Role of dynamical compressive and shear loading on hotspot criticality in RDX via reactive molecular dynamics

Abstract

Energy localization in hotspots due to shock-induced pore collapse is thought to be a critical process in the initiation of heterogeneous high-energy density materials. The dynamical collapse of porosity involves expansion, jetting, shearing, and recompression of the material surrounding the defect. While the resulting hotspots are known to result in deflagration waves that can lead to detonation, we lack the understanding of the relative potency of the various processes that occur during the collapse. We use molecular dynamics simulations with the reactive force field ReaxFF to characterize how uniaxial expansion/recompression, shear, and combinations thereof affect the formation and criticality of hotspots in RDX, 1,3,5-trinitro-1,3,5-triazine. We chose a planar pore configuration consisting of a 40 nm gap and independently control the relative amounts of compressive and shear shock loadings. We find that shear-dominated critical hotspots tend to be smaller but exhibit higher temperatures than uniaxial ones and involve longer reaction time scales. Interestingly, the chemical decomposition mechanisms are affected by the relative amount of dynamical shear and uniaxial loads.