mediterranean fever without any cardiovascular symptoms using tissue Doppler and strain and strain rate echocardiography and compared them to the results of a control group. This study has a cross-sectional and observational design. FMF patients with normal left ventricular function were included in the study. We excluded patients who had arrhythmia, acquired/congenital heart disease, pericarditis, or acute attack. We compared 45 children with familial Mediterranean fever on colchicine therapy and 45 age- and sex-matched healthy children. The 45 patients with familial Mediterranean fever included 24 (55.3%) girls and 21 (46.7%) boys with a mean age of 11.3 ± 3.7 (range 2-18) years. The mean disease duration was 4.6 ± 2.4 (range 0.5-10) years. In the patient group, the homozygous M694V mutation was the most common (64.4%) mutation. The patients with familial Mediterranean fever had statistically lower longitudinal global strain, radial global strain, and strain rates (-14.44 ± 4.77%, 14.80 ± 6.29%, and 0.59 ± 0.24 s, respectively) than the controls (-17.40 ± 1.79%, 17.53 ± 4.63%, and 0.83 ± 0.51 s) (p familial Mediterranean fever who are subclinical from a cardiac aspect might have normal left ventricular function as measured by conventional echocardiography. However, the disease affects their myocardial tissue, and these patients should be followed with conventional, strain, and strain rate echocardiography techniques regularly.

  1. Studies on Dynamic Damage Evolution for Pp/pa Polymer Blends Under High Strain Rates

    Science.gov (United States)

    Sun, Zi-Jian; Wang, Li-Li

    The dynamic damage evolution for PP/PA blends with different compatibilizers is studied in high strain rates from two different approaches, namely by determining the unloading elastic modulus of specimen experienced impact deformation and by combining the split Hopkinson pressure bar (SHPB) experimental technique with the back-propagation (BP) neural network. The results obtained by both approaches consistently show that a threshold strain ɛth exists for dynamic damage evolution, and both the damage evolution and ɛth are dependent on strain and strain rate. For non-linear visco-elastic materials, the damage evolution determined by the unloading elastic modulus provides an underestimation of real damage evolution.

  2. Constitutive equations of basalt filament tows under quasi-static and high strain rate tension

    Energy Technology Data Exchange (ETDEWEB)

    Zhu Lvtao; Sun Baozhong [College of Textiles, Donghua University, Shanghai 201620 (China); Hu, Hong [Institute of Textiles and Clothing, Hong Kong Polytechnic University, Hung Hom Kowloon (Hong Kong); Gu Bohong, E-mail: gubh@dhu.edu.cn [College of Textiles, Donghua University, Shanghai 201620 (China); Department of Textile Engineering, Zhongyuan Institute of Technology, Zhengzhou, Henan Province 450007 (China)

    2010-05-25

    The tensile properties of basalt filament tows were tested at quasi-static (0.001 s{sup -1}) and high strain rates (up to 3000 s{sup -1}) with MTS materials tester (MTS 810.23) and split Hopkinson tension bar (SHTB), respectively. Experimental results showed that the mechanical properties of the basalt filament tows were rather sensitive to strain rate. Specifically, the stiffness and failure stress of the basalt filament tows increased distinctly as the strain rate increased, while the failure strain decreased. From scanning electronic microscope (SEM) photographs of the fracture surface, it is indicated that the basalt filament tows failed in a more brittle mode and the fracture surface got more regular as the strain rate increases. The strength distributions of the basalt filament tows have been evaluated by a single Weibull distribution function. The curve predicted from the single Weibull distribution function was in good agreement with the experimental data points.

  3. Effects of Temperature and Strain Rate on Dynamic Properties of Concrete

    Institute of Scientific and Technical Information of China (English)

    JIA Bin; TAO Junlin; LI Zhengliang; WANG Ruheng; ZHANG Yu

    2008-01-01

    To study the dynamic properties of the concrete subjected to impulsive loading,stress-time curves of concrete in different velocities were measured using split Hopkinson pressure bar (SHPB).Effects of temperature and strain rate on the dynamic yield strength and constitutive relation of the concrete were analyzed.The dynamic mechanical properties of the reinforced concrete are subjected to high strain rates when it is at a relatively low temperature.But with temperature increasing,the temperature softening effect makes the strength of the concrete weaken and the impact toughness of the concrete is saliently relative to strain rate effect.So,strain rate effect,strain hardening and temperature softening work together on the dynamic mechanical capability of concrete and the relation between them is relatively corn plex.

  4. STIR: Tailored Interfaces for High Strength Composites Across Strain Rates

    Science.gov (United States)

    2013-09-02

    was requested during our kickoff meeting at ARL APG. High performance fabrics including Kevlar, Twaron, Zylon , and Dyneema are used in developing...Kevlar, and Zylon for various pullout rates. Force– displacement data was recorded, and both warp and fill yarns were pulled from the fabric. Their...results presented that the effect of pullout rate is negligible for Kevlar, whereas the effect is bigger on Spectra, and significant for Zylon

  5. Prediction of flow stress of 7017 aluminium alloy under high strain rate compression at elevated temperatures

    Institute of Scientific and Technical Information of China (English)

    Ravindranadh BOBBILI; B. RAMAKRISHNA; V. MADHU; A.K. GOGIA

    2015-01-01

    An artificial neural network (ANN) constitutive model and JohnsoneCook (JeC) model were developed for 7017 aluminium alloy based on high strain rate data generated from split Hopkinson pressure bar (SHPB) experiments at various temperatures. A neural network configuration consists of both training and validation, which is effectively employed to predict flow stress. Temperature, strain rate and strain are considered as inputs, whereas flow stress is taken as output of the neural network. A comparative study on JohnsoneCook (JeC) model and neural network model was performed. It was observed that the developed neural network model could predict flow stress under various strain rates and tem-peratures. The experimental stressestrain data obtained from high strain rate compression tests using SHPB over a range of temperatures (25?e300 ?C), strains (0.05e0.3) and strain rates (1500e4500 s?1) were employed to formulate JeC model to predict the flow stress behaviour of 7017 aluminium alloy under high strain rate loading. The JeC model and the back-propagation ANN model were developed to predict the flow stress of 7017 aluminium alloy under high strain rates, and their predictability was evaluated in terms of correlation coefficient (R) and average absolute relative error (AARE). R and AARE for the J-C model are found to be 0.8461 and 10.624%, respectively, while R and AARE for the ANN model are 0.9995 and 2.58%, respectively. The predictions of ANN model are observed to be in consistent with the experimental data for all strain rates and temperatures.

  6. High Strain and Strain-Rate Behaviour of Ptfe/aluminuim/tungsten Mixtures

    Science.gov (United States)

    Addiss, John; Cai, Jing; Walley, Stephen; Proud, William; Nesterenko, Vitali

    2007-12-01

    Conventional drop-weight techniques were modified to accommodate low-amplitude force transducer signals from low-strength, cold isostatically pressed `heavy' composites of polytetrafluoroethylene, aluminum and tungsten (W). The failure strength, strain and the post-critical behavior of failed samples were measured for samples of different porosity and tungsten grain size. Unusual phenomenon of significantly higher strength (55 MPa) of porous composites (density 5.9 g/cm3) with small W particles (compression.

  7. Dynamic Strength and Accumulated Plastic Strain Development Laws and Models of the Remolded Red Clay under Long-Term Cyclic Loads: Laboratory Test Results

    Directory of Open Access Journals (Sweden)

    Li Jian

    2015-09-01

    Full Text Available The dynamic strength and accumulated plastic strain are two important parameters for evaluating the dynamic response of soil. As a special clay, the remolded red clay is often used as the high speed railway subgrade filling, but studies on its dynamic characteristics are few. For a thorough analysis of the suitability of the remolded red clay as the subgrade filling, a series of long-term cyclic load triaxial test under different load histories are carried out. Considering the influence of compactness, confining pressure, consolidation ratio, vibration frequency and dynamic load to the remolded red clay dynamic property, the tests obtain the development curves of the dynamic strength and accumulated plastic strain under different test conditions. Then, through curve fitting method, two different hyperbolic models respectively for the dynamic strength and accumulated plastic strain are built, which can match the test datum well. By applying the dynamic strength model, the critical dynamic strength of the remolded red clay are gained. Meanwhile, for providing basic datum and reference for relevant projects, all key parameters for the dynamic strength and accumulated plastic strain of the remolded red clay are given in the paper.

  8. Investigation of Deformation Mechanisms in Deep-Drawn and Tensile-Strained Austenitic Mn-Based Twinning Induced Plasticity (TWIP) Steel

    NARCIS (Netherlands)

    Van Tol, R.T.; Zhao, L.; Schut, H.; Sietsma, J.

    2012-01-01

    The effect of strain on the deformation mechanisms in an austenitic Mn-based twinning induced plasticity (TWIP) steel is investigated using magnetic measurements, XRD, positron beam Doppler spectroscopy, and finite element method simulations. The experimental observations reveal the formation of a0-

  9. High-Strain Rate Tensile Behavior of Pure Aluminum Single and Multi-Crystalline Materials with a Tensile Split Hopkinson Bar

    Energy Technology Data Exchange (ETDEWEB)

    Ha, Sangyul [Samsung Electro-Mechanics, Suwon (Korea, Republic of); Jang, Jin Hee; Yoon, Hyo Jun; Kim, Ki Tae [Pohang Univ. of Science and Technology, Pohang (Korea, Republic of)

    2016-01-15

    In this study, we modified the conventional tensile split Hopkinson bar(TSHB) apparatus typically used for the high strength steel to evaluate the tensile deformation behavior of soft metallic sheet materials under high strain rates. Stress-strain curves of high purity single and multi-crystalline materials were obtained using this experimental procedure. Grain morphology and initial crystallographic orientation were characterized by EBSD(Electron Backscattered Diffraction) method measured in a FE-SEM(Field emission-scanning electron microscopy). The fractured surfaces were observed by using optical microscopy. The relationship between plastic deformation of aluminum crystalline materials under high-strain rates and the initial microstructure and the crystallographic orientations has been addressed.

  10. Thermomechanical Response of the Rotary Forged Wha Over a Wide Range of Strain Rates and Temperatures

    Science.gov (United States)

    Guo, W. G.; Qu, C.; Liu, F. L.

    This paper is to understand and model the thermomechanical response of the rotary forged WHA, uniaxial compression and tension tests are performed on cylindrical samples, using a material testing machines and the split Hopkinson bar technique. True strains exceeding 40% are achieved in these tests over the range of strain rates from 0.001/s to about 7,000/s, and at initial temperatures from 77K to 1,073K. The results show: 1) the WHA displays a pronounced changing orientation due to mechanical processing, that is, the material is inhomogeneous along the section; 2) the dynamic strain aging occurs at temperatures over 700K and in a strain rate of 10-3 1/s; 3) failure strains decrease with increasing strain rate under uniaxial tension, it is about 1.2% at a strain rate of 1,000 1/s; and 4) flow stress of WHA strongly depends on temperatures and strain rates. Finally, based on the mechanism of dislocation motion, the parameters of a physically-based model are estimated by the experimental results. A good agreement between the modeling prediction and experiments was obtained.

  11. Strain and plastic composite support (PCS) selection for vitamin K (Menaquinone-7) production in biofilm reactors.

    Science.gov (United States)

    Mahdinia, Ehsan; Demirci, Ali; Berenjian, Aydin

    2017-06-30

    Menaquinone-7 (MK-7), a subtype of vitamin K, has received a significant attention due to its effect on improving bone and cardiovascular health. Current fermentation strategies, which involve static fermentation without aeration or agitation, are associated with low productivity and scale-up issues and hardly justify the commercial production needs of this vitamin. Previous studies indicate that static fermentation is associated with pellicle and biofilm formations, which are critical for MK-7 secretion while posing significant operational issues. Therefore, the present study is undertaken to evaluate the possibility of using a biofilm reactor as a new strategy for MK-7 fermentation. Bacillus species, namely, Bacillus subtilis natto, Bacillus licheniformis, and Bacillus amyloliquifaciens as well as plastic composite, supports (PCS) were investigated in terms of MK-7 production and biofilm formation. Results show the possibility of using a biofilm reactor for MK-7 biosynthesis. Bacillus subtilis natto and soybean flour yeast extract PCS in glucose medium were found as the most potent combination for production of MK-7 as high as 35.5 mg/L, which includes both intracellular and extracellular MK-7.

  12. Effects of surface roughness on plastic strain localization in polycrystalline aggregates

    Directory of Open Access Journals (Sweden)

    Guilhem Yoann

    2014-06-01

    Full Text Available The surface state of mechanical components differs according to applied loadings. Industrial processes may produce specific features at the surface, such as roughness, local hardening, residual stresses or recrystallization. Under fatigue loading, all these parameters will affect the component lifetime, but in different manner. A better understanding of each surface state parameter, separately first and then all combined, will provide a better prediction of fatigue life. The study focuses on the effect of surface roughness. Crystal plasticity finite element computations have been carried out on three-dimensional polycrystalline aggregates with different roughness levels. Local mechanical fields have been analyzed both at the surface and inside the bulk to highlight the competition between crystallography and roughness to impose localization patterns. As soon as surface roughness is strong enough, classical localization bands driven by grains orientation are replaced by localizations patterns driven by the local roughness topology. Nevertheless, this effect tends to decrease gradually under the surface, and it becomes usually negligible after the first layer of grains. The discussion allows us to characterize the influence of the surface state on the local mechanical fields.

  13. Plastic equation of state determined by nano indentation

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    In order to characterize the plastic state of a deformed material, an indentation method to determine the plastic equation of state (PES) was developed. The work-hardening coefficient and the strain rate sensitivity coefficient of the plastic mechanic equation of state were determined by two kinds of indentation tests respectively. Therefore, the PES of materials under deformation can be obtained, and the plastic state of materials can be determined.

  14. Characteristic systolic waveform of left ventricular longitudinal strain rate in patients with hypertrophic cardiomyopathy.

    Science.gov (United States)

    Okada, Kazunori; Kaga, Sanae; Mikami, Taisei; Masauzi, Nobuo; Abe, Ayumu; Nakabachi, Masahiro; Yokoyama, Shinobu; Nishino, Hisao; Ichikawa, Ayako; Nishida, Mutsumi; Murai, Daisuke; Hayashi, Taichi; Shimizu, Chikara; Iwano, Hiroyuki; Yamada, Satoshi; Tsutsui, Hiroyuki

    2016-10-18

    We analyzed the waveform of systolic strain and strain-rate curves to find a characteristic left ventricular (LV) myocardial contraction pattern in patients with hypertrophic cardiomyopathy (HCM), and evaluated the utility of these parameters for the differentiation of HCM and LV hypertrophy secondary to hypertension (HT). From global strain and strain-rate curves in the longitudinal and circumferential directions, the time from mitral valve closure to the peak strains (T-LS and T-CS, respectively) and the peak systolic strain rates (T-LSSR and T-CSSR, respectively) were measured in 34 patients with HCM, 30 patients with HT, and 25 control subjects. The systolic strain-rate waveform was classified into 3 patterns ("V", "W", and "√" pattern). In the HCM group, T-LS was prolonged, but T-LSSR was shortened; consequently, T-LSSR/T-LS ratio was distinctly lower than in the HT and control groups. The "√" pattern of longitudinal strain-rate waveform was more frequently seen in the HCM group (74 %) than in the control (4 %) and HT (20 %) groups. Similar but less distinct results were obtained in the circumferential direction. To differentiate HCM from HT, the sensitivity and specificity of the T-LSSR/T-LS ratio waveform were 85 and 63 %, and 74 and 80 %, respectively. In conclusion, in patients with HCM, a reduced T-LSSR/T-LS ratio and a characteristic "√"-shaped waveform of LV systolic strain rate was seen, especially in the longitudinal direction. The timing and waveform analyses of systolic strain rate may be useful to distinguish between HCM and HT.

  15. Job strain in relation to ambulatory blood pressure, heart rate, and heart rate variability among female nurses

    NARCIS (Netherlands)

    Riese, H.; Doornen, L.J.P. van; Houtman, I.L.D.; Geus, E.J.C. de

    2004-01-01

    Objective. This study examined the effects of exposure to job strain on independent predictors of cardiovascular disease (ambulatory blood pressure, heart rate, and heart rate variability). Methods. The participants comprised a homogeneous group of 159 healthy female nurses [mean age 35.9 (SD 8.5)

  16. Job strain in relation to ambulatory blood pressure, heart rate, and heart rate variability among female nurses

    NARCIS (Netherlands)

    Riese, H.; Doornen, L.J.P. van; Houtman, I.L.D.; Geus, E.J.C. de

    2004-01-01

    Objective. This study examined the effects of exposure to job strain on independent predictors of cardiovascular disease (ambulatory blood pressure, heart rate, and heart rate variability). Methods. The participants comprised a homogeneous group of 159 healthy female nurses [mean age 35.9 (SD 8.5) y

  17. Cement-based composites: Strain rate effects on fracture

    Energy Technology Data Exchange (ETDEWEB)

    Mindess, S.; Shah, S.P.

    1986-01-01

    This book contains over 20 selections. Some of the titles are: Continuum damage mechanics studies on the dynamic fracture of concrete; Dynamic compressive strength of cementitious materials; Rate-sensitivity of mode I and mode II fracture concrete; and An impact damage model of concrete.

  18. Calculation of the Distribution Rule of Equivalent Strain Rate near Explosive Welding Interface

    Institute of Scientific and Technical Information of China (English)

    李晓杰; 闫鸿浩; 李瑞勇; 王金相

    2004-01-01

    The objectives of this study were to analyze the distribution of equivalent strain rate near the stagnation point and probe into the effects of colliding angle on strain rate. An ideal fluid model of symmetrically colliding was used to research them. Calculations showed the equivalent strain rate and the colliding half angle are closely related to each other with the material geometrical size and explosive velocity selected, the equivalent strain has large gradient within several jet thicknesses near the stagnation point, the maximal strain points are lined up along a beeline, but a curve near the stagnation point. With different colliding angles, they can be fitted by using exponential curve. That is, the exponential curve can be regarded as the token curve in explosive welding.

  19. High strain rate tensile behavior of Al-4.8Cu-1.2Mg alloy

    Energy Technology Data Exchange (ETDEWEB)

    Bobbili, Ravindranadh, E-mail: ravindranadh@dmrl.drdo.in; Paman, Ashish; Madhu, V.

    2016-01-10

    The purpose of the current study is to perform quasi static and high strain rate tensile tests on Al-4.8Cu-1.2Mg alloy under different strain rates ranging from 0.01–3500/s and also at temperatures of 25,100, 200 and 300 °C. The combined effect of strain rate, temperature and stress triaxiality on the material behavior is studied by testing both smooth and notched specimens. Johnson–Cook (J–C) constitutive and fracture models are established based on high strain rate tensile data obtained from Split hopkinson tension bar (SHTB) and quasi-static tests. By modifying the strain hardening and strain rate hardening terms in the Johnson–Cook (J–C) constitutive model, a new J–C constitutive model of Al-4.8Cu-1.2Mg alloy was obtained. The improved Johnson–Cook constitutive model matched the experiment results very well. With the Johnson–Cook constitutive and fracture models, numerical simulations of tensile tests at different conditions for Al-4.8Cu-1.2Mg alloy were conducted. Numerical simulations are performed using a non-linear explicit finite element code autodyn. Good agreement is obtained between the numerical simulation results and the experiment results. The fracture surfaces of specimens tested under various strain rates and temperatures were studied under scanning electron microscopy (SEM).

  20. Modeling temperature and strain rate history in effects in OFHU Cu

    Science.gov (United States)

    Tanner, Albert Buck

    Accurate material behavior prediction during large deformations is essential. For the U.S. Army, explosively formed projectiles (EFP), penetrators, and vehicle armor are applications which will benefit from a better understanding of and ability to predict material behavior when subjected to high and varying strain rates and temperatures. Linking macro-scale material behavior with the evolution of microstructure has proven effective in obtaining an appropriate mathematical structure for constitutive relationships. Incorporation of strain rate, temperature, and deformation path history effects are especially critical to accurately predict material responses for arbitrary nonisothermal, variable strain rate conditions. Material constitutive equations contain numerous parameters which must be determined experimentally, and often are not fully optimized. The goal of this research was to develop more physically descriptive kinematics and kinetics models for large strain deformation based on internal state variable (ISV) evolution laws which include strain rate and temperature history dependence. A unique and comprehensive set of experiments involving sequences of different strain rates, temperatures, and deformation paths, as well as, constant strain rate, isothermal and experiments characterizing restoration processes, were conducted on OFHC Cu. Microstructural examinations found that recrystallization occurs and has a significant influence on the flow stress. The performance of various models, including state-of-the-art models such as the BCJ (Sandia), MTS (Los Alamos), and McDowell models were correlated and compared to experimental data. A novel hybrid optimization strategy was used to obtain the optimum parameter set possible corresponding to each model form. To account for the observed flow stress softening, an internal state variable representing the "softened" recrystallized state was incorporated into the hardening evolution equations in the BCJ and Mc

  1. Modeling Temperature and Strain Rate History Effects in OFHC Cu

    Science.gov (United States)

    2007-11-02

    Klepaczko and Duffy (1974), OFHC Cu and Al-1100 by Senseny (1977), Cu by Stelly and Dormeval (1977), AISI 316 by Albertini et al. (1985), and on OFHC Cu by...Shukla, et al. 301 (1996) also develops an ANN for function approximation. Through this process, the functional form of experimental data can be...Rate History on the Ambient Tensile Strength of AISI Type 316 Stainless Steel," Nuclear Engineering and Design, Vol. 88, pp. 131-141. Ellwood, S

  2. High Strain Rate Experiments of Energetic Material Binder

    OpenAIRE

    Rangel Mendoza, Roberto; Harr, Michael; Chen, Weinong

    2016-01-01

    Energetic materials, in particular HMX, is widely used in many applications as polymer bonded explosives (PBX) and rocket propellant. However, when damaged, HMX is known to be an unstable substance which renders it a hazardous material and in some cases unreliable. Finding critical mechanical conditions at high rates that render various forms of energetic materials as unreliable would be vital to understand the effects that vibrations and compression forces have on energetic materials. A bett...

  3. High- and low-strain rate compression properties of several energetic material composites as a function of strain rate and temperature

    Energy Technology Data Exchange (ETDEWEB)

    Gray, G.T. III; Idar, D.J.; Blumenthal, W.R.; Cady, C.M.; Peterson, P.D.

    1998-12-31

    High- and low-strain rate compression data were obtained on several different energetic composites: PBX 9501, X0242-92-4-4, PBXN-9, as well as the polymeric binder used in PBX 9501 and X0242-92-4-4 composites. The effects of energetic-to-binder ratios, different binder systems, and different energetic formulations were investigated. All the energetic composites exhibit increasing elastic modulus, E, maximum flow stresses, {sigma}{sub m}, and strain-at-maximum stress, {var_epsilon}{sub m}, with increasing strain rate at ambient temperature. PBX 9501 displays marginally higher ultimate flow strength than X0242-92-4-4, and significantly higher ultimate compressive strength than PBXN-9 at quasi-static and dynamic strain rates. The failure mode of PBX 9501 and X0242-92-4-4 under high-rate loading changes from a mixture of ductile binder tearing and transgranular cleavage and cracking of the HMX when tested at 20 C to transgranular brittle HMX cleavage and glassy fracture of the binder at {minus}40 C.

  4. Effect of Different Stocking Densities on Survival Rates of Nile Tilapia Fingerlings Transported in Plastic Bags.

    Directory of Open Access Journals (Sweden)

    Adam Ibrahim AM

    2015-10-01

    Full Text Available Fish farmers in Sudan obtain their seed stocks mainly not from their farms and as such rely heavily on good packing conditions covering sometimes 8–12 hours transportation time to maximize fish survival and quality the study here required main objective to identified the optimum loading for the success during transporting. closed oxygenated plastic bag which was carried three densities for each one with tow replicate for every treatment for the lower loading is 75 fingerlings /l the medium is, 100 fingerlings and last density is the larger one 140 fingerlings the duration factors was 10 hours, 11 hours and 18 hours. The fingerlings was sex reversed, their size is (5g ± 0.5. The collecting data analyze used SPSS computer software version- 16.0. Analysis result shown the factor of density in the tow treatments (75 fingerlings + 100 fingerlings was the best according to the survivor rate depending to type of the periods parameter. 10 hour=94% and 11 hours = 92% and here was N.S otherwise the comparative between those and the density 140 was high significant. Variation between loading and durations is NS at P<0.05, so the conclusions is found the optimum loading during transporting period was 100/l/18 (hundred fish per litter in 18 hours period according to analysis details.

  5. Phyllosphere yeasts rapidly break down biodegradable plastics.

    Science.gov (United States)

    Kitamoto, Hiroko K; Shinozaki, Yukiko; Cao, Xiao-Hong; Morita, Tomotake; Konishi, Masaaki; Tago, Kanako; Kajiwara, Hideyuki; Koitabashi, Motoo; Yoshida, Shigenobu; Watanabe, Takashi; Sameshima-Yamashita, Yuka; Nakajima-Kambe, Toshiaki; Tsushima, Seiya

    2011-11-29

    The use of biodegradable plastics can reduce the accumulation of environmentally persistent plastic wastes. The rate of degradation of biodegradable plastics depends on environmental conditions and is highly variable. Techniques for achieving more consistent degradation are needed. However, only a few microorganisms involved in the degradation process have been isolated so far from the environment. Here, we show that Pseudozyma spp. yeasts, which are common in the phyllosphere and are easily isolated from plant surfaces, displayed strong degradation activity on films made from poly-butylene succinate or poly-butylene succinate-co-adipate. Strains of P. antarctica isolated from leaves and husks of paddy rice displayed strong degradation activity on these films at 30°C. The type strain, P. antarctica JCM 10317, and Pseudozyma spp. strains from phyllosphere secreted a biodegradable plastic-degrading enzyme with a molecular mass of about 22 kDa. Reliable source of biodegradable plastic-degrading microorganisms are now in our hands.

  6. Dose rate effects in the radiation damage of the plastic scintillators of the CMS Hadron Endcap Calorimeter

    CERN Document Server

    Khachatryan, V.

    2016-01-01

    We present measurements of the reduction of light output by plastic scintillators irradiated in the CMS detector during the 8 TeV run of the Large Hadron Collider and show that they indicate a strong dose rate effect. The damage for a given dose is larger for lower dose rate exposures. The results agree with previous measurements of dose rate effects, but are stronger due to the very low dose rates probed. We show that the scaling with dose rate is consistent with that expected from diffusion effects.

  7. High-Strain Rate Testing of Gun Propellants

    Science.gov (United States)

    1988-12-01

    formulations under high loading rates have been studied previously (see Fong (1985); et al. (1981); Schubert and Schmitt (1973); Greidanus (1976...the transmission of a wave was described by Davies and Hunter (1963) and by Hoge (1970). Impedance is defined as Z = A(pE)h, where A is the area, p is...A = ma, a2u ac a 2U m = p A dx, a = . Assembling these, - p -= at 2 ax at 2 For isotropic elastic materials, a = Ee, where e = au/ax. The partial

  8. Strain rate dependence of impact properties of sintered 316L stainless steel

    Science.gov (United States)

    Lee, Woei-Shyan; Lin, Chi-Feng; Liu, Tsung-Ju

    2006-12-01

    This paper uses a material testing system (MTS) and a compressive split-Hopkinson bar to investigate the impact behaviour of sintered 316L stainless steel at strain rates ranging from 10 -3 s -1 to 7.5 × 10 3 s -1. It is found that the true stress, the rate of work hardening and the strain rate sensitivity vary significantly as the strain rate increases. The flow behaviour of the sintered 316L stainless steel can be accurately predicted using a constitutive law based on Gurson's yield criterion and the flow rule proposed by Khan, Huang and Liang (KHL). Microstructural observations reveal that the degree of localized grain deformation increases, but the pore density and the grain size decrease, with increasing strain rate. Adiabatic shear bands associated with cracking are developed at strain rates higher than 5.6 × 10 3 s -1. The fracture surfaces exhibit ductile dimples. The depth and density of these dimples decrease with increasing strain rate.

  9. Strain rate dependence of impact properties of sintered 316L stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Lee, W.-S. [Department of Mechanical Engineering, National Cheng Kung University, Tainan 701, Taiwan (China)]. E-mail: wslee@mail.ncku.edu.tw; Lin, C.-F. [National Center for High-Performance Computing, Hsin-Shi Tainan County 744, Taiwan (China); Liu, T.-J. [Department of Mechanical Engineering, National Cheng Kung University, Tainan 701, Taiwan (China)

    2006-12-15

    This paper uses a material testing system (MTS) and a compressive split-Hopkinson bar to investigate the impact behaviour of sintered 316L stainless steel at strain rates ranging from 10{sup -3} s{sup -1} to 7.5 x 10{sup 3} s{sup -1}. It is found that the true stress, the rate of work hardening and the strain rate sensitivity vary significantly as the strain rate increases. The flow behaviour of the sintered 316L stainless steel can be accurately predicted using a constitutive law based on Gurson's yield criterion and the flow rule proposed by Khan, Huang and Liang (KHL). Microstructural observations reveal that the degree of localized grain deformation increases, but the pore density and the grain size decrease, with increasing strain rate. Adiabatic shear bands associated with cracking are developed at strain rates higher than 5.6 x 10{sup 3} s{sup -1}. The fracture surfaces exhibit ductile dimples. The depth and density of these dimples decrease with increasing strain rate.

  10. Longitudinal Strain and Strain Rate Abnormalities Precede Invasive Diagnosis of Transplant Coronary Artery Vasculopathy in Pediatric Cardiac Transplant Patients.

    Science.gov (United States)

    Zoeller, Bridget B; Miyamoto, Shelley D; Younoszai, Adel K; Landeck, Bruce F

    2016-04-01

    Transplant coronary artery vasculopathy (TCAV) is the primary cause of late graft loss in pediatric heart transplant recipients. TCAV is diagnosed using angiography or intravascular ultrasound; however, noninvasive methods remain elusive. We sought to define patterns of myocardial mechanics in patients with TCAV and to determine whether this can detect TCAV before invasive methods. In this retrospective study, we queried our heart transplant database to identify all recipients with TCAV since 2006 (n = 41). Echoes were reviewed from the last normal catheterization and at TCAV diagnosis, and from time-matched transplant controls (n = 33) without TCAV. Peak global circumferential and longitudinal strain and systolic and diastolic strain rate (SSR and DSR) of the left ventricle were derived using velocity vector imaging. T tests were used to compare both groups longitudinally and between groups at both time points. Longitudinal strain, SSR, and DSR were diminished in the TCAV group compared to the transplant control group at both time points. No differences were found across time points in either group. Retrospective modeling using a longitudinal strain cutoff of 15 % on echoes 2 years prior to TCAV diagnosis predicted development or exclusion of TCAV with sensitivity of 53 %, specificity of 89 % with an area under the curve of 0.8. Decreases in longitudinal strain measurements demonstrate that alterations in myocardial mechanics occur in patients with TCAV at least 2 years prior to invasive diagnosis. These early changes may be due to microvascular disease. This modality could aid in earlier treatment and intervention for this challenging problem .

  11. HIGH STRAIN RATE BEHAVIOUR OF AN AZ31 + 0.5 Ca MAGNESIUM ALLOY

    Directory of Open Access Journals (Sweden)

    Josef Pešička

    2012-01-01

    Full Text Available The paper reports behaviour of magnesium alloy AZ31 (nominal composition 3 % Al - 1 % Zn – balance Mg with an addition of 0.5 wt. % Ca at high strain rates. Samples were prepared by the squeeze cast technology. Dynamic compression Hopkinson tests were performed at room temperature with impact velocities ranging from 11.2 to 21.9 m.s-1. A rapid increase of the flow stress and the strain rate sensitivity was observed at high strain rates. Transmission electron microscopy showed extremely high dislocation density and mechanical twins of two types. Adiabatic shear banding is discussed as the reason for the observed behaviour at high strain rates.

  12. Prediction of flow stress of 7017 aluminium alloy under high strain rate compression at elevated temperatures

    National Research Council Canada - National Science Library

    Bobbili, Ravindranadh; Ramakrishna, B; Madhu, V; Gogia, A.K

    2015-01-01

    An artificial neural network (ANN) constitutive model and Johnson–Cook (J–C) model were developed for 7017 aluminium alloy based on high strain rate data generated from split Hopkinson pressure bar (SHPB...

  13. Physical mechanisms underlying the strain-rate-dependent mechanical behavior of kangaroo shoulder cartilage

    Science.gov (United States)

    Thibbotuwawa, Namal; Oloyede, Adekunle; Li, Tong; Singh, Sanjleena; Senadeera, Wijitha; Gu, YuanTong

    2015-09-01

    Due to anatomical and biomechanical similarities to human shoulder, kangaroo was chosen as a model to study shoulder cartilage. Comprehensive enzymatic degradation and indentation tests were applied on kangaroo shoulder cartilage to study mechanisms underlying its strain-rate-dependent mechanical behavior. We report that superficial collagen plays a more significant role than proteoglycans in facilitating strain-rate-dependent behavior of the kangaroo shoulder cartilage. By comparing the mechanical properties of degraded and normal cartilages, it was noted that proteoglycan and collagen degradation significantly compromised strain-rate-dependent mechanical behavior of the cartilage. Superficial collagen contributed equally to the tissue behavior at all strain-rates. This is different to the studies reported on knee cartilage and confirms the importance of superficial collagen on shoulder cartilage mechanical behavior. A porohyperelastic numerical model also indicated that collagen disruption would lead to faster damage of the shoulder cartilage than when proteoglycans are depleted.

  14. Measurement of mean rotation and strain-rate tensors by using stereoscopic PIV

    DEFF Research Database (Denmark)

    Özcan, Oktay; Meyer, Knud Erik; Larsen, Poul Scheel

    2005-01-01

    A technique is described for measuring the mean velocity gradient (rate-of-displacement) tensor by using a conventional stereoscopic particle image velocimetry (SPIV) system. Planar measurement of the mean vorticity vector, rate-of-rotation and rate-of-strain tensors and the production of turbulent...

  15. Strain rate sensitivity index's theoretical formulae expressed by experimental parameters and its measurement

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    A group of formulae for measuring strain rate sensitivity index is established under the conditions of constant strain rate, constant velocity and constant load. And measuring methods are given corresponding to each kind of experimental curves. Furthermore the experimental results are measured and compared on Zn-wt5%Al alloy at room temperature (18 ℃), which shows that this kind of alloy is structural sensitive even at room temperature.

  16. The Effect Analysis of Strain Rate on Power Transmission Tower-Line System under Seismic Excitation

    OpenAIRE

    Li Tian; Wenming Wang; Hui Qian

    2014-01-01

    The effect analysis of strain rate on power transmission tower-line system under seismic excitation is studied in this paper. A three-dimensional finite element model of a transmission tower-line system is created based on a real project. Using theoretical analysis and numerical simulation, incremental dynamic analysis of the power transmission tower-line system is conducted to investigate the effect of strain rate on the nonlinear responses of the transmission tower and line. The results sho...

  17. The effect analysis of strain rate on power transmission tower-line system under seismic excitation.

    Science.gov (United States)

    Tian, Li; Wang, Wenming; Qian, Hui

    2014-01-01

    The effect analysis of strain rate on power transmission tower-line system under seismic excitation is studied in this paper. A three-dimensional finite element model of a transmission tower-line system is created based on a real project. Using theoretical analysis and numerical simulation, incremental dynamic analysis of the power transmission tower-line system is conducted to investigate the effect of strain rate on the nonlinear responses of the transmission tower and line. The results show that the effect of strain rate on the transmission tower generally decreases the maximum top displacements, but it would increase the maximum base shear forces, and thus it is necessary to consider the effect of strain rate on the seismic analysis of the transmission tower. The effect of strain rate could be ignored for the seismic analysis of the conductors and ground lines, but the responses of the ground lines considering strain rate effect are larger than those of the conductors. The results could provide a reference for the seismic design of the transmission tower-line system.

  18. Strain Rate Dependent Ductile-to-Brittle Transition of Graphite Platelet Reinforced Vinyl Ester Nanocomposites

    Directory of Open Access Journals (Sweden)

    Brahmananda Pramanik

    2014-01-01

    Full Text Available In previous research, the fractal dimensions of fractured surfaces of vinyl ester based nanocomposites were estimated applying classical method on 3D digital microscopic images. The fracture energy and fracture toughness were obtained from fractal dimensions. A noteworthy observation, the strain rate dependent ductile-to-brittle transition of vinyl ester based nanocomposites, is reinvestigated in the current study. The candidate materials of xGnP (exfoliated graphite nanoplatelets reinforced and with additional CTBN (Carboxyl Terminated Butadiene Nitrile toughened vinyl ester based nanocomposites that are subjected to both quasi-static and high strain rate indirect tensile load using the traditional Brazilian test method. High-strain rate indirect tensile testing is performed with a modified Split-Hopkinson Pressure Bar (SHPB. Pristine vinyl ester shows ductile deformation under quasi-static loading and brittle failure when subjected to high-strain rate loading. This observation reconfirms the previous research findings on strain rate dependent ductile-to-brittle transition of this material system. Investigation of both quasi-static and dynamic indirect tensile test responses show the strain rate effect on the tensile strength and energy absorbing capacity of the candidate materials. Contribution of nanoreinforcement to the tensile properties is reported in this paper.

  19. Mechanical model for yield strength of nanocrystalline materials under high strain rate loading

    Institute of Scientific and Technical Information of China (English)

    朱荣涛; 周剑秋; 马璐; 张振忠

    2008-01-01

    To understand the high strain rate deformation mechanism and determine the grain size,strain rate and porosity dependent yield strength of nanocrystalline materials,a new mechanical model based on the deformation mechanism of nanocrystalline materials under high strain rate loading was developed.As a first step of the research,the yield behavior of the nanocrystalline materials under high strain rate loading was mainly concerned in the model and uniform deformation was assumed for simplification.Nanocrystalline materials were treated as composites consisting of grain interior phase and grain boundary phase,and grain interior and grain boundary deformation mechanisms under high strain rate loading were analyzed,then Voigt model was applied to coupling grain boundary constitutive relation with mechanical model for grain interior phase to describe the overall yield mechanical behavior of nanocrystalline materials.The predictions by the developed model on the yield strength of nanocrysatlline materials at high strain rates show good agreements with various experimental data.Further discussion was presented for calculation results and relative experimental observations.

  20. Nucleation mechanisms of dynamic recrystallization in Inconel 625 superalloy deformed with different strain rates

    Institute of Scientific and Technical Information of China (English)

    2012-01-01

    The effects of strain rates on the hot working characteristics and nucleation mechanisms of dynamic recrystallization (DRX) were studied by optical microscopy and electron backscatter diffraction (EBSD) technique. Hot compression tests were conducted using a Gleeble-1500 simulator at a true strain of 0.7 in the temperature range of 1000 to 1150 °C and strain rate range of 0.01 to 10.00 s-1. It is found that the size and volume fraction of the DRX grains in hot-deformed Inconel 625 superalloy firstly decreas...

  1. MEASUREMENTS OF HIGH STRAIN RATE PROPERTIES OF MATERIALS USING AN EXPLODING WIRE TECHNIQUE

    OpenAIRE

    Parry, D; Stewardson, H.; Ahmad, S.

    1988-01-01

    An exploding wire method is used to produce high-pressure blast-wave loading of thick polymer cylinders. The measured outer-surface hoop-strain profiles, at strain rates of about 103 s-1, agree best with prediction for values of Young's modulus which are much higher than those measured under quasistatic conditions (strain rates of about 10-3 s-1). Low density polyethylene shows a six-fold increase in modulus, high density polyethylene more than 100%, nylon 66 about 75%, and nylatron a 25% inc...

  2. A Constitutive Model for Superelastic Shape Memory Alloys Considering the Influence of Strain Rate

    Directory of Open Access Journals (Sweden)

    Hui Qian

    2013-01-01

    Full Text Available Shape memory alloys (SMAs are a relatively new class of functional materials, exhibiting special thermomechanical behaviors, such as shape memory effect and superelasticity, which enable their applications in seismic engineering as energy dissipation devices. This paper investigates the properties of superelastic NiTi shape memory alloys, emphasizing the influence of strain rate on superelastic behavior under various strain amplitudes by cyclic tensile tests. A novel constitutive equation based on Graesser and Cozzarelli’s model is proposed to describe the strain-rate-dependent hysteretic behavior of superelastic SMAs at different strain levels. A stress variable including the influence of strain rate is introduced into Graesser and Cozzarelli’s model. To verify the effectiveness of the proposed constitutive equation, experiments on superelastic NiTi wires with different strain rates and strain levels are conducted. Numerical simulation results based on the proposed constitutive equation and experimental results are in good agreement. The findings in this paper will assist the future design of superelastic SMA-based energy dissipation devices for seismic protection of structures.

  3. Dynamic tensile behavior of AZ31B magnesium alloy at ultra-high strain rates

    Directory of Open Access Journals (Sweden)

    Geng Changjian

    2015-04-01

    Full Text Available The samples having {0001} parallel to extruding direction (ED present a typical true stress–true strain curve with concave-down shape under tension at low strain rate. Ultra-rapid tensile tests were conducted at room temperature on a textured AZ31B magnesium alloy. The dynamic tensile behavior was investigated. The results show that at ultra-high strain rates of 1.93 × 102 s−1 and 1.70 × 103 s−1, the alloy behaves with a linear stress–strain response in most strain range and exhibits a brittle fracture. In this case, {10-12}  extension twinning is basic deformation mode. The brittleness is due to the macroscopic viscosity at ultra-high strain rate, for which the external critical shear stress rapidly gets high to result in a cleavage fracture before large amounts of dislocations are activated. Because {10-12} tension twinning, {10-11} compressive twinning, basal slip, prismatic slip and pyramidal slip have different critical shear stresses (CRSS, their contributions to the degree of deformation are very differential. In addition, Schmid factor plays an important role in the activity of various deformation modes and it is the key factor for the samples with different strain rates exhibit various mechanical behavior under dynamic tensile loading.

  4. Machined and plastic copings in three-element prostheses with different types of implantabutment joints: a strain gauge comparative analysis

    Directory of Open Access Journals (Sweden)

    Renato Sussumu Nishioka

    2010-06-01

    Full Text Available OBJECTIVE: Using strain gauge (SG analysis, the aim of this in vitro study was quantify the strain development during the fixation of three-unit screw implant-supported fixed partial dentures, varying the types of implant-abutment joints and the type of prosthetic coping. The hypotheses were that the type of hexagonal connection would generate different microstrains and the type of copings would produce similar microstrains after prosthetic screws had been tightened onto microunit abutments. MATERIALS AND METHODS: Three dental implants with external (EH and internal (IH hexagonal configurations were inserted into two polyurethane blocks. Microunit abutments were screwed onto their respective implant groups, applying a torque of 20 Ncm. Machined Co-Cr copings (M and plastic prosthetic copings (P were screwed onto the abutments, which received standard wax patterns. The wax patterns were cast in Co-Cr alloy (n=5, forming four groups: G1 EH/M; G2 EH/P; G3 IH/M and G4 IH/P. Four SGs were bonded onto the surface of the block tangentially to the implants, SG 1 mesially to implant 1, SG 2 and SG 3 mesially and distally to implant 2, respectively, and SG 4 distally to implant 3. The superstructure's occlusal screws were tightened onto microunit abutments with 10 Ncm torque using a manual torque driver. The magnitude of microstrain on each SG was recorded in units of microstrain (µε. The data were analyzed statistically by ANOVA and Tukey's test (p0.05. The hypotheses were partially accepted. CONCLUSIONS: It was concluded that the type of hexagonal connection and coping presented similar mechanical behavior under tightening conditions.

  5. Possibility of Prediction of Properties of High-Toughness Materials by Complex Analysis of the Size of Zones of Plastic Strain and Other Parameters of Steel 09G2S

    Science.gov (United States)

    Simonov, M. Yu.; Shaimanov, G. S.; Simonov, Yu. N.; Khanov, A. M.

    2016-05-01

    Relations between the parameters of dynamic crack resistance, impact toughness, sizes of zones of plastic strain in the start region, hardness of the unstrained material, strength characteristics, and tempering temperature of steel 09G2S are determined. The linear regression equations are used to construct mathematical and graphical models for predicting the level of properties in quenched and tempered steel 09G2S. The method is used to predict the properties of a tubular billet from steel 09G2S with composition somewhat different from the rated one after quenching and high tempering at 570°C.

  6. Low plastic ingestion rate in Atlantic cod (Gadus morhua) from Newfoundland destined for human consumption collected through citizen science methods.

    Science.gov (United States)

    Liboiron, Max; Liboiron, France; Wells, Emily; Richárd, Natalie; Zahara, Alexander; Mather, Charles; Bradshaw, Hillary; Murichi, Judyannet

    2016-12-15

    Marine microplastics are a contaminant of concern because their small size allows ingestion by a wide range of marine life. Using citizen science during the Newfoundland recreational cod fishery, we sampled 205 Atlantic cod (Gadus morhua) destined for human consumption and found that 5 had eaten plastic, an ingestion prevalence rate of 2.4%. This ingestion rate for Atlantic cod is the second lowest recorded rate in the reviewed published literature (the lowest is 1.4%), and the lowest for any fish in the North Atlantic. This is the first report for plastic ingestion in fish in Newfoundland, Canada, a province dependent on fish for sustenance and livelihoods. Copyright © 2016 Elsevier Ltd. All rights reserved.

  7. Constitutive model depending upon temperature and strain rate of carbon constructional quality steels

    Institute of Scientific and Technical Information of China (English)

    杨柳; 罗迎社

    2008-01-01

    The basic factors relating to the rheological stress in the constitutive equations were introduced.Carbon constructional quality steels were regarded as a kind of elastic-viscoplastic materials under high temperature and the elastic-viscoplastic constitutive models were summarized.A series of tension experiments under the same temperature and different strain rates,and the same strain rate and different temperatures were done on 20 steel,35 steel and 45 steel.52 groups of rheological stress-strain curves were obtained.The experimental results were analyzed theoretically.The rheological stress constitutive models of carbon steels were built combining the strong points of the Perzyna model and Johnson-Cook model.Comparing the calculation results conducted from the model with the experiment results,the results proves that the model can reflect the temperature effect and strain rate effect of carbon constructional quality steels better.

  8. Influence of the temperature on the tension behaviour of EUROFER97 alloy at high strain rate

    Directory of Open Access Journals (Sweden)

    Cadoni Ezio

    2015-01-01

    Full Text Available This paper presents an experimental investigation on the influence of the temperature on the reduced activation steel Eurofer97 under uniaxial tensile loads at high strain rate. Round undamaged specimens of this material having gauge length 5 mm, diameter 3 mm, were tested in universal machine to obtain its stress-strain relation under quasi-static condition (0.001s−1, and in modified Hopkinson bar to study its mechanical behaviour at high strain rates (300 s−1, 1000 s−1 respectively. The tests at high strain rate were carried out at 450 °C and at nitrogen temperature. Finally, the parameters of the Zerilli-Armstrong constitutive material relationship were obtained.

  9. Refinement of the wedge bar technique for compression tests at intermediate strain rates

    Directory of Open Access Journals (Sweden)

    Stander M.

    2012-08-01

    Full Text Available A refined development of the wedge-bar technique [1] for compression tests at intermediate strain rates is presented. The concept uses a wedge mechanism to compress small cylindrical specimens at strain rates in the order of 10s−1 to strains of up to 0.3. Co-linear elastic impact principles are used to accelerate the actuation mechanism from rest to test speed in under 300μs while maintaining near uniform strain rates for up to 30 ms, i.e. the transient phase of the test is less than 1% of the total test duration. In particular, a new load frame, load cell and sliding anvil designs are presented and shown to significantly reduce the noise generated during testing. Typical dynamic test results for a selection of metals and polymers are reported and compared with quasistatic and split Hopkinson pressure bar results.

  10. LS-DYNA Implementation of Polymer Matrix Composite Model Under High Strain Rate Impact

    Science.gov (United States)

    Zheng, Xia-Hua; Goldberg, Robert K.; Binienda, Wieslaw K.; Roberts, Gary D.

    2003-01-01

    A recently developed constitutive model is implemented into LS-DYNA as a user defined material model (UMAT) to characterize the nonlinear strain rate dependent behavior of polymers. By utilizing this model within a micromechanics technique based on a laminate analogy, an algorithm to analyze the strain rate dependent, nonlinear deformation of a fiber reinforced polymer matrix composite is then developed as a UMAT to simulate the response of these composites under high strain rate impact. The models are designed for shell elements in order to ensure computational efficiency. Experimental and numerical stress-strain curves are compared for two representative polymers and a representative polymer matrix composite, with the analytical model predicting the experimental response reasonably well.

  11. The direct effects of strain on burning rates of composite solid propellants

    Science.gov (United States)

    Langhenry, M. T.

    1984-01-01

    A mathematical model is developed to predict burn rate augmentation due to strain in a composite solid propellant. The model assumes the effect is due to the ability of the flame to penetrate the small fissures and voids that form when a propellant is strained. The number and size of these fissures is obtained by applying a flaw propagation analysis to randomly distributed flaws that form when the binder-oxidizer particle bonds break under stress. A flame height is calculated with Summerfield's burn rate equation and is used to compute the burn rate augmentation based upon the additional burn area created when the flame penetrates the fissures. Comparisons are made with data obtained from published sources. The existence of threshold pressure and strains, above which augmentation occurs, is verified although the model predicts a lower threshold pressure and higher threshold strain than expected. Further results and applications of the model are discussed.

  12. Maximum Likelihood based comparison of the specific growth rates for P. aeruginosa and four mutator strains

    DEFF Research Database (Denmark)

    Philipsen, Kirsten Riber; Christiansen, Lasse Engbo; Mandsberg, Lotte Frigaard

    2008-01-01

    that best describes data is a model taking into account the full covariance structure. An inference study is made in order to determine whether the growth rate of the five bacteria strains is the same. After applying a likelihood-ratio test to models with a full covariance structure, it is concluded...... that the specific growth rate is the same for all bacteria strains. This study highlights the importance of carrying out an explorative examination of residuals in order to make a correct parametrization of a model including the covariance structure. The ML method is shown to be a strong tool as it enables......The specific growth rate for P. aeruginosa and four mutator strains mutT, mutY, mutM and mutY–mutM is estimated by a suggested Maximum Likelihood, ML, method which takes the autocorrelation of the observation into account. For each bacteria strain, six wells of optical density, OD, measurements...

  13. Flow Curve Determination at Large Plastic Strain Levels: Limitations of the Membrane Theory in the Analysis of the Hydraulic Bulge Test

    Science.gov (United States)

    Lemoine, X.; Iancu, A.; Ferron, G.

    2011-05-01

    Nowadays, an accurate determination of the true stress-strain curve is a key-element for all finite element (FE) forming predictions. Since the introduction of Advanced High Strength Steels (AHSS) for the automotive market, the standard uniaxial tension test suffers the drawback of relatively low uniform elongations. The extrapolation of the uniaxial stress-strain curve up to large strains is not without consequence in forming predictions—especially formability and springback. One of the means to solve this problem is to use experimental tests where large plastic strain levels can be reached. The hydraulic bulge test is one of these tests. The effective plastic strain levels reached in the bulge test are of about 0.7. From an experimental standpoint, the biaxial flow stress is estimated using measurement of fluid pressure, and calculation of thickness and curvature at the pole, via appropriate measurements and assumptions. The biaxial stress at the pole is determined using the membrane equilibrium equation. The analysis proposed in this paper consists of performing "virtual experiments" where the results obtained by means of FE calculations are used as input data for determining the biaxial stress-strain law in agreement with the experimental procedure. In this way, a critical discussion of the experimental procedure can be made, by comparing the "experimental" stress-strain curve (Membrane theory curve) with the "reference" one introduced in the simulations. In particular, the influences of the "(die diameter)/thickness" ratio and of the plastic anisotropy are studied, and limitations of the hydraulic bulge test analysis are discussed.

  14. Dynamic tensile fracture of mortar at ultra-high strain-rates

    Energy Technology Data Exchange (ETDEWEB)

    Erzar, B., E-mail: benjamin.erzar@cea.fr; Buzaud, E.; Chanal, P.-Y. [CEA, DAM, GRAMAT, F-46500 Gramat (France)

    2013-12-28

    During the lifetime of a structure, concrete and mortar may be exposed to highly dynamic loadings, such as impact or explosion. The dynamic fracture at high loading rates needs to be well understood to allow an accurate modeling of this kind of event. In this work, a pulsed-power generator has been employed to conduct spalling tests on mortar samples at strain-rates ranging from 2 × 10{sup 4} to 4 × 10{sup 4} s{sup −1}. The ramp loading allowed identifying the strain-rate anytime during the test. A power law has been proposed to fit properly the rate-sensitivity of tensile strength of this cementitious material over a wide range of strain-rate. Moreover, a specimen has been recovered damaged but unbroken. Micro-computed tomography has been employed to study the characteristics of the damage pattern provoked by the dynamic tensile loading.

  15. Prognostic value of strain and strain rate in the prediction of postoperative atrial fibrillation in patients undergoing coronary artery bypass grafting: a systematic literature review

    Directory of Open Access Journals (Sweden)

    Leila Bigdelu

    2016-03-01

    Full Text Available Introduction: Atrial fibrillation (AF is a common dysrhythmia postoperatively after coronary artery bypass grafting (CABG. Myocardial strain and strain-rate imaging is used for the assessment of postoperative atrial fibrillation (POAF as a new echocardiographic method. Methods: PubMed and Scopus were searched thoroughly using the following search terms: (strain and strain rate AND (atrial fibrillation OR AF on March 2015 to find English articles in which the strain and strain-rate echocardiographic imaging had been used for the evaluation of AF in patients undergone CABG. Full text of the relevant papers was fully reviewed for data extraction.Result: Of overall 6 articles found in PubMed, 10 records found in Scopus and 4 articles found through reference list search, only 6 papers fully met the inclusion criteria for further assessment and data extraction. The results of strain and strain-rate assessment showed that in total of 542 patients undergoing CABG, POAF occurred in 106 patients. Studies showed that the reduction of left atrial (LA strain rate is correlated with AF. Consistently, the results of present review showed that LA strain and strain-rate in patients who developed AF postoperatively after CABG are significantly reduced, suggesting that strain and strain-rate could be a predictor of POAF.Conclusion: Based on the obtained results, strain and strain-rate is a suitable and accurate echocardiographic technique in the assessment of left atrial function , and it might be helpful to detect the patients who are at high risk of POAF.

  16. Study of mechanical properties, microstructures and corrosion behavior of al 7075 t651 alloy with varying strain rate

    Science.gov (United States)

    Mukherjee, A.; Ghosh, M.; Mondal, K.; Venkitanarayanan, P.; Moon, A. P.; Varshney, A.

    2015-02-01

    Compression test of Al 7075 T651 was carried out at high strain rates (1138 - 2534 s-1) using Split Hopkinson Pressure Bar and at slow strain rate (10-4s-1) in 100KN Universal Testing machine to understand the improvement in mechanical properties and associated changes in microstructures. Cylindrical specimens of 6 mm height and 6 mm diameter were compressed dynamically. The influence of strain rates on mechanical properties, microstructure evolution and corrosion behavior after immersion test in 3.5% NaCl solution was also investigated. Strain rate, withdrawal stress and yield stress were observed to increase with impact velocity in high strain rate tests, while in slow strain rate tests, n value was observed to increase with increasing total strain. Microstructural observations revealed that after high strain rate test, grains of Al matrix were elongated. It was observed that corrosion resistance decreased with increase in impact velocity.

  17. Temperature and strain rate effects in high strength high conductivity copper alloys tested in air

    Energy Technology Data Exchange (ETDEWEB)

    Edwards, D.J. [Pacific Northwest National Lab., Richland, WA (United States)

    1998-03-01

    The tensile properties of the three candidate alloys GlidCop{trademark} Al25, CuCrZr, and CuNiBe are known to be sensitive to the testing conditions such as strain rate and test temperature. This study was conducted on GlidCop Al25 (2 conditions) and Hycon 3HP (3 conditions) to ascertain the effect of test temperature and strain rate when tested in open air. The results show that the yield strength and elongation of the GlidCop Al25 alloys exhibit a strain rate dependence that increases with temperature. Both the GlidCop and the Hycon 3 HP exhibited an increase in strength as the strain rate increased, but the GlidCop alloys proved to be the most strain rate sensitive. The GlidCop failed in a ductile manner irrespective of the test conditions, however, their strength and uniform elongation decreased with increasing test temperature and the uniform elongation also decreased dramatically at the lower strain rates. The Hycon 3 HP alloys proved to be extremely sensitive to test temperature, rapidly losing their strength and ductility when the temperature increased above 250 C. As the test temperature increased and the strain rate decreased the fracture mode shifted from a ductile transgranular failure to a ductile intergranular failure with very localized ductility. This latter observation is based on the presence of dimples on the grain facets, indicating that some ductile deformation occurred near the grain boundaries. The material failed without any reduction in area at 450 C and 3.9 {times} 10{sup {minus}4} s{sup {minus}1}, and in several cases failed prematurely.

  18. Strain Rate Dependent Behavior of Glass/Nano Clay Filled Epoxy Resin Composite

    Directory of Open Access Journals (Sweden)

    R. Velmurugan

    2014-05-01

    Full Text Available It is believed that addition of small amount of nanoclays in the neat epoxy and fiber reinforced epoxy composite system can improve the mechanical properties. The mechanical properties of most of polymer matrix composites are sensitive to testing rate. However, most of the researches were concentrated on the behavior of the polymer matrix composites at high strain rates. The present research work is to investigate the role of clay on neat epoxy and glass–fiber reinforced epoxy composites, at low strain rates. The clay in terms of 1.5 wt%, 3 wt%, and 5 wt% are dispersed in the epoxy resin using mechanical stirring followed by sonication process. The corresponding glass/epoxy nanocomposites are prepared by impregnating the clay epoxy mixture by hand lay-up process. Characterization of the nanoclay is done by X-ray diffraction and Scanning Electron Microscopy. Tensile stress-strain curves are obtained at strain rates of 10-4 s-1, 10-3 s-1, 10-2 s-1, and 10-1 s-1 by a hydraulic machine reporting that, even at low strain rates, the longitudinal strength and stiffness increase as strain rate increases for all clay loadings. It is observed that the tensile modulus increases as the clay loading increases for both epoxy and glass/epoxy nanocomposites. It is also noticed that the longitudinal tensile strength decreases as the clay loading increases. The failed specimens show marked changes in the fracture surface with increased strain rate. Scanning electron microscopy is used to study the fiber/matrix/clay adhesion in fracture surfaces.

  19. Strain Rate Dependent Behavior of Glass/Nano Clay Filled Epoxy Resin Composite

    Directory of Open Access Journals (Sweden)

    R. Velmurugan

    2014-05-01

    Full Text Available It is believed that addition of small amount of nanoclays in the neat epoxy and fiber reinforced epoxy composite system can improve the mechanical properties. The mechanical properties of most of polymer matrix composites are sensitive to testing rate. However, most of the researches were concentrated on the behavior of the polymermatrix composites at high strain rates. The present research work is to investigate the role of clay on neat epoxy and glass–fiber reinforced epoxy composites, at low strain rates. The clay in terms of 1.5 wt%, 3 wt%, and 5 wt% are dispersed in the epoxy resin using mechanical stirring followed by sonication process. The corresponding glass/epoxy nanocomposites are prepared by impregnating the clay epoxy mixture by hand lay-up process. Characterization of the nanoclay is done by X-ray diffraction and Scanning Electron Microscopy. Tensile stress-strain curves are obtained at strain rates of 10-4 s-1, 10-3 s-1, 10-2 s-1, and 10-1 s-1 by a hydraulic  machine reporting that, even at low strain rates, the longitudinal strength and stiffness increase as strain rate increases for all clay loadings. It is observed that the tensile modulus increases as the clay loading increases for both epoxy and glass/epoxy nanocomposites. It is also noticed that the longitudinal tensile strength decreases as the clay loading increases. The failed specimens show marked changes in the fracture surface with increased strain rate. Scanning electron microscopy is used to study the fiber/matrix/clay adhesion in fracture surfaces.Defence Science Journal, Vol. 64, No. 3, May 2014, pp. 295-302, DOI:http://dx.doi.org/10.14429/dsj.64.7331

  20. Detection of Left Ventricular Regional Function in Asymptomatic Children with beta-Thalassemia Major by Longitudinal Strain and Strain Rate Imaging

    Directory of Open Access Journals (Sweden)

    Ali Bay

    2013-09-01

    Full Text Available Objective: Cardiac failure due to iron overload remains the most common cause of death in patients with beta-thalassemia major. This study aimed to evaluate myocardial function in children with beta-thalassemia major using standard echocardiography technique and strain rate imaging. Materials and Methods: Conventional echocardiographic analysis, tissue velocity imaging, and strain/strain rate imaging of the left ventricle were evaluated in 48 children with beta thalassemia major (19 girls, 29 boys; 8.39±4.05 years and 22 healthy children (11 girls, 11 boys; 8±3.72 years. Results: Conventional echocardiographic examinations revealed that beta-thalassemia patients had larger left ventricular end-systolic diameter, end-diastolic and end-systolic volume, left ventricular mass index, and mitral early/late diastolic flow velocity ratio (p<0.05. Strain and strain rate imaging study of the basal lateral wall of the left ventricle was higher in patients than in controls, at p=0.035 and p=0.008, respectively. Conclusion: We found that superior systolic strain and strain rate imaging of the left ventricle indicated the presence of regional systolic function in the left ventricular wall. We suggest that left ventricle volume and mass index parameters might be more sensitive than the other conventional and strain/strain rate imaging parameters during childhood. However, the adulthood strain and strain rate imaging values may be lower than controls, exceeding the critical level of iron overload.

  1. Strain Rate and Temperature Effects on the Formability and Damage of Advanced High-Strength Steels

    Science.gov (United States)

    Winkler, S.; Thompson, A.; Salisbury, C.; Worswick, M.; van Riemsdijk, I.; Mayer, R.

    2008-06-01

    In order to understand the crashworthiness and formability of advance high-strength steels, the effects of strain rate and temperature on the constitutive response of DP 600 and DP 780 steel tubes were investigated and compared with commercial drawing quality (DQ) and high strength low alloy (HSLA) 350 steel tubes. Uniaxial tensile tests were conducted at quasi-static (QS) (0.003 and 0.1 s-1), intermediate (30 and 100 s-1), and high (500, 1000, and 1500 s-1) strain rates using an Instron, instrumented falling weight impact tester and tensile split Hopkinson bar (TSHB) apparatus, respectively. Elevated temperature tests at 150 °C and 300 °C were also conducted at high strain rates. Following testing, metallography and microscopy techniques were used for material and damage characterization. The results obtained show that the steels studied exhibit a positive strain rate sensitivity. Compared to DQ and HSLA 350, the DP steels were found to have less formability at QS rates but enhanced formability at higher strain rates. A decrease in strength and ductility was measured with increasing temperature for the DP steels, indicating a reduction in energy adsorption due to adiabatic heating during a crash event.

  2. A parametric study on the dynamic behavior of porous bronze at various strain rates

    Science.gov (United States)

    Zhang, Yue; Hu, Jianxing; Lei, Jianyin; Wang, Zhihua; Zhao, Longmao

    2016-10-01

    An experimental investigation on the porous bronze at various strain rates is firstly carried out in this study to explore the effects of relative density and strain rate in the mechanical behavior. Furthermore, a multi-parameter constitutive model of describing the rate-dependent behavior for porous bronze is developed. The parameters in the constitutive model are density dependent, and the specific forms of these parameters as functions of relative density are obtained. It can be concluded from the test results and constitutive model that the high relative density leads to increase in yield strength and energy absorption capacity of the materials and the strain rate also has positive effects on the yield strength and energy absorption capacity of porous bronze.

  3. High Strain-Rate and Quasi-Static Ductile Failure Mechanisms in Porous Materials

    Science.gov (United States)

    2007-11-02

    detailed understanding of the interrelated physical mechanisms that can result in ductile material failure in rate-dependent porous crystalline materials subjected...strains and slip-rates, and hydrostatic stresses on failure paths and ligament damage in face centered cubic (f.c.c.) crystalline materials have been

  4. Impact Compression Experiment for EPS Foam under Mid-high Strain Rate%中高应变率下EPS泡沫的冲击压缩实验

    Institute of Scientific and Technical Information of China (English)

    徐沛保; 巫绪涛; 李和平

    2012-01-01

    用SHPB装置对三种密度的发泡聚苯乙烯(Expanded Polystyrene,EPS)材料进行了从300/s至1400/s共五个中高应变率下的冲击压缩实验.实验中采用波分离技术有效延长应力-应变曲线的测量范围,并简要介绍了其原理和具体实施办法.所有应变率下均获得了含有弹性段、平台屈服段和压实段完整三阶段的应力-应变曲线.曲线的重复性较好,应变率基本恒定.实验结果表明,相同密度EPS泡沫应力-应变曲线的屈服平台段长度随应变率的增加而增加,且趋于平缓.在相近应变率下,随EPS泡沫的密度增加,屈服应力增加,而变形及吸能能力减弱.%Impact compression experiment was carried by using Split Hopkinson Pressure Bar (SHPB) for expanded polystyrene (EPS) foams with three different densities and under five different mid-high strain rates ranging from 300/s to 1400/s. In experiment, wave separation technique was adopted to extend the measuring range of stress-strain curve. Principle and implement of this method is introduced briefly in this paper. Integrated three-stage stress-strain curve including elastic region, plastic collapsing region and densification region was all obtained under different strain rates. Curves have better repeatability and strain rate is basically kept constant. Experimental results show that for EPS foam with the same density, the length of plastic collapsing region in a stress-strain curve increases and the curve form flattens along with strain rate increase. Under similar strain rate, the yield stress increases with the increasing of EPS foam density, but the ability of deformation and energy absorption are weakened.

  5. Strain Rate Sensitivity of Epoxy Resin in Tensile and Shear Loading

    Science.gov (United States)

    Gilat, Amos; Goldberg, Robert K.; Roberts, Gary D.

    2005-01-01

    The mechanical response of E-862 and PR-520 resins is investigated in tensile and shear loadings. At both types of loading the resins are tested at strain rates of about 5x10(exp 5), 2, and 450 to 700 /s. In addition, dynamic shear modulus tests are carried out at various frequencies and temperatures, and tensile stress relaxation tests are conducted at room temperature. The results show that the toughened PR-520 resin can carry higher stresses than the untoughened E-862 resin. Strain rate has a significant effect on the response of both resins. In shear both resins show a ductile response with maximum stress that is increasing with strain rate. In tension a ductile response is observed at low strain rate (approx. 5x10(exp 5) /s), and brittle response is observed at the medium and high strain rates (2, and 700 /s). The hydrostatic component of the stress in the tensile tests causes premature failure in the E-862 resin. Localized deformation develops in the PR-520 resin when loaded in shear. An internal state variable constitutive model is proposed for modeling the response of the resins. The model includes a state variable that accounts for the effect of the hydrostatic component of the stress on the deformation.

  6. High Strain-Rate Material Model Validation for Laser Peening Simulation

    Directory of Open Access Journals (Sweden)

    Kristina Langer

    2015-09-01

    Full Text Available Finite element modeling can be a powerful tool for predicting residual stresses induced by laser peening; however the sign and magnitude of the stress predictions depend strongly on how the material model captures the high strain rate response. Although a Johnson-Cook formulation is often employed, its suitability for modeling phenomena at very high strain rates has not been rigorously evaluated. In this paper, we address the effectiveness of the Johnson-Cook model, with parameters developed from lower strain rate material data (∼10^3 s^–1, to capture the higher strain rate response (∼10^5–10^6 s^–1 encountered during the laser peening process. Published Johnson-Cook parameters extracted from split Hopkinson bar testing were used to predict the shock response of aluminum samples during high-impact flyer plate tests. Additional quasi-static and split Hopkinson bar tests were also conducted to study the model response in the lower strain rate regime. The overall objective of the research was to ascertain whether a material model based on conventional test data (quasi-static compression testing and split Hopkinson bar measurements can credibly be used in FE simulations to predict laser peen-induced stresses.

  7. Effect of intense plastic straining on microstructure and mechanical properties of an Al-Mg-Sc alloy

    Energy Technology Data Exchange (ETDEWEB)

    Kaibyshev, R [Belgorod State University, Pobeda 85, Belgorod, 308015 (Russian Federation); Avtokratova, E; Sitdikov, O, E-mail: rustam_kaibyshev@bsu.edu.r [Institute for Metals Superplasticity Problems, Khalturina 39, Ufa, 450001 (Russian Federation)

    2010-07-01

    An Al-5%Mg-0.18%Mn-0.2%Sc-0.08%Zr-0.002%Be was subjected to equal-channel angular extrusion up to true strains of {approx}3 and {approx}8, that resulted in the formation of partially recrystallized and fully recrystallized structure, respectively. It was shown that the alloy with partially recrystallized structure exhibits highest strength and ductility. The material with fully recrystallized structure showed lowest fatigue crack growth rate and highest value of fracture toughness. Reasons of this unusual effect of microstructure on crack propagation resistance under fatigue are discussed.

  8. Effect of intense plastic straining on microstructure and mechanical properties of an Al-Mg-Sc alloy

    Science.gov (United States)

    Kaibyshev, R.; Avtokratova, E.; Sitdikov, O.

    2010-07-01

    An Al-5%Mg-0.18%Mn-0.2%Sc-0.08%Zr-0.002%Be was subjected to equal-channel angular extrusion up to true strains of ~3 and ~8, that resulted in the formation of partially recrystallized and fully recrystallized structure, respectively. It was shown that the alloy with partially recrystallized structure exhibits highest strength and ductility. The material with fully recrystallized structure showed lowest fatigue crack growth rate and highest value of fracture toughness. Reasons of this unusual effect of microstructure on crack propagation resistance under fatigue are discussed.

  9. Adiabatic shear localization evolution for steel based on the Johnson-Cook model and gradient-dependent plasticity

    Institute of Scientific and Technical Information of China (English)

    Xuebin Wang

    2006-01-01

    Gradient-dependent plasticity is introduced into the phenomenological Johnson-Cook model to study the effects of strainhardening, strain rate sensitivity, thermal-softening, and microstructure. The microstructural effect (interactions and interplay among microstructures) due to heterogeneity of texture plays an important role in the process of development or evolution of an adiabatic shear band with a certain thickness depending on the grain diameter. The distributed plastic shear strain and deformation in the shear band are derived and depend on the critical plastic shear strain corresponding to the peak flow shear stress, the coordinate or position, the internal length parameter, and the average plastic shear strain or the flow shear stress. The critical plastic shear strain, the distributed plastic shear strain, and deformation in the shear band are numerically predicted for a kind of steel deformed at a constant shear strain rate.Beyond the peak shear stress, the local plastic shear strain in the shear band is highly nonuniform and the local plastic shear deformation in the band is highly nonlinear. Shear localization is more apparent with the increase of the average plastic shear strain. The calculated distributions of the local plastic shear strain and deformation agree with the previous numerical and experimental results.

  10. Discrete dislocation plasticity analysis of loading rate-dependent static friction

    NARCIS (Netherlands)

    Song, H.; Deshpande, V. S.; van der Giessen, E.

    2016-01-01

    From a microscopic point of view, the frictional force associated with the relative sliding of rough surfaces originates from deformation of the material in contact, by adhesion in the contact interface or both. We know that plastic deformation at the size scale of micrometres is not only dependent

  11. Experimental characterization and modelling of UO2 behavior at high temperatures and high strain rates

    Science.gov (United States)

    Salvo, Maxime; Sercombe, Jérôme; Ménard, Jean-Claude; Julien, Jérôme; Helfer, Thomas; Désoyer, Thierry

    2015-01-01

    This work presents an experimental characterization of uranium dioxide (UO2) in compression under Reactivity Initiated Accident (RIA) conditions. Pellet samples were tested at four temperatures (1100, 1350, 1550 and 1700 °C) and at a strain rate varying over 4 decades (10-4-10-3-10-2-10-1 /s). The experimental results show that the stress-strain curves cannot be fitted with a unique power law as it is the case at smaller strain rates (10-9-10-5 /s). A strain-hardening also appears in most of the tests. The microstructural observations show a pronounced evolution of the porosity at the pellet center during the tests. A hyperbolic sine model which accounts for volume variations (pore compressibility) was therefore proposed to describe the behavior of UO2 on a large range of temperatures (1100 - 1700 °C) and strain rates (10-9-10-1 /s). The Finite Element simulations of the compression tests lead to results (maximum stress, axial and hoop strain distribution, porosity distribution) in good agreement with the measurements. The model was then assessed on a database of more than two hundred creep tests.

  12. Simulation of the strain rate sensitive flow behavior of SiC-particulate reinforced aluminum metal matrix composites

    OpenAIRE

    Tirtom, İsmail; Güden, Mustafa; Yıldız, Hasan

    2008-01-01

    Strain rate dependent compression mechanical behavior of an SiC-particulate reinforced Al (2024-O) metal matrix composite (MMC) with different particle volume fractions was numerically investigated at various strain rates. Calculations were performed using axisymmetric finite element unit cell model, in which an elastic SiC particle was embedded inside a strain rate sensitive viscoplastic Al matrix. Stress–strain curves of Al matrix material were derived from Split Hopkinson Pressure Bar expe...

  13. Quasi-Static and High Strain Rate Compressive Response of Injection-Molded Cenosphere/HDPE Syntactic Foam

    Science.gov (United States)

    Bharath Kumar, B. R.; Singh, Ashish Kumar; Doddamani, Mrityunjay; Luong, Dung D.; Gupta, Nikhil

    2016-07-01

    High strain rate compressive properties of high-density polyethylene (HDPE) matrix syntactic foams containing cenosphere filler are investigated. Thermoplastic matrix syntactic foams have not been studied extensively for high strain rate deformation response despite interest in them for lightweight underwater vehicle structures and consumer products. Quasi-static compression tests are conducted at 10-4 s-1, 10-3 s-1 and 10-2 s-1 strain rates. Further, a split-Hopkinson pressure bar is utilized for characterizing syntactic foams for high strain rate compression. The compressive strength of syntactic foams is higher than that of HDPE resin at the same strain rate. Yield strength shows an increasing trend with strain rate. The average yield strength values at high strain rates are almost twice the values obtained at 10-4 s-1 for HDPE resin and syntactic foams. Theoretical models are used to estimate the effectiveness of cenospheres in reinforcing syntactic foams.

  14. Exploration of mechanisms underlying the strain-rate-dependent mechanical property of single chondrocytes

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen, Trung Dung; Gu, YuanTong, E-mail: yuantong.gu@qut.edu.au [School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane, Queensland (Australia)

    2014-05-05

    Based on the characterization by Atomic Force Microscopy, we report that the mechanical property of single chondrocytes has dependency on the strain-rates. By comparing the mechanical deformation responses and the Young's moduli of living and fixed chondrocytes at four different strain-rates, we explore the deformation mechanisms underlying this dependency property. We found that the strain-rate-dependent mechanical property of living cells is governed by both of the cellular cytoskeleton and the intracellular fluid when the fixed chondrocytes are mainly governed by their intracellular fluid, which is called the consolidation-dependent deformation behavior. Finally, we report that the porohyperelastic constitutive material model which can capture the consolidation-dependent behavior of both living and fixed chondrocytes is a potential candidature to study living cell biomechanics.

  15. Compressive Strength of Hydrostatic-Stress-Sensitive Materials at High Strain-Rates

    Institute of Scientific and Technical Information of China (English)

    LI Q M; LU Y B

    2008-01-01

    Many engineering materials demonstrate dynamic enhancement of their compressive strength with the increase of strain-rate.which have been included in material models to improve the reliability of numerical Simulations of the material and structural responses Under impact and biasl tcads,The strain-rate effects on the dynamic Compressive strength of a range of engineering materials which behave in hydrostatic-stress-sensitive manner were investigated.It is concluded that the dynamic enhancement of the compressive strength of a hydrostatic-stress-sensitive material may include inertia-induced lateral confinement effects,which,as a non-strain-rate factor,may greatly enhance the compressive strength of these materials.Some empirical formulae based on the dynamic stress-strain measurements over-predict the strain-rate effects on the compressive strength of these hydrostatic-stress-sensitive materials,and thus may over-estimate the structural resistance to impact and blast lgads.leading fo non-conservative design of protective structures.

  16. Motor unit recruitment patterns 2: the influence of myoelectric intensity and muscle fascicle strain rate.

    Science.gov (United States)

    Hodson-Tole, Emma F; Wakeling, James M

    2008-06-01

    To effectively meet the force requirements of a given movement an appropriate number and combination of motor units must be recruited between and within muscles. Orderly recruitment of motor units has been shown to occur in a wide range of skeletal muscles, however, alternative strategies do occur. Faster motor units are better suited to developing force rapidly, and produce higher mechanical power with greater efficiency at faster shortening strain rates than slower motor units. As the frequency content of the myoelectric signal is related to the fibre type of the active motor units, we hypothesised that, in addition to an association between myoelectric frequency and intensity, there would be a significant association between muscle fascicle shortening strain rate and myoelectric frequency content. Myoelectric and sonomicrometric data were collected from the three ankle extensor muscles of the rat hind limb during walking and running. Myoelectric signals were analysed using wavelet transformation and principal component analysis to give a measure of the signal frequency content. Sonomicrometric signals were analysed to give measures of muscle fascicle strain and strain rate. The relationship between myoelectric frequency and both intensity and muscle fascicle strain rate was found to change across the time course of a stride, with differences also occurring in the strength of the associations between and within muscles. In addition to the orderly recruitment of motor units, a mechanical strategy of motor unit recruitment was therefore identified. Motor unit recruitment is therefore a multifactorial phenomenon, which is more complex than typically thought.

  17. Effects of strain rates on mechanical properties of limestone under high temperature

    Institute of Scientific and Technical Information of China (English)

    Tang Furong; Mao Xianbiao; Zhang Lianying; Yin Huiguang; Li Yan

    2011-01-01

    The experimental tests for limestone specimens at 700 ℃ in uniaxial compression were carried out to investigate the mechanical effects of loading rates on limestone by using a MTS810 rock mechanics servocontrolled testing system considering the loading rate as a variable.The mechanical properties of limestone such as the stress-strain curve,variable characteristics of peak strength and the modulus of elasticity of limestone were studied under the strain rates ranging from 1.1 × 10-s to 1.1 × 10-1 s-1.(1) Sharp decreases were shown for the peak strength and elastic modulus of limestone from 1.1 × 10-5 to 1.1 × 10 4 s-1 at 700 C as well as a downward trend was shown from 1.1 × 10 4 to 1.1 × 10-1 s-1with the rise of the strain rate.(2) The peak strain increased from 1.1 × 10-5 to 1.1 × 10-4 s-1,however,there was no obvious changes shown for the peak strain of limestone from 1.1 × 10-4 to 1.1 × 10-1 s-1.These results can nrovide valuable references for the rock blasting effect and design of mine.

  18. Effects of strain rate on the hot deformation behavior and dynamic recrystallization in China low activation martensitic steel

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Yuanyuan [School of Material Science and Engineering, Jiangsu University, Zhenjiang 212013 (China); Chen, Xizhang, E-mail: kernel.chen@gmail.com [School of Mechanical and Electrical Engineering, Wenzhou University, Wenzhou 325035 (China); Madigan, Bruce [Montana Tech, Butte, MT (United States); Cao, Hongyan [School of Material Science and Engineering, Jiangsu University, Zhenjiang 212013 (China); Konovalov, Sergey [Center for Collective Use Material Science, Siberian State Industrial University, Novokuznetsk (Russian Federation)

    2016-02-15

    Graphical abstract: - Highlights: • Average grain sizes of 1.8 μm are observed at strain rate of 10 s{sup −1}. • Peak stress value increased, but strain decreased with increasing of strain rate. • A catenuliform recrystallized occurred at a strain rate of 5 s{sup −1}. • DRX effect improved with increasing of deformation amounts. - Abstract: To investigate the effects of strain rate on dynamic recrystallization (DRX) behavior on China low activation martensitic steel, hot uniaxial compression tests with strain rates ranging from 0.1 s{sup −1} to 10 s{sup −1} and deformations amounts of 40% and 70% where conducted. The true stress–true strain curves were analyzed for the occurrence of DRX under the different strain rates and compressive deformation amounts. The steel microstructures were examined and linked to the observed stress-strain diagrams to study DRX. Results show that DRX was responsible for refining the grain structure over a wide range of strain rates under 70% deformation. However, significant DRX occurred only at the relatively low strain rate of 0.1 s{sup −1} under 40% deformation. The original elongated microstructure of the rolled plate from which the specimens were taken was replaced by dynamic recrystallization grains. At 70% deformation, the average grain size was 4.2 μm at a strain rate of 0.1 s{sup −1}, 2.5 μm at a strain rate of 5 s{sup −1}, 1.8 μm at a strain rate of 10 s{sup −1}. In conclusion, with increasing strain rate, the recrystallized grain size decreased and the peak stress increased.

  19. Energy absorption at high strain rate of glass fiber reinforced mortars

    Directory of Open Access Journals (Sweden)

    Fenu Luigi

    2015-01-01

    Full Text Available In this paper, the dynamic behaviour of cement mortars reinforced with glass fibers was studied. The influence of the addition of glass fibers on energy absorption and tensile strength at high strain-rate was investigated. Static tests in compression, in tension and in bending were first performed. Dynamic tests by means of a Modified Hopkinson Bar were then carried out in order to investigate how glass fibers affected energy absorption and tensile strength at high strain-rate of the fiber reinforced mortar. The Dynamic Increase Factor (DIF was finally evaluated.

  20. Strain rate sensitivity of nanoindentation creep in an AlCoCrFeNi high-entropy alloy

    Science.gov (United States)

    Jiao, Z. M.; Wang, Z. H.; Wu, R. F.; Qiao, J. W.

    2016-09-01

    Creep behaviors of an AlCoCrFeNi high-entropy alloy with the body-centered cubic structure were investigated by nanoindentation. The enhanced strain gradient induced by higher strain rate leads to decreased strain rate sensitivity during creep process. The present alloy exhibits excellent creep resistance, mainly due to its large entropy of mixing and highly distorted lattice structure.

  1. Determining the mechanical constitutive properties of metals as a function of strain rate and temperature: A combined experimental and modeling approach

    Energy Technology Data Exchange (ETDEWEB)

    I. M. Robertson; A. Beaudoin; J. Lambros

    2004-01-05

    OAK-135 Development and validation of constitutive models for polycrystalline materials subjected to high strain rate loading over a range of temperatures are needed to predict the response of engineering materials to in-service type conditions (foreign object damage, high-strain rate forging, high-speed sheet forming, deformation behavior during forming, response to extreme conditions, etc.). To account accurately for the complex effects that can occur during extreme and variable loading conditions, requires significant and detailed computational and modeling efforts. These efforts must be closely coupled with precise and targeted experimental measurements that not only verify the predictions of the models, but also provide input about the fundamental processes responsible for the macroscopic response. Achieving this coupling between modeling and experimentation is the guiding principle of this program. Specifically, this program seeks to bridge the length scale between discrete dislocation interactions with grain boundaries and continuum models for polycrystalline plasticity. Achieving this goal requires incorporating these complex dislocation-interface interactions into the well-defined behavior of single crystals. Despite the widespread study of metal plasticity, this aspect is not well understood for simple loading conditions, let alone extreme ones. Our experimental approach includes determining the high-strain rate response as a function of strain and temperature with post-mortem characterization of the microstructure, quasi-static testing of pre-deformed material, and direct observation of the dislocation behavior during reloading by using the in situ transmission electron microscope deformation technique. These experiments will provide the basis for development and validation of physically-based constitutive models, which will include dislocation-grain boundary interactions for polycrystalline systems. One aspect of the program will involve the dire ct

  2. Flow propagation velocity is not a simple index of diastolic function in early filling. A comparative study of early diastolic strain rate and strain rate propagation, flow and flow propagation in normal and reduced diastolic function

    Directory of Open Access Journals (Sweden)

    Skjaerpe Terje

    2003-04-01

    Full Text Available Abstract Background Strain Rate Imaging shows the filling phases of the left ventricle to consist of a wave of myocardial stretching, propagating from base to apex. The propagation velocity of the strain rate wave is reduced in delayed relaxation. This study examined the relation between the propagation velocity of strain rate in the myocardium and the propagation velocity of flow during early filling. Methods 12 normal subjects and 13 patients with treated hypertension and normal systolic function were studied. Patients and controls differed significantly in diastolic early mitral flow measurements, peak early diastolic tissue velocity and peak early diastolic strain rate, showing delayed relaxation in the patient group. There were no significant differences in EF or diastolic diameter. Results Strain rate propagation velocity was reduced in the patient group while flow propagation velocity was increased. There was a negative correlation (R = -0.57 between strain rate propagation and deceleration time of the mitral flow E-wave (R = -0.51 and between strain rate propagation and flow propagation velocity and there was a positive correlation (R = 0.67 between the ratio between peak mitral flow velocity / strain rate propagation velocity and flow propagation velocity. Conclusion The present study shows strain rate propagation to be a measure of filling time, but flow propagation to be a function of both flow velocity and strain rate propagation. Thus flow propagation is not a simple index of diastolic function in delayed relaxation.

  3. In vivo vascular wall shear rate and circumferential strain of renal disease patients.

    Science.gov (United States)

    Park, Dae Woo; Kruger, Grant H; Rubin, Jonathan M; Hamilton, James; Gottschalk, Paul; Dodde, Robert E; Shih, Albert J; Weitzel, William F

    2013-02-01

    This study measures the vascular wall shear rate at the vessel edge using decorrelation based ultrasound speckle tracking. Results for nine healthy and eight renal disease subjects are presented. Additionally, the vascular wall shear rate and circumferential strain during physiologic pressure, pressure equalization and hyperemia are compared for five healthy and three renal disease subjects. The mean and maximum wall shear rates were measured during the cardiac cycle at the top and bottom wall edges. The healthy subjects had significantly higher mean and maximum vascular wall shear rate than the renal disease subjects. The key findings of this research were that the mean vascular wall shear rates and circumferential strain changes between physiologic pressure and hyperemia that was significantly different between healthy and renal disease subjects.

  4. Rate dependent rheological stress-strain behavior of porous nanocrystalline materials

    Institute of Scientific and Technical Information of China (English)

    李慧; 周剑秋

    2008-01-01

    To completely understand the rate-dependent stress-strain behavior of the porous nanocrystalline materials,it is necessary to formulate a constitutive model that can reflect the complicated experimentally observed stress-strain relations of nanocrystalline materials.The nanocrystalline materials consisting grain interior and grain boundary are considered as viscoplastic and porous materials for the reasons that their mechanical deformation is commonly governed by both dislocation glide and diffusion,and pores commonly exist in the nanocrystalline materials.A constitutive law of the unified theory reflecting the stress-strain relations was established and verified by experimental data of bulk nanocrystalline Ni prepared by hydrogen direct current arc plasma evaporation method and hot compression.The effect of the evolution of porosity on stress-strain relations was taken into account to make that the predicted results can keep good agreements with the corresponding experimental results.

  5. Strain Rate and Anisotropic Microstructure Dependent Mechanical Behaviors of Silkworm Cocoon Shells.

    Directory of Open Access Journals (Sweden)

    Jun Xu

    Full Text Available Silkworm cocoons are multi-layered composite structures comprised of high strength silk fiber and sericin, and their mechanical properties have been naturally selected to protect pupas during metamorphosis from various types of external attacks. The present study attempts to gain a comprehensive understanding of the mechanical properties of cocoon shell materials from wild silkworm species Antheraea pernyi under dynamic loading rates. Five dynamic strain rates from 0.00625 s-1 to 12.5 s-1 are tested to show the strain rate sensitivity of the cocoon shell material. In the meantime, the anisotropy of the cocoon shell is considered and the cocoon shell specimens are cut along 0°, 45° and 90° orientation to the short axis of cocoons. Typical mechanical properties including Young's modulus, yield strength, ultimate strength and ultimate strain are extracted and analyzed from the stress-strain curves. Furthermore, the fracture morphologies of the cocoon shell specimens are observed under scanning electron microscopy to help understand the relationship between the mechanical properties and the microstructures of the cocoon material. A discussion on the dynamic strain rate effect on the mechanical properties of cocoon shell material is followed by fitting our experimental results to two previous models, and the effect could be well explained. We also compare natural and dried cocoon materials for the dynamic strain rate effect and interestingly the dried cocoon shells show better overall mechanical properties. This study provides a different perspective on the mechanical properties of cocoon material as a composite material, and provides some insight for bio-inspired engineering materials.

  6. Fibre-reinforced plastic composites - Determination of the in-plane shear stress/shear strain response, including the in-plane shear modulus and strength, by the plus or minus 45 degree tension test method

    CERN Document Server

    International Organization for Standardization. Geneva

    1997-01-01

    Fibre-reinforced plastic composites - Determination of the in-plane shear stress/shear strain response, including the in-plane shear modulus and strength, by the plus or minus 45 degree tension test method

  7. Contribution to the theoretical study of the plastic strain localization in porous materials; Contribution a l'etude theorique de la localisation plastique dans les poreux

    Energy Technology Data Exchange (ETDEWEB)

    Willot, F

    2007-01-15

    This work presents a study in theoretical mechanics, in the classical framework of homogenization of heterogeneous media. It addresses a notoriously problematical situation of non-linear behavior and infinite contrast between two phases, one of which is a plastic solid phase and the other one, the porosity of the medium. Its aim is to investigate how plastic strain localization manifests itself at the level of the overall effective behavior of the medium in presence of pores, and in particular in the non-trivial limit of small porosity. This question, important to the understanding of ductile damage, is examined both numerically and theoretically, in the restricted situation of bi-dimensional systems, and using a deformation theory approach of plasticity. The numerical investigations consist of quasi-exact computations of the strain and stress fields in the voided medium, by means of a Fast Fourier Transform method, and using a particular Green function. The theoretical approach makes use of exact solutions, which can be obtained in particular cases of a periodic void lattice, as well as of a recent 'second-order' nonlinear homogenization approach. The virtues of the latter are evaluated in two steps, first by studying the underlying linear anisotropic homogenization step (an essential ingredient), then by studying the nonlinear step itself. The nature and significance of the singularities of the theory which appear in the limit of small porosity, confirmed by numerical computations, are partly elucidated. Finally, original observations are presented as to the relation between plastic deformation patterns in an ideal disordered medium, and some features of the macroscopic strain/stress curve. (author)

  8. Numerical Derivation of Strain Rate Effects on Material Properties of Masonry with Solid Clay Bricks

    Institute of Scientific and Technical Information of China (English)

    WEI Xueying; HAO Hong

    2006-01-01

    In this paper,numerical method is used to study the strain rate effect on masonry materials.A typical unit of masonry is selected to serve as a representative volume element (RVE).Numerical model of RVE is established with detailed distinctive modeling of brick and mortar with their respective dynamic material properties obtained from laboratory tests.The behavior of brick and mortar are characterized by a dynamic damage model that accounts for rate-sensitive and pressuredependent properties of masonry materials.Dynamic loads of different loading rates are applied to RVE.The equivalent homogenized uniaxial compressive strength,threshold strain and elastic modulus in three directions of the masonry are derived from the simulated responses of the RVE.The strain rate effect on the masonry material with clay brick and mortar,such as the dynamic increase factor (DIF) of the ultimate strength and elastic modulus as a function of strain rate are derived from the numerical results.

  9. Effect of strain rate on shear properties and fracture characteristics of DP600 and AA5182-O sheet metal alloys

    Directory of Open Access Journals (Sweden)

    Rahmaan Taamjeed

    2015-01-01

    Full Text Available Shear tests were performed at strain rates ranging from quasi-static (.01 s−1 to 600 s−1 for DP600 steel and AA5182-O sheet metal alloys at room temperature. A miniature sized shear specimen was modified and validated in this work to perform high strain rate shear testing. Digital image correlation (DIC techniques were employed to measure the strains in the experiments, and a criterion to detect the onset of fracture based on the hardening rate of the materials is proposed. At equivalent strains greater than 20%, the DP600 and AA5182 alloys demonstrated a reduced work hardening rate at elevated strain rates. At lower strains, the DP600 shows positive rate sensitivity while the AA5182 was not sensitive to strain rate. For both alloys, the equivalent fracture strain and elongation to failure decreased with strain rate. A conversion of the shear stress to an equivalent stress using the von Mises yield criterion provided excellent agreement with the results from tensile tests at elevated strain rates. Unlike the tensile test, the shear test is not limited by the onset of necking so the equivalent stress can be determined over a larger range of strain.

  10. Influence of Strain Rate on Tensile Strength of Woven Geotextile in the Selected Range of Temperature

    Directory of Open Access Journals (Sweden)

    Stępień Sylwia

    2015-06-01

    Full Text Available Investigation of geosynthetics behaviour has been carried out for many years. Before using geosynthetics in practice, the standard laboratory tests had been carried out to determine basic mechanical parameters. In order to examine the tensile strength of the sample which extends at a constant strain rate, one should measure the value of the tensile force and strain. Note that geosynthetics work under different conditions of stretching and temperatures, which significantly reduce the strength of these materials. The paper presents results of the tensile test of geotextile at different strain rates and temperatures from 20 °C to 100 °C. The aim of this study was to determine the effect of temperature and strain rate on tensile strength and strain of the woven geotextile. The article presents the method of investigation and the results. The data obtained allowed us to assess the parameters of material which should be considered in the design of the load-bearing structures that work at temperatures up to 100 °C.

  11. Mechanical Characterization of Brain Tissue in Compression at Dynamic Strain Rates

    CERN Document Server

    Rashid, Badar; Gilchrist, Michael; 10.1016/j.jmbbm.2012.01.022

    2013-01-01

    Traumatic brain injury (TBI) occurs when local mechanical load exceeds certain tolerance levels for brain tissue. Extensive research has been done previously for brain matter experiencing compression at quasistatic loading; however, limited data is available to model TBI under dynamic impact conditions. In this research, an experimental setup was developed to perform unconfined compression tests and stress relaxation tests at strain rates < 90/s. The brain tissue showed a stiffer response with increasing strain rates, showing that hyperelastic models are not adequate. Specifically, the compressive nominal stress at 30% strain was 8.83 +/- 1.94, 12.8 +/- 3.10 and 16.0 +/- 1.41 kPa (mean +/- SD) at strain rates of 30, 60 and 90/s, respectively. Relaxation tests were also conducted at 10%-50% strain with the average rise time of 10 ms, which can be used to derive time dependent parameters. Numerical simulations were performed using one-term Ogden model with initial shear modulus mu_0 = 6.06 +/- 1.44, 9.44 +/-...

  12. Influence of Strain Rate on Tensile Strength of Woven Geotextile in the Selected Range of Temperature

    Science.gov (United States)

    Stępień, Sylwia; Szymański, Alojzy

    2015-06-01

    Investigation of geosynthetics behaviour has been carried out for many years. Before using geosynthetics in practice, the standard laboratory tests had been carried out to determine basic mechanical parameters. In order to examine the tensile strength of the sample which extends at a constant strain rate, one should measure the value of the tensile force and strain. Note that geosynthetics work under different conditions of stretching and temperatures, which significantly reduce the strength of these materials. The paper presents results of the tensile test of geotextile at different strain rates and temperatures from 20 °C to 100 °C. The aim of this study was to determine the effect of temperature and strain rate on tensile strength and strain of the woven geotextile. The article presents the method of investigation and the results. The data obtained allowed us to assess the parameters of material which should be considered in the design of the load-bearing structures that work at temperatures up to 100 °C.

  13. Effect of strain rate and water-to-cement ratio on compressive mechanical behavior of cement mortar

    Institute of Scientific and Technical Information of China (English)

    周继凯; 葛利梅

    2015-01-01

    Effects of strain rate and water-to-cement ratio on the dynamic compressive mechanical behavior of cement mortar are investigated by split Hopkinson pressure bar (SHPB) tests. 124 specimens are subjected to dynamic uniaxial compressive loadings. Strain rate sensitivity of the materials is measured in terms of failure modes, stress−strain curves, compressive strength, dynamic increase factor (DIF) and critical strain at peak stress. A significant change in the stress−strain response of the materials with each order of magnitude increase in strain rate is clearly seen from test results. The slope of the stress−strain curve after peak value for low water-to-cement ratio is steeper than that of high water-to-cement ratio mortar. The compressive strength increases with increasing strain rate. With increase in strain rate, the dynamic increase factor (DIF) increases. However, this increase in DIF with increase in strain rate does not appear to be a function of the water-to-cement ratio. The critical compressive strain increases with the strain rate.

  14. The dependence on pressure of the plastic flow of rocksalt in the temperature range 25-250° C: implications for the rate controlling mechanism

    Science.gov (United States)

    Muhammad, Nawaz; Spiers, Chris; De Bresser, Hans; Peach, Colin

    2014-05-01

    Despite the large body of data that already exists, the question what microphysical mechanisms govern plastic flow of natural rocksalt at in situ conditions has not yet been answered to full satisfaction. In particular, the exact mechanism controlling dislocation motion at relatively low temperature is still insufficiently understood. As a result, uncertainties exist regarding the appropriate mechanism-based flow-law for low temperature, hampering reliable extrapolation of lab creep data to in situ strain rates. Such extrapolation is required for the modelling of the long term behaviour of salt for geomechanical purposes (e.g. subsidence prognosis). Several dislocation models have been proposed to control plastic flow of rocksalt, such as dislocation climb, cross-slip and (impurity-controlled) glide, but none of these have been rigorously verified. One way to test which model is appropriate is by investigating the pressure dependence of flow of rocksalt. Dislocation glide is expected to be hardly affected by pressure, cross slip (controlled by constriction of partial dislocations) will become easier with increasing pressure, and dislocation climb will become more difficult. We performed conventional axi-symmetric compression tests on synthetic polycrystalline salt samples with an average grain size of 300 μm. The samples were dry, in order to eliminate the possible influence of pressure solution creep. The experiments were carried out at temperatures in the range 25-250° C, i.e. 0.28-0.48Tm, and at pressure ranging 50-600 MPa, which is a range not previously covered for polycrystalline rocksalt. Argon gas was used as the pressure medium. With confining pressure increasing from 50 to 600 MPa, the rocksalt remained of the same strength at RT, but became about 60% stronger at 125oC and about 80% stronger at 250oC at strain rate 10-6 s-1 (at 15% strain). Using a conventional (Dorn-type) power law to describe the mechanical behaviour, stress exponents (n) were found

  15. Temperature and strain rate effects on the piezoelectric charge production of PZT 95/5

    Science.gov (United States)

    Khan, Amnah S.; Proud, William G.

    2017-01-01

    To develop a better understanding of the piezoelectric ceramic lead zirconate titanate (PZT) 95/5, parameters including varying temperatures, porosities and strain rates have been studied. The effects on the charge output and fracture of poled PZT samples of different porosities have been investigated with compressive strain rates (10-4 - 10+3 s-1) using quasi-static loading equipment, drop-weight towers and Split Hopkinson Pressure Bars (SHPBs). The cylindrical specimens were of 4.4 mm diameter, thickness 0.8 - 4.4 mm, and density 7.3 - 8.3 g cm-3. The temperature range of -20 °C to +80 °C was achieved using purpose-built environmental chambers. The resulting stress-strain relationships are compared; all the samples ultimately displayed a brittle response at failure [1].

  16. Deformation and failure of OFHC copper under high strain rate shear compression

    Science.gov (United States)

    Ruggiero, Andrew; Testa, Gabriel; Bonora, Nicola; Iannitti, Gianluca; Persechino, Italo; Colliander, Magnus Hörnqvist

    2017-01-01

    Hat-shaped specimen geometries were developed to generate high strain, high-strain-rates deformation under prescribed conditions. These geometries offer also the possibility to investigate the occurrence of ductile rupture under low or negative stress triaxiality, where most failure models fail. In this work, three tophat geometries were designed, by means of extensive numerical simulation, to obtain desired stress triaxiality values within the shear region that develops across the ligament. Material failure was simulated using the Continuum Damage Model (CDM) formulation with a unilateral condition for damage accumulation and validated by comparing with quasi-static and high strain rate compression tests results on OFHC copper. Preliminary results seem to indicate that ductile tearing initiates at the specimen corner location where positive stress triaxiality occurs because of local rotation and eventually propagates along the ligament.

  17. Mechanical Behavior of MTMoCr under High Temperature and High Strain-rate

    Directory of Open Access Journals (Sweden)

    Zhengwei Dong

    2013-02-01

    Full Text Available MTMoCr is a kind of Mo-Cr alloy cast iron often used to make automobile panel dies. To study high-speed machining process of automobile panel dies, the material’s elastic modulus and rupture critical values of MTMoCr at 20℃-800℃ were studied based on the high temperature elongation test. The material’s stress-strain diagram at various temperatures set-points (20℃-500℃ and various strain-rates (500/s-5000/s were studied and the dynamic tensile yield strength values were obtained by dynamic SHPB (Split Hopkinson Pressure Bar high-speed compression test. The experimental results indicate that MTMoCr has heat resistance and its behavior is between toughness and brittleness materials. Its toughness is enhanced with temperature increasing. The strain-rate strengthening effect prevails over temperature softening effect.

  18. Mechanical characterization of particulate aluminum foams. Strain-rate, density and matrix alloy versus adhesive effects

    Energy Technology Data Exchange (ETDEWEB)

    Lehmhus, Dirk [ISIS Sensorial Materials Scientific Centre, University of Bremen (Germany); Baumeister, Joachim; Stutz, Lennart; Stoebener, Karsten [Fraunhofer IFAM Bremen (Germany); Schneider, Eduard [University of Bremen (Germany); Avalle, Massimiliano; Peroni, Lorenzo; Peroni, Marco [Dipartimento di Meccanica, Politecnico di Torino Vercelli (Italy)

    2010-07-15

    The study evaluates mechanical properties of APM particulate aluminum foams built up from adhesively bonded Al foam spheres. Foams of matrix alloy AlSi10 are compared, with PM AlSi7 foams used as reference. The influence of density is studied both for quasi-static and dynamic compressive loading in a range from {proportional_to}0.35 to 0.71 g cm{sup -3}. The effect of varying the bonding agent is evaluated for a single density and both strain rate levels by replacing the standard, high-strength epoxy-based adhesive with a polyamide of greatly increased ductility. The result is a clear shift of fracture events to higher strain levels, as well as the introduction of a strain-rate dependency of strength. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  19. Behavior of steel fiber-reinforced high-strength concrete at medium strain rate

    Institute of Scientific and Technical Information of China (English)

    Chujie JIAO; Wei SUN; Shi HUAN; Guoping JIANG

    2009-01-01

    Impact compression experiments for the steel fiber-reinforced high-strength concrete (SFRHSC) at medium strain rate were conducted using the split Hopkinson press bar (SHPB) testing method. The volume fractions of steel fibers of SFRHSC were between 0 and 3%. The experimental results showed that, when the strain rate increased from threshold value to 90 s-1, the maximum stress of SFRHSC increased about 30%, the elastic modulus of SFRHSC increased about 50%, and the increase in the peak strain of SFRHSC was 2-3 times of that in the matrix specimen. The strength and toughness of the matrix were improved remarkably because of the superposition effect of the aggregate high-strength matrix and steel fiber high-strength matrix. As a result, under impact loading, cracks developed in the SFRHSC specimen, but the overall shape of the specimen remained virtually unchanged. However, under similar impact loading, the matrix specimens were almost broken into small pieces.

  20. Strain coordination of quasi-plane-hypothesis for reinforced concrete beam strengthened by epoxy-bonded glass fiber reinforced plastic plate

    Institute of Scientific and Technical Information of China (English)

    ZENG Xian-tao; DING Ya-hong; WANG Xing-guo

    2006-01-01

    The testing of thirteen reinforced concrete (RC) beams strengthened by epoxy-bonded glass fiber reinforced plastic plate (GFRP) shows that the RC beam and the GFRP plate with epoxy bonding on it can work fairly well in coordination to each other. But there is relative slipping between RC beam and GFRP plate. And the strain of GFRP and steel rebar of RC beam satisfies the quasi-plane-hypothesis, that is, the strain of longitudinal fiber that parallels to the neutral axis of plated beam within the scope of effective height (h0) of the cross section is in direct proportion to the distance from the fiber to the neutral axis. The strain of GFRP and steel rebar satisfies the equation: εCFRP = Kεsteel.

  1. INFLUENCES OF EDGING ROLL SHAPE ON THE PLASTIC STRAIN DISTRIBUTION OF SLAB DURING MULTI-PASS V-H ROLLING PROCESS

    Institute of Scientific and Technical Information of China (English)

    H.L. Yu; X.H. Liu; C.S. Li; X.M. Zhao; Y. Kusaba

    2006-01-01

    Multi-pass slab vertical-horizontal (V-H) rolling process with variable edging roll shape have been simulated with explicit dynamic finite element method and updating geometric method. The distributions of plastic strain contour in slab during rolling process with different edging roll and under different rolling stage have been obtained. The results show that there exist two thin strain assembling zones in slab when the flat edging roll is used, and there just exist one strain assembling zone in slab when the edging roll with groove is used. And compared the deformation equality between flat edging roll and edging rollwith groove, the lateris better than the former, which supplies the theory prove to the slab deformation distribution during V-H rolling process and is helpful for predicting the slab texture.

  2. Strain rate effects on the mechanical behavior of two Dual Phase steels in tension

    Science.gov (United States)

    Cadoni, E.; Singh, N. K.; Forni, D.; Singha, M. K.; Gupta, N. K.

    2016-05-01

    This paper presents an experimental investigation on the strain rate sensitivity of Dual Phase steel 1200 (DP1200) and Dual Phase steel 1400 (DP1400) under uni-axial tensile loads in the strain rate range from 0.001 s-1 to 600 s-1. These materials are advanced high strength steels (AHSS) having high strength, high capacity to dissipate crash energy and high formability. Flat sheet specimens of the materials having gauge length 10 mm, width 4 mm and thickness 2 mm (DP1200) and 1.25 mm (DP1400), are tested at room temperature (20∘C) on electromechanical universal testing machine to obtain their stress-strain relation under quasi-static condition (0.001 s-1), and on Hydro-Pneumatic machine and modified Hopkinson bar to study their mechanical behavior at medium (3 s-1, and 18 s-1) and high strain rates (200 s-1, 400 s-1, and 600 s-1) respectively. Tests under quasi-static condition are performed at high temperature (200∘C) also, and found that tensile flow stress is a increasing function of temperature. The stress-strain data has been analysed to determine the material parameters of the Cowper-Symonds and the Johnson-Cook models. A simple modification of the Johnson-Cook model has been proposed in order to obtain a better fit of tests at high temperatures. Finally, the fractographs of the broken specimens are taken by scanning electron microscope (SEM) to understand the fracture mechanism of these advanced high strength steels at different strain rates.

  3. The compressive behaviour and constitutive equation of polyimide foam in wide strain rate and temperature

    Directory of Open Access Journals (Sweden)

    Yoshimoto Akifumi

    2015-01-01

    Full Text Available These days, polymer foams, such as polyurethane foam and polystyrene foam, are used in various situations as a thermal insulator or shock absorber. In general, however, their strength is insufficient in high temperature environments because of their low glass transition temperature. Polyimide is a polymer which has a higher glass transition temperature and high strength. Its mechanical properties do not vary greatly, even in low temperature environments. Therefore, polyimide foam is expected to be used in the aerospace industry. Thus, the constitutive equation of polyimide foam that can be applied across a wide range of strain rates and ambient temperature is very useful. In this study, a series of compression tests at various strain rates, from 10−3 to 103 s−1 were carried out in order to examine the effect of strain rate on the compressive properties of polyimide foam. The flow stress of polyimide foam increased rapidly at dynamic strain rates. The effect of ambient temperature on the properties of polyimide foam was also investigated at temperature from − 190 °C to 270°∘C. The flow stress decreased with increasing temperature.

  4. Measurements of Creep Internal Stress Based on Constant Strain Rate and Its Application to Engineering

    Institute of Scientific and Technical Information of China (English)

    TAO Wen-liang; WEI Tao

    2006-01-01

    This research is carried out on the basis of Constant Strain Rate(CSR) to measure creep internal stress. Measurements of creep internal stress are conducted on the material test machine by using the CSR method. A mathematical model of creep internal stress is also proposed and its application is presented in this paper.

  5. Recent Achievements in Developing Low Temperature and High Strain Rate Superplastic Materials

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    This paper is to briefly outline our recent activities in developing low temperature or high strain rate superplastic materials, including aircraft-used and general-purpose Al- and Mg-base alloys or composites, as well as Ti3Al base intermetallic alloys. The processing routes applied included the thermomechanical treatment, equal channel angular pressing and other extrusion or forging methods.

  6. The influence of strain rate on the interfacial fracture toughness between PVB and laminated glass

    Science.gov (United States)

    Iwasaki, R.; Sato, C.

    2006-08-01

    This paper presents the experimental results of high speed tests using laminated safety glass to determine the interfacial fracture toughness between PVB (polyvinyl butyral) sheets and glass plates. Low-speed tensile test of PVB was carried out firstly. PVB shows a non-linear visco-elastic property. The property was described using a non-linear visco-elastic model. The visco-elastic parameters were calculated to compare the experimentally obtained stress-strain curves and the results of simulation. A simple fracture-mechanical model for PVB laminated glass was conducted to determine the energy release rate G. The fracture toughness Gc of the PVB laminated glass specimens were calculated from both the results of low-speed tensile tests and the equation for the energy release rate. The strain-stress curves of PVB under high strain rates are totally different from those of the low speed tests. The phenomenon can be explained from the phase transition due to the difference of strain rates because the mechanical properties of PVB changes from visco-elastic to glassy behavior. The fracture toughness of PVB laminated glass was calculated from the experimental results of high speed tests. Fracture energy was defined and also compared to the fracture toughness.

  7. Heart wall motion analysis by dynamic 3D strain rate imaging from tissue Doppler echocardiography

    Science.gov (United States)

    Hastenteufel, Mark; Wolf, Ivo; de Simone, Raffaele; Mottl-Link, Sibylle; Meinzer, Hans-Peter

    2002-04-01

    The knowledge about the complex three-dimensional (3D) heart wall motion pattern, particular in the left ventricle, provides valuable information about potential malfunctions, e.g., myocardial ischemia. Nowadays, echocardiography (cardiac ultrasound) is the predominant technique for evaluation of cardiac function. Beside morphology, tissue velocities can be obtained by Doppler techniques (tissue Doppler imaging, TDI). Strain rate imaging (SRI) is a new technique to diagnose heart vitality. It provides information about the contraction ability of the myocardium. Two-dimensional color Doppler echocardiography is still the most important clinical method for estimation of morphology and function. Two-dimensional methods leads to a lack of information due to the three-dimensional overall nature of the heart movement. Due to this complex three-dimensional motion pattern of the heart, the knowledge about velocity and strain rate distribution over the whole ventricle can provide more valuable diagnostic information about motion disorders. For the assessment of intracardiac blood flow three-dimensional color Doppler has already shown its clinical utility. We have developed methods to produce strain rate images by means of 3D tissue Doppler echocardiography. The tissue Doppler and strain rate images can be visualized and quantified by different methods. The methods are integrated into an interactively usable software environment, making them available in clinical everyday life. Our software provides the physician with a valuable tool for diagnosis of heart wall motion.

  8. Strain rate sensitivity of the tensile strength of two silicon carbides: experimental evidence and micromechanical modelling

    Science.gov (United States)

    Zinszner, Jean-Luc; Erzar, Benjamin; Forquin, Pascal

    2017-01-01

    Ceramic materials are commonly used to design multi-layer armour systems thanks to their favourable physical and mechanical properties. However, during an impact event, fragmentation of the ceramic plate inevitably occurs due to its inherent brittleness under tensile loading. Consequently, an accurate model of the fragmentation process is necessary in order to achieve an optimum design for a desired armour configuration. In this work, shockless spalling tests have been performed on two silicon carbide grades at strain rates ranging from 103 to 104 s-1 using a high-pulsed power generator. These spalling tests characterize the tensile strength strain rate sensitivity of each ceramic grade. The microstructural properties of the ceramics appear to play an important role on the strain rate sensitivity and on the dynamic tensile strength. Moreover, this experimental configuration allows for recovering damaged, but unbroken specimens, giving unique insight on the fragmentation process initiated in the ceramics. All the collected data have been compared with corresponding results of numerical simulations performed using the Denoual-Forquin-Hild anisotropic damage model. Good agreement is observed between numerical simulations and experimental data in terms of free surface velocity, size and location of the damaged zones along with crack density in these damaged zones. This article is part of the themed issue 'Experimental testing and modelling of brittle materials at high strain rates'.

  9. TRP 9904 - Constitutive Behavior of High Strength Multiphase Sheel Steel Under High Strain Rate Deformation

    Energy Technology Data Exchange (ETDEWEB)

    David Matlock; John Speer

    2005-03-31

    The focus of the research project was to systematically assess the strain rate dependence of strengthening mechanisms in new advanced high strength sheet steels. Data were obtained on specially designed and produced Duel Phase and TRIP steels and compared to the properties of automotive steels currently in use.

  10. Fracture and strain rate behavior of airplane fuselage materials under blast loading

    NARCIS (Netherlands)

    Mediavilla Varas, J.; Soetens, F.; Kroon, E.; Aanhold, J.E. van; Meulen, O.R. van der; Sagimon, M.

    2010-01-01

    The dynamic behavior of three commonly used airplane fuselage materials is investigated, namely of Al2024-T3, Glare-3 and CFRP. Dynamic tensile tests using a servo-hydraulic and a light weight shock testing machine (LSM) have been performed. The results showed no strain rate effect on Al2024-T3 and a

  11. Effects of reduced-rate methyl bromide applications under conventional and virtually impermeable plastic film in perennial crop field nurseries.

    Science.gov (United States)

    Hanson, Bradley D; Gerik, James S; Schneider, Sally M

    2010-08-01

    Producers of perennial crop nursery stock in California use preplant soil fumigation to meet state phytosanitary requirements. Although methyl bromide (MB) has been phased out in many agricultural industries, it is still the preferred treatment in the perennial nursery industry and is used under Critical Use Exemptions and Quarantine/Preshipment provisions of the Montreal Protocol. The present research was conducted to evaluate reduced-rate MB applications sealed with conventional and low-permeability plastic films compared with the primary alternative material. Reduced rates (100-260 kg ha(-1)) of MB applied in combination with chloropicrin (Pic) and sealed with a low-permeability plastic film provided weed and nematode control similar to the industry standard rate of 392 kg ha(-1) MB:Pic (98:2) sealed with high-density polyethylene (HDPE) film. However, the primary alternative chemical, 1,3-dichloropropene (1,3-D), tended to provide slightly lower pest control even on sites with relatively low plant parasitic nematode, soil-borne pathogen and weed pest pressure. If California regulations change to allow the use of low-permeability films in broadcast fumigant applications, the results of this research suggest that reduced rates of MB in perennial crop nurseries could serve as a bridge strategy until more technically, economically and environmentally acceptable alternatives are developed. Published 2010 by John Wiley & Sons, Ltd.

  12. Longevity, growth rate and related traits among strains of Tribolium castaneum.

    Science.gov (United States)

    Soliman, M H; Lints, F A

    1975-01-01

    Longevity of eight laboratory strains of the flour beetle Tribolium castaneum, with various geographic backgrounds, was studied under constant laboratory conditions of 33 degrees C and 70% relative humidity in standard medium (95% whole wheat flour and 5% dried yeast) during a period of 227 days starting from the egg stage. The eggs were collected from the same parents, first a few days after emergence and afterwards at intervals of 13, 9, 10 and 11 days. Mean survival time (MST) was found to be strain-specified. It ranges from 128.6 days for KJ (Kyoto, Japan) to 174.2 days for ES (Edinburgh, Scotland). MST was highly correlated with the percentage of adults alive after 227 days, which did not change the ranking order of strain longevity. Parental age had no effect on longevity. The mean adult longevity of the strains was correlated with the available data on adult weight, growth rate, viability and productivity. There was no relationship between adult weight and longevity. LIfe span was found to depend on growth rate (measured as 13-day larval weight), percent viability (from 13-day larvae to adulthood) and productivity. Developmental time was also found to influence adult life span within certain limits (two extreme strains deviated). The data suggest that ageing and death in T. castaneum is under genetic control and support the idea that ageing, allied to development, is genetically controlled.

  13. A real-time heat strain risk classifier using heart rate and skin temperature.

    Science.gov (United States)

    Buller, Mark J; Latzka, William A; Yokota, Miyo; Tharion, William J; Moran, Daniel S

    2008-12-01

    Heat injury is a real concern to workers engaged in physically demanding tasks in high heat strain environments. Several real-time physiological monitoring systems exist that can provide indices of heat strain, e.g. physiological strain index (PSI), and provide alerts to medical personnel. However, these systems depend on core temperature measurement using expensive, ingestible thermometer pills. Seeking a better solution, we suggest the use of a model which can identify the probability that individuals are 'at risk' from heat injury using non-invasive measures. The intent is for the system to identify individuals who need monitoring more closely or who should apply heat strain mitigation strategies. We generated a model that can identify 'at risk' (PSI 7.5) workers from measures of heart rate and chest skin temperature. The model was built using data from six previously published exercise studies in which some subjects wore chemical protective equipment. The model has an overall classification error rate of 10% with one false negative error (2.7%), and outperforms an earlier model and a least squares regression model with classification errors of 21% and 14%, respectively. Additionally, the model allows the classification criteria to be adjusted based on the task and acceptable level of risk. We conclude that the model could be a valuable part of a multi-faceted heat strain management system.

  14. Strain rate dependence of the flow stress and work hardening of {gamma}`

    Energy Technology Data Exchange (ETDEWEB)

    Ezz, S.S. [Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH (United Kingdom); Sun, Y.Q. [Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH (United Kingdom); Hirsch, P.B. [Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH (United Kingdom)

    1995-02-15

    The strain rate ({epsilon}) sensitivity of the flow stress ({tau}), {beta}=({delta}{tau}/{delta} ln{epsilon}), of crystals of {gamma}` in the temperature (T) range of the yield stress anomaly obeys a Cottrell-Stokes law when plotted against {tau}{sub h}={tau}-{tau}{sub y}, where {tau}{sub y} is the yield stress at 0.01% strain. The slopes are approximately 1%, decrease with increasing T and are approximately independent of orientation. {tau}{sub h} is due to work hardening and depends on the prestrain {epsilon}, {epsilon} and T. Transmission electron microscopy observations suggest that at 2% strain at 600 K and 720 K, {tau}{sub h} and {beta} are mainly controlled by forest obstacles. At 600 K, the forest consists largely of [101] dislocations on the (010) cross slip plane threading the (111) planes and generated by bowing of the [101] primary screws (Kear-Wilsdorf locks). At 720 K, the forest is non-uniform and consists of [101] on (010), primary cube [110] on (001) and secondary octahedral slip dislocations. At room temperature, the strength of the obstacles is weaker and it is suggested that they are mainly jogs on edge dislocations generated by cross slip of screw segments. At 2% strain, fine slip on (010) and (001) contributes increasingly to strain with increasing T and this correlates with the decrease in the work-hardening rate. ((orig.))

  15. Effects of strain rate and confining pressure on the deformation and failure of shale

    Energy Technology Data Exchange (ETDEWEB)

    Cook, J.M. (Schlumberger Cambridge Research (GB)); Sheppard, M.C. (Anadrill/Schlumberger (US)); Houwen, O.H. (Sedco Forex (FR))

    1991-06-01

    Previous work on shale mechanical properties has focused on the slow deformation rates appropriate to wellbore deformation. Deformation of shale under a drill bit occurs at a very high rate, and the failure properties of the rock under these conditions are crucial in determining bit performance and in extracting lithology and pore-pressure information from drilling parameters. Triaxial tests were performed on two nonswelling shales under a wide range of strain rates and confining and pore pressures. At low strain rates, when fluid is relatively free to move within the shale, shale deformation and failure are governed by effective stress or pressure (i.e., total confining pressure minus pore pressure), as is the case for ordinary rock. If the pore pressure in the shale is high, increasing the strain rate beyond about 0.1%/sec causes large increases in the strength and ductility of the shale. Total pressure begins to influence the strength. At high stain rates, the influence of effective pressure decreases, except when it is very low (i.e., when pore pressure is very high); ductility then rises rapidly. This behavior is opposite that expected in ordinary rocks. This paper briefly discusses the reasons for these phenomena and their impact on wellbore and drilling problems.

  16. Transform method for laser speckle strain-rate measurements in biological tissues and biomaterials

    Science.gov (United States)

    Kirkpatrick, Sean J.

    1999-03-01

    Laser speckle strain measurements in biological tissues and some synthetic biomaterials, such as translucent dental composites and ceramics, are often complicated by the physical properties of the materials. For example, speckles generated by illuminating soft biological tissue with laser light are subject to rapid decorrelation due to the Brownian movement of water and scattering particles in the tissues and to cellular motions. In addition, the penetration of the laser beam into the tissue or translucent biomaterial results in multiple scattering and a complete depolarization of the speckle field. This may complicate the evaluation of the strain field when a force is applied to the material because the speckle pattern shift is providing information from the surface of the material as well as from the bulk sample, where the strains may or may not be the same as on the surface. This paper presents a variation of a speckle processing scheme originally called the `Transform Method' for evaluating both surface and bulk strain rates and total strains in biological tissues and translucent biomaterials. The method is not a correlation-based technique, but instead relies upon 2D frequency transforms of time series of 1D speckle pattern records stacked into 2D arrays. The method is insensitive to speckle field depolarization and, compared to correlation-based techniques, is relatively insensitive to speckle decorrelation. Strain rates and total in-plane strains were measured in both hard (cortical bone) and soft (artery segments) biological tissues and in translucent biomaterials (dental ceramics). Potential applications to medical diagnostics and biomaterials science are also discussed.