Effect of Loading Wave Profile on Hydrodynamic Void Collapse in Detonation Initiation

Abstract

We experimentally and numerically investigate void collapse as a mechanism for detonation initiation in porous energetic materials under a stress-wave loading condition, representative of accidental mechanical insult. In contrast to the step loading of a shock, a stress wave induces a ramp loading, where length scales of the wave may be comparable to the void size. Using an inert and transparent polymer material, we decouple the reactive and material aspects of void collapse, and focus instead on the hydrodynamic process of interactive void collapse. Diagnostic techniques include high speed shadowgraph movies of the collapsing voids and particle image velocimetry in the surrounding material. Two dimensional finite volume simulations compare the interaction of a single void undergoing ramp and shock wave loading. Voids exhibit asymmetric collapse, with formation of a high speed jet that originates from proximal wall of the void. Data obtained, including internal volume histories and collapse times of current experiments and simulations, are reported and compared with shock-induced cavity collapse data from the literature.