Computing relative explosive shock sensitivity from phase-space thermodynamics.

Several factors affect the shock initiation sensitivity of heterogeneous high explosives. The most widely discussed are porosity/density and initial temperature. As the process is chemical in nature, the factors that control shock-induced thermalization also play an important role, including the equation-of-state of the bulk material, and the plastic deformation that occurs within the microstructure. Thermalization drives the chemistry in a way that we describe semi-quantitatively using a heat and mass transfer approach, indicating thermal conductivity and heat capacity play a role. The chemical kinetics are clearly important, as described by the non-linear temperature-dependent reaction rate. Here, we use a hydrodynamic reaction model to compute the shock sensitivity of a specific explosive, using its physio-chemical properties and the known shock initiation response of a reference explosive. We use the Arrhenius rate form and compute the kinetic parameters using a thermodynamic approach that rests on the knowledge that sublimation of the parent molecule from the solid crystal controls the rate. That rate in turn depends on the thermodynamics of that process, determined directly from a static phase diagram. In this study, we computed the shock initiation response of the explosive PBX 9502, using PBX 9501 as a reference. We found that the problem was underdetermined, but we found the overall relative description of the two explosives and their relative hydrodynamic reaction rates to be internally consistent. [ABSTRACT FROM AUTHOR]