Three-dimensional simulations of pore collapse: comparison of atomistic and continuum calculations

Shock-induced collapse of 3D pores of micro (nanometer) scale and various shapes embedded in the energetic crystal RDX (1,3,5-trinitro-1,3,5-triazinane) is examined using all-atom molecular dynamics (MD) and atomistics-consistent continuum models. The continuum simulation employed MD-derived material models, including a recently advanced Modified Johnson-Cook (M-JC) strength model for RDX. Shear band formation, pore collapse rate, hotspots patterns for 3D spherical pore collapse under various loading strengths are compared head-to-head between continuum and MD under almost identical boundary and impact conditions. Scale invariance of pore collapse and hotspots are also investigated for collapse of pore with the same setup but for larger pores that are not accessible in 3D atomistic calculations. This study enhances confidence in recently developed MD-consistent continuum model for RDX, for which agreement with MD was seen in earlier 2D work. Additionally, collapse of 3D elongated shaped pores (ellipsoids) under various impact strength and orientation is studied using continuum mechanics. The formation of shear band patterns and vortical structures, as well as hotspot metrics are analyzed, providing insight into physics of their collapse, which is important in predicting shock to detonation transition of real RDX microstructures containing pores and defects.