Elastic anisotropy of shocked aluminum single crystals: Use of molecular dynamics simulations

Abstract

Molecular dynamics (MD) calculations were used to examine shock wave propagation along [100], [111], and [110] directions in aluminum single crystals. Four different embedded-atom method (EAM) potentials were used to obtain wave profiles in ideal (defect-free) crystals shocked to peak longitudinal stresses approaching 13 GPa. Due to the lack of defects in the simulated crystals, the peak stresses considered, and the short time scales examined, inelastic deformation was not observed in the MD simulations. Time-averaged and spatially averaged continuum variables were determined from the MD simulations to compare results from different potentials and to provide a direct comparison with results from nonlinear elastic continuum calculations that incorporated elastic constants up to fourth order. These comparisons provide a basis for selecting the optimal potential from among the four potentials examined. MD results for shocks along the [100] direction show significant differences for stresses and densities determined from simulations using different EAM potentials. In contrast, the continuum variables for shocks along the [111] and [110] directions show smaller differences for three of the four potentials examined. Comparisons with the continuum calculations show that the potential developed recently by Winey, Kubota, and Gupta [Modell. Simul. Mater. Sci. Eng. 17, 055004 (2009)] provides the best overall agreement between the MD simulations and the continuum calculations. As such, this potential is recommended for MD simulations of shock wave propagation in aluminum single crystals. Extending the current findings to elastic-plastic deformation would be desirable. More generally, our work demonstrates that MD simulations of elastic shock waves in defect-free single crystals, in combination with nonlinear elastic continuum calculations, constitute an important step in establishing the applicability of classical MD potentials for simulations involving dynamic compression.