Homogeneous dislocation nucleation in cyclotrimethylene trinitramine under shock loading

Abstract

The propagation of shock waves normal to (111) in the energetic molecular crystal cyclotrimethylene trinitramine (RDX) has been studied using large-scale molecular dynamics simulations. Partial dislocation loops with Burgers vector 0.16[010] are nucleated homogeneously on (001) at Rankine–Hugoniot shock pressures greater than 1.3 GPa. Calculations of the [010] cross-section of the (001) generalized stacking fault energy surface as a function of applied pressure along [001] reveals that the stacking fault enclosed by the partial dislocation loops is rendered metastable by a stress-induced change in molecular conformation. Furthermore, large-scale molecular dynamics simulations performed on quasi-two-dimensional (111)-oriented single crystals show a two-wave elastic-plastic response with a “galloping” plastic wave. We propose that the onset of homogeneous dislocationnucleation accounts for the abrupt change in the elastic-plastic response of macroscopic (111)-oriented RDX single crystals observed in recent experiments by giving rise to an anomalous plastic hardening.