Investigations of shock-induced deformation and dislocation mechanism by a multiscale discrete dislocation plasticity model

There are many theoretical and computational investigations devoted to the dislocation mechanism based crystal plasticity under static or quasi-static conditions. However, the dislocation behavior, specifically the nucleation and multiplication of dislocations, remains unclear in crystal under shock loading. In this paper, the dislocation mechanism in single crystalline copper under shock loading is investigated through a multiscale numerical model, which couples discrete dislocation dynamics (DDD) with explicit finite element (FE) analyses. Firstly, since the homogeneous nucleation (HN) of dislocations is considered as the dominant dislocation generation mechanism at extremely high strain rates, the typical parameters of HN are obtained by systematic molecular dynamics (MD) simulations, which include critical shear stress, saturation time, stable density, etc. Then, these parameters are implemented into DDD-FE model by a coarse grained method. It can remarkably improve the computational efficiency without loss of typical dislocation characters. The interactions between shock wave and dislocations are studied in detail. Band-like dislocation walls and their shielding effect on other dislocations are observed during the shock wave propagation. The simulation results are in good agreement with experimental observations. It is also found that both fast HN and avalanche-like dislocation multiplication get involved and lead to the softening of shear stress. Finally, by comparing the dynamic behavior under different impact speeds, a threshold speed around 1000 m/s for the dislocation dominant mechanism is proposed from the computations in this work. Beyond this speed, the effect of other defects such as stacking fault and twinning would be prominent. (C) 2017 Elsevier B.V. All rights reserved.