Initiation mechanisms in single crystal explosives: Dislocations, elastic limits, and initiation thresholds

For many years it has been thought that dislocations play a role in shock initiation of detonation in crystalline molecular explosives. Proposed mechanisms have included dislocation pile-ups causing hot-spots, or a lack of dislocation slip-systems leading to molecular entanglement and conformation change, facilitating decomposition. Previously reported results in PETN favored the steric hindrance entanglement mechanism, and HMX elastic-plastic experiments seemed to follow. More recent experiments in RDX added some uncertainty. Gas gun impact experiments were performed to resolve wave profile behavior in the regime of the beginning of shock initiation for HMX. A relatively isotropic shock initiation threshold is observed for HMX. Taken as a whole, the results to date for PETN, RDX, and HMX defy efforts to generalize initiation mechanisms. It is clear that experiments to elucidate the actual processes in these materials dynamically will be required to advance the understanding of initiation mechanisms.