  Numerous crystal- and microstructural-level mechanisms are at play in the
formation of hotspots, which are known to govern high explosive initiation
behavior. Most of these mechanisms, including pore collapse, interfacial
friction, and shear banding, involve both compressive and shear work done
within the material and have thus far remained difficult to separate. We assess
hotspots formed at shocked crystal-crystal interfaces using quasi-1D molecular
dynamics simulations that isolate effects due to compression and shear. Two
high explosive materials are considered (TATB and PETN) that exhibit distinctly
different levels of molecular conformational flexibility and crystal packing
anisotropy. Temperature and intra-molecular strain energy localization in the
hotspot is assessed through parametric variation of the crystal orientation and
two velocity components that respectively modulate compression and shear work.
The resulting hotspots are found to be highly localized to a region within 5-20
nm of the crystal-crystal interface. Compressive work plays a considerably
larger role in localizing temperature and intra-molecular strain energy for
both materials and all crystal orientations considered. Shear induces a
moderate increase in energy localization relative to unsheared cases only for
relatively weak compressive shock pressures of approximately 10 GPa. These
results help isolate and rank the relative importance of hotspot generation
mechanisms and are anticipated to guide the treatment of crystal-crystal
interfaces in coarse-grained models of polycrystalline high explosive
materials.

Materials Science;Chemical Physics