A micromechanical model of hardening, rate sensitivity and thermal softening in BCC single crystals

Abstract

The present paper is concerned with the development of a micromechanical model of the hardening, rate-sensitivity and thermal softening of bcc crystals. In formulating the model, we speciÿcally 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 jogs; the percolation motion of dislocations through a random array of forest dislocations introducing short-range obstacles of di erent strengths; dislocation multiplication due to breeding by double cross-slip; and dislocation pair annihilation. The model is found to capture salient features of the behavior of Ta crystals such as: the dependence of the initial yield point on temperature and strain rate; the presence of a marked stage I of easy glide, specially at low temperatures and high strain rates; the sharp onset of stage II hardening and its tendency to shift towards lower strains, and eventually disappear, as the temperature increases or the strain rate decreases; the parabolic stage II hardening at low strain rates or high temperatures; the stage II softening at high strain rates or low temperatures; the trend towards saturation at high strains; the temperature and strain-rate dependence of the saturation stress; and the orientation dependence of the hardening rate.

Density functional theory and molecular dynamics studies of the energetics and kinetics of electroactive polymers: PVDF and P(VDF-TrFE)

“…(3)] is very general in nature and can describe various mechanisms such as free volume-based deformation in metallic glasses 24,25 and dislocation-based single crystal plasticity. 26,27 The resulting effective volume in the parallel case is V 0 = 281.4 Å 3 and in the perpendicular direction is 116.3 Å 3 ; the characteristic frequencies ␥ 0 are 1.33ϫ 10 10 1/s and 0.17ϫ 10 10 1 / s in the parallel and perpendicular directions, respectively. As expected, we find that the direction of easy slip has a larger characteristic frequency [␥ 0 is proportional to exp ͑⌬G / k b T͒ where ⌬G is an activation barrier [24][25][26] ] and a larger effective volume.…”

Experimental characterization and mechanical behaviour modelling of molybdenum–titanium carbide composite for high temperature applications

“…The understanding of these mechanisms will be investigated through simulation of compressive tests by using a crystalline approach implemented in ABAQUS finite element code. Such modellings have shown their efficiency to determine the nondirectly measurable physical mechanisms [1][2][3][4][5][6][7][8]. In this modelling, the determination of material parameters, based on experimental characterization, will be described in this paper.…”

Grain Size Effect on Deformation Mechanisms of Nanocrystalline bcc Metals

“…Since the core of the ½[111] screw dislocation is spread onto three different slip planes, this makes it three dimensional (3D) and very hard to slip on any of the slip planes. Consequently, the slip of the screw dislocations in bcc metals is believed to proceed via side movements of edge dislocation kinks [26][27][28][29], which leads to a higher strain rate sensitivity in bcc metals. On the other hand, molecular are dark-field images using g [1 10] to image, while (f) is a bright-field image using g [1 12] to image.…”