Numerical modeling of shock-to-detonation transition in energetic materials

Determining the hazard classification of energetic materials is important for transportation safety and storage concerns. To avoid costly grain redesign and additional testing, a model that adequately predicts the shock sensitivity of energetic materials is required, particularly the outcome of the Naval Ordnance Laboratory Large Scale Gap Test. The goals of this effort are to develop and validate computational tools that predict the shock sensitivity of energetic materials. Specifically, to use our packing code, Rocpack, to generate morphologies of interest for shock sensitivity assessments, and to use our CFD code, RocSDT, to propagate shocks of various strengths through the pack to predict the onset of detonation.Dealing accurately with the material interfaces in this problem is a long-standing challenge, as familiar strategies lead to spurious temperature spikes, and therefore spurious reaction rate spikes. We describe a new strategy, which does not generate spurious spikes, and demonstrate via a number of test problems that numerical convergence can be achieved. We also examine two problems that are stepping stones to a complete simulation; both are planar. In the first, we consider the passage of a shock wave through pure HMX in which a line of hot spots of the kind generated by void collapse are located a short distance behind the shock. When the hot spot spacing is large, the shock remains a shock; when small, transition to detonation occurs. In the second problem we also insert hot spots, but into a matrix of HMX particles and binder.