Study of energy localization in shocked PBXs through interface-resolved reactive simulations on imaged profiles of HMX crystal aggregates

The formation of hot spots is known to be the primary mechanism for shock to detonation transition in energetic materials such as plastic-bonded explosives (PBXs). However, the mechanistic details of shock initiation are yet to be fully understood and quantified into closure models for energy localization. In recent literature, an experimental procedure was presented to observe hot spots in deconstructed PBX samples of HMX crystals embedded in a polymeric binder, dynamically compressed using laser-launched flyer plates. We present a computational framework to perform mesoscale continuum mechanics simulations for head-to-head comparison with the experimental tests. The crystal profiles were extracted from CT scan images and imported into the computational domain. The computations leveraged interface-resolved reactive simulations using a sharp-interface Eulerian framework, along with vetted reaction and strength models for HMX and binder (Estane). The study assesses the relative importance of several experimentally observed and simulated mechanisms for hot spot initiation in PBXs, such as intra-crystal void collapse, shock-focusing at surface asperities, pores in the binder, delamination zones at crystal-binder interface, and crystal-crystal interactions.