Hot Spot Ignition and Growth in Shock-Induced RDX through MD-informed Void Collapse Simulations*

Continuum-scale shock-induced void collapse resulting in hot spot evolution is a crucial mechanism for determining shock sensitivity of energetic materials. Hot spots, i.e., localized areas of high temperature. arise from a shock interacting with internal defects within the microstructure. The ignition and growth of hotspots in a shocked energetic material can contribute to rapid chemical reactions within the material, potentially leading to a self-sustained detonation wave. In this work,  void collapse calculations were performed using 1,3,5-Trinitro-1,3,5-triazinane (RDX) as the energetic material. A circular void embedded into the center of a block of RDX is exposed to a reverse ballistic shock, where varying shock velocities were explored. The computational setup for the continuum and molecular scale simulations are nearly identical. The material models used for the calculations are derived from molecular dynamics data and take the form of a third order Birch-Murnaghan equation of state, rate-dependent Johnson Cook strength model, pressure-dependent melting temperatures and chemical reaction rates. The ensuing void collapse and hot spot behavior is then compared to physically identical coarse grain and atomistic simulations. The overall goal of this work is to establish material models to perform physically accurate simulations, to enhance understanding of hot spot formation in RDX and ultimately use continuum-scale hot spot data to inform macro-scale shock simulations.