Observation of Damage During Dynamic Compression of Production and Low-Defect HMX Crystals in Sylgard® Binder Using X-Ray Phase Contrast Imaging

Abstract

Polymer bonded explosives (PBX) have many applications in both the military and civilian sectors, making their safety and behavior predictability of the utmost importance. Most explosive devices are typically initiated by some external stimulus; however, initiations can also occur via localized mechanical conversion of energy during impact, called ‘hot spots’. These unintended loads can lead to crystal fracture and frictional heating, amongst other mechanisms, in the energetic crystals of a PBX. In order to visualize the behavior of these crystals, high-speed phase contrast imaging experiments were conducted using synchrotron X-ray radiation to observe the internal crack behavior of simplified PBXs subjected to low velocity impact. The PBX samples used in these experiments were composed of single production-grade and recrystallized octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) crystals embedded in a Sylgard® 184 binder doped with iron (III) oxide. We observed a clear distinction in the qualitative behavior of production-grade versus recrystallized ‘low-defect’ HMX crystals which lacked significant internal voids. Production grade crystals exhibited consistent cracking behavior in the crystals, while the recrystallized crystals exhibited debonding from the surrounding binder material and cracked much less frequently. We assert that there is a clear effect of crystal quality on the behavior of PBX, which should influence future insensitive munition formulation design choices.