Hotspot formation in polymer-bonded energetic materials by large scale atomistic simulations*

Polymer-bonded explosives (PBXs) are particle composites with a high concentration of energetic material and a few percentage of polymer binder. The hotspot formation mechanism of PBXs under shock conditions is still not clear due to their complicated microstructure and the extreme difficulties in the characterization of defect distribution. In contrast to the costly experiments, computational simulations provide a valuable tool for revealing the hotspot formation mechanism. In this study, we conducted large scale molecular dynamics simulations on a three-dimensional PBX system, which was created by an in-house PBX builder, with a composition of 90% RDX particles and 10% PS chains and a system size of 10 million atoms. The RDX particle size distribution is assumed to be following a bimodal distribution and the packing fraction is about 0.65. We performed a double-shock deformation on the PBX system to get temperature field. The microstructures, such as void distribution etc., were computationally characterized and their relationship with hotspot distribution are established. Most importantly, we developed a pathway to separate the hotspots due to void collapse from those due to interface frictions.