The material properties of OFHC copper film was investigated with the High-Speed Material Micro Testing Machine (HSMMTM) at the high strain rates. The rate-dependent stress-strain curves from the experiment and the Johnson−Cook curve fitting showed large discrepancies as the plastic strain increases since the constitutive model implies no rate-dependent strain hardening effect. A new constituti...

-Dislocation theory is used to invoke a strain gradient theory of rate independent plasticity. Hardening is assumed to result from the accumulation of both randomly stored and geometrically necessary dislocations. The density of the geometrically necessary dislocations scales with the gradient of plastic strain. A deformation theory of plasticity is introduced to represent in a phenomenological...

advanced high strength steels (ahss) have recently attracted great attention because of their superior mechanical properties. a modern group of these steels, known as twinning induced plasticity (twip) steels, shows a unique combination of strength and ductility even at high rates of strain. in order to examine the functionality of such steels in dynamic loading conditions, their mechanical beh...

We analyze the stability of homogeneous simple tensile/compressive deformations of an isotropic heat-conducting thermoviscoplastic bar by studying the growth of infinitesimal perturbations superimposed upon a homogeneous deformation. The smallest axial strain at which the superimposed perturbation has a positive initial growth rate is called the instability strain. Two criteria are used to dete...

Advanced high strength steels (AHSS) have recently attracted great attention because of their superior mechanical properties. A modern group of these steels, known as twinning induced plasticity (TWIP) steels, shows a unique combination of strength and ductility even at high rates of strain. In order to examine the functionality of such steels in dynamic loading conditions, their mechanical beh...

In this paper we present a modeling approach to bridge the atomistic with macroscopic scales in crystalline materials. The methodology combines identification and modeling of the controlling unit processes at microscopic level with the direct atomistic determination of fundamental material properties. These properties are computed using a many body Force Field derived from ab initio quantum-mec...

We study thermomechanical deformations of a viscoplastic body deformed in simple shear. The e€ect of material elasticity is neglected but that of work hardening, strain-rate hardening, thermal softening, and strain-rate gradients is considered. The consideration of strain-rate gradients introduces a material characteristic length into the problem. A homogeneous solution of the governing equatio...

In this work, dynamic mechanical properties of three high-manganese steels with TRIP/TWIP or fully TWIP characteristics are studied. High strain rate experiments in the range of true strain rates between ~500 and 1800 /s are conducted using a dynamic torsional testing setup. All the three steels show a positive strain rate sensitivity in the intermediate range of strain rates (up to 500 /s). Bu...

in this work, dynamic mechanical properties of three high-manganese steels with trip/twip or fully twip characteristics are studied. high strain rate experiments in the range of true strain rates between ~500 and 1800 /s are conducted using a dynamic torsional testing setup. all the three steels show a positive strain rate sensitivity in the intermediate range of strain rates (up to 500 /s). bu...

The present paper is concerned with the development of a micromechanical model of the hardening, rate-sensitivity and thermal softening of b.c.c. crystals. In formulating the model we specifically consider the following unit processes: double-kink formation and thermally activated motion of kinks; the close-range interactions between primary and forest dislocations, leading to the formation of ...