Shock induced hot-spot formation and subsequent decomposition in granular, porous hexanitrostilbene explosive

Abstract

Experimental and theoretical studies on granular, porous hexanitrostilbene (HNS) explosive have yielded an increased understanding of microstructural processes occurring during initiation by shock loading. Experiments involved the planar impact of HNS specimens onto fused-silica targets. Chemical decomposition liberated gaseous products, causing the pressure in the HNS to rise. Velocity interferometry measured material velocity, hence, pressure at the fused silica/HNS interface. An analysis of this pressure excursion yields chemical decomposition history. The data are interpreted in terms of a quantitative two-temperature model which considers hot spots to be formed at pore sites as a result of the irreversible work accompanying the shock. Subsequently, decomposition completion is achieved by burn fronts which propagate radially out from each hot spot at a velocity which can be determined from the bulk decomposition rate. Analysis of the experimental data in the context of the model yields several important results: the delay times corresponding to hot-spot decomposition are shorter than expected; model calculations show about the same inferred hot-spot temperature for different initial porosities and particle sizes in HNS, shock-loaded to equal pressures, which is consistent with experimental results.