Deformation mechanisms in magnesium single crystal : multi-scale dislocation dynamics analyses -

Abstract

Hexagonal-closed packed materials (HCP) materials has attracted interest recently due to their unique physical and mechanical properties. The low density and the high strength to weight ratio of such materials make them excellent candidates to save structural weight and consequently fuel consumption in both automotive and aircraft fields. However, the deformation behavior of HCP metals hasn’t been completely understood as prior work still lack a detailed understanding on the activation of slip planes and twinning. In addition, the work-hardening behavior and the effect of size and strain rate are not yet well-established. This work aims at investigating the deformation mechanisms in magnesium single crystals using Multiscale Dislocation Dynamics Plasticity (MDDP) model. In particular, we focus on studying the effect of dislocation mobility dependence on the dislocation character and on modeling the deformation behavior under different orientations, and for different sizes, strain rates and loading conditions. Our results show that the experimentally observed hardening behavior can be reproduced by using linear interpolation of the mobility such that screw segments are stationary and edge segments are highly mobile. In addition, simulations for size effect, on yield stress and hardening behavior, for finite crystal are in good agreement with recent experimental results. Also, a one fourth power law exponent, similar to the one developed by Swegle and Grady (1985) was obtained for the variation of the strain rate with yield stress. Moreover, shock loading results are consistent with recently published experiments regarding particle velocity history, and the stress profile. These findings provide a better understanding of the complicated plastic deformation in HCP crystals, in particular, Mg single crystals.