Impact initiation of hexanitrostilbene

A study has been made of the initiation of hexanitrostilbene (HNS) under impact using high-speed photography at microsecond framing rates. The photographic sequences show that upon impact the layer of explosive undergoes bulk plastic flow at speeds of over 250 m s −1. Initiation occurs after this catastrophic failure of the explosive due to the fact that the adiabatic heating produced by plastic deformation is extremely localized in nature. From a comparison of the melting points, uniaxial yield stress values, flow properties, and the ignition characteristics for several organic secondary explosives, it appears that explosives with high strength values are more likely to exhibit both a rapid mechanical failure and resultant ignition during impact. Addition of polycarbonate (PC) has been found to sensitize the explosive. Strain-gauge measurements of impact of pure HNS and HNS/PC samples have shown that a sudden pressure drop occurs before ignition due to rapid failure of the test material, the latter being in agreement with the photographic observations.