One method of hazard assessment for mass detonable solid rocket propellants consists of impacting right circular cylinders of propellant end-on into thick steel witness plates at varying impact velocities. A detonation that occurs within one shock traversal of the cylinder length is termed a prompt detonation or a shock-to-detonation transition (SDT). At lower velocities, some propellants detonate at times later than one shock transit, typically 1-5 shock transits. Because no mechanism for delayed detonation has been fully confirmed and accepted by the detonation physics community, these low-velocity detonations are referred to as unknown-to-detonation transitions (XDTs). A leading theory, however, is that prior to detonation mechanically induced damage sensitizes the material through the formation of internal porosity which provides new mechanical reaction initiation sites (hot spots) and enhanced internal burn surface. To study this phenomenology, we have developed the Coupled Damage and Reaction (CDAR) model, implemented it in the CTH shock physics code, and simulated propellant impact experiments. The CDAR model fully couples viscoelastic-viscoplastic deformation, tensile damage, porosity evolution, reaction initiation, and grain burning to model the increased reactivity of the propellant. In this paper, CDAR simulations of propellant damage in spall and Taylor impact tests are presented and compared to experiment. An XDT experiment is also simulated, and implications regarding damage mechanisms and hydrodynamic processes leading to XDT are discussed.
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