Getting continuum hotspot temperatures of β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (β-HMX) in agreement with atomistics

The initiation of detonation in shocked energetic materials often involves the formation of hotspots resulting from pore collapse. These hotspots are crucial as they lead to localized energy concentration in the vicinity of the pore collapse, triggering chemical reactions. Since reaction rates are highly dependent on temperature, it is crucial for predictive continuum models to accurately represent the dynamics of pore collapse, especially the temperatures of the hotspots. Achieving this level of precision places strict demands on the accuracy of thermophysical model formulations and parameters. In this study, we focus on material models for β-HMX in the context of continuum pore-collapse simulations, with molecular dynamics (MD) calculations as the benchmark. By employing material properties consistent with MD, we demonstrate that the currently available strength models for HMX do not effectively capture pore collapse and hotspot temperatures. Drawing insights from MD, we introduce modifications to a Johnson-Cook strength model, specifically focusing on the material's response to shear strain and strain rate. We show that this refined strength model for β-HMX closely matches MD-predicted results across various aspects, including pore collapse rate, the mode of pore collapse, the formation of shear bands around the pore, and the temperature distribution within the hotspot surrounding the pore.