Void collapse simulations using a molecular-dynamics-informed rate-dependent elastoplastic model for HMX

A predictive computational model for detonation initiation in EMs must encapsulate physical mechanisms across length-scales ranging from molecular through microstructural to macroscale. A Molecular Dynamics model (MD) or an anisotropic rate-dependent crystal plasticity model may be able to capture mechanisms of energy localization at the different length scales. However, these models are computationally expensive and impractical for real-life problems. Isotropic rate-independent strength models are popular; however, they miss important physics (e.g. rate-dependent features such as shear localization). In this work, an MD informed rate-dependent J2-plasticity model is developed that captures the salient mechanism of energy localization in HMX. The model produces results in agreement with MD calculations for 1D shock passage through an HMX block, and for cylindrical pore collapse in HMX. It also performs well under a wide range of strain rates. It is shown that an MD-calibrated isotropic rate-dependent strength model produces similar results as MD calculations but at a much lower computational cost. This makes it feasible to predict the detonation-initiation of practical-size explosive samples of HMX.