High pressure effects on plastic deformation of molecular crystals

The plastic deformation of energetic molecular crystals is of importance for reaction initiation and detonation. Void collapse and shear localization are mechanisms that lead to intense energy concentration and are thought to be responsible for initiation due to mechanical stimuli. Since these processes are generally induced by shock loading, it is essential to understand the effects of high pressure on plastic deformation in molecular crystals. In this work we consider molecular crystal HMX and evaluate by atomistic simulations the effect of pressure on the Peierls stress and mobility of dislocations, with implications for the pressure dependent yield stress and strain rate sensitivity. We also report the effect of pressure on the g-surface for the most active slip planes of HMX. Implications for the continuum-scale constitutive description of plasticity are discussed.