Abstract
Till now, it was widely believed that the dislocation strengthening coefficients used in the Taylor-like relation were universal for a given crystallographic class of materials. In the present study, it is shown that this is actually untrue because of two effects that influence the strength of interactions between slip systems, namely the value of the Poisson ratio and the occurrence of doubly degenerated, asymmetric, junction configurations. New strengthening coefficient values for reactions between slip systems were determined using dislocation dynamics simulations on five representative FCC metals, plus germanium, and on five BCC transition metals for {110} and {112} slip systems at high homologous temperatures. The value of the Poisson ratio affects all the strengthening coefficients to various extents ranging from small to substantial. The effects of configuration asymmetry and Poisson's ratio are more marked in BCC metals than in FCC metals. These two major effects arise from a number of concurring dislocation mechanisms, which are discussed in some detail. It is expected that the use of accurate material-dependent coefficients will notably improve the predictive ability of current models for strain hardening.
Highlights
The dislocation strengthening relation, which relates the critical stress for the onset of slip to the square root of the total density, is an almost universal building block for dislocation-based models of plastic flow [1,2]
This section discusses first two effects that were neglected till the effect of the Poisson ratio, which affects all materials in the Scattergood-Bacon approximation, and an asymmetry effect, which affects some particular reactions
In most previous computations of strengthening coefficients in FCC metals, copper was taken as a model material [8,9,11] and typical values close to n 1⁄4 1/3 were used for its Poisson's ratio
Summary
The dislocation strengthening (or Taylor-like) relation, which relates the critical stress for the onset of slip to the square root of the total density, is an almost universal building block for dislocation-based models of plastic flow [1,2]. The storage-recovery model initially proposed by Kocks [4] was generalized by Teodosiu et al [5] in order to express the contribution of each slip system to dislocation storage and recovery. Such generalized formulations are widely used since they can be solved using crystal plasticity finite element codes. Dislocation dynamics (DD) simulations further contributed to significantly improve their predictive ability by providing numerical values for a number of coefficients (see e.g., [6,7])
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