Shock initiation thresholds for projectiles with curved surfaces

Abstract

The impacts of flat-nosed rods into bare conventional high explosives tend to produce either detonations or very little discernable reaction. In contrast impacts from projectiles with curved striking surfaces, such as round-nosed rods, can produce a range of reactions, some very vigorous, as well as detonations. The current work attempts to explain this complex behaviour. The identification of a predictive threshold as corresponding to the boundary of sub-detonic reactions for low pressure impacts, rather than the boundary between no reaction and detonation, is discussed in the light of experimental results. The structure of the impact shock is explored and the existence of two sonic boundaries is explained. The linkage between the theoretical initiation threshold and one of these sonic boundaries is obtained and the implications of this threshold in terms of the proportion of the diameter of the projectile needed to cause initiation are discussed and the results illustrated using CREST, a hydrocode-based reactive-burn explosive model.