In-Situ Observation of Impact Induced Failure in HMX Single Crystals Containing Abnormal Pores Using X-ray Phase Contrast Imaging

Polymer bonded explosives combine weak ceramic crystals with polymer matrices to improve machinability and impact sensitivity. These materials are subject to a variety of loading conditions and mechanical shock during routine use that causes unknown damage to the composite. Damage is theorized to increase the potential formation of hotspots, one of the primary ignition mechanisms of PBX. During hotspot formation mechanical or electrical energy is converted into heat in localized regions, the formation and dynamics of which are controlled by local failure and energy dissipation mechanisms. Thus, understanding the material response to this damage is paramount for continued safe utilization of these materials. Here we characterize this damage during single stage gas gun impact experiments on HMX crystals contained in a Sylgard-184® polymer matrix using X-ray Phase Contrast Imaging at the Dynamic Compression Sector of the Advanced Photon Source. A Focused Ion Beam (FIB) was used to mill angular pore shapes through laboratory grown single crystalline HMX. These pore shapes better mimic flaws found in organically grown crystals while maintaining lab scale control over size, shape, and location. As a result, characterizing HMX behavior during failure both experimentally and computationally is simplified. Increased knowledge of the deformation mechanisms in HMX supports a better understanding of subsequent failure dynamics and leads to safer and more appropriate application and use.