Interface-resolved reactive simulations of initiation through flyer impact on HMX crystal – binder aggregates

Mesoscale simulations of the shock initiation phenomena in plastic-bonded explosives (PBXs) provide inputs in a multiscale framework, specifically by developing closure models for energy localization. Validation of such models is challenging however, as direct comparison with experiments is often limited by modeling over-simplifications of the initial and boundary conditions. Here, we present a computational framework and modeling techniques aimed at pushing the envelope on capturing the physics and validating against experiments in flyer-impact induced initiation of a PBX sample. The Al flyer and the binder matrix are modeled explicitly (as distinct phases) while the HMX crystals embedded in the binder are imaged from nano-CT scans. The flyer impact on the PBX sample is simulated as it occurs in experiments, i.e. instead of modeling the impact through a shock pulse boundary condition, thus realistically representing effects of the reflected relief wave (prominent in thin-flyer experiments). All interfaces are treated as sharp entities via the ghost-fluid method for the levelsets, and techniques are developed to suppress numerical instability typical in problems involving materials with high impedance mismatch, in this case, the flyer-binder interaction. The Eulerian framework used herein also leverages higher-order schemes and local mesh refinement, yielding interface-resolved reactive calculations enabling head-to-head comparison with experiments on PBXs.