  Crystals of energetic materials, such as HMX, embedded in plastic binders are
the building blocks of plastic-bonded explosives. Such heterogeneous energetic
materials contain microstructural features such as sharp corners, interfaces
between crystal and binder, intra- and extra-granular voids, and other defects.
Energy localization or hotspots arise during shock interaction with the
microstructural heterogeneities, leading to the initiation of PBXs. In this
paper, high-resolution numerical simulations are performed to elucidate the
mechanistic details of shock-induced initiation in a PBX; we examine four
different mechanisms: Shock-focusing at sharp corners or edges and its
dependency on the shape of the crystal, and the strength of the applied shock;
debonding between crystal and binder interfaces; collapse of voids in the
binder located near an HMX crystal; and the collapse of voids within HMX
crystals. Insights are obtained into the relative contributions of these
mechanisms to the ignition and growth of hotspots. Understanding these
mechanisms of energy localization and their relative importance for hotspot
formation and initiation sensitivity of PBXs will aid in the design of
energetic material-driven systems with controlled sensitivity, to prevent
accidental initiation and ensure reliable performance.
