Homogeneous dislocation nucleation in cyclotrimethylene trinitramine under shock loading

MJ Cawkwell and KJ Ramos and DE Hooks and TD Sewell, JOURNAL OF APPLIED PHYSICS, 107, 063512 (2010).

DOI: 10.1063/1.3305630

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 0.16010 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 dislocation nucleation 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.

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