Improving the model fidelity for the mechanical response in a thermal cookoff of HMX

Understanding the response of energetic materials to adverse thermal environments is necessary to have confidence in the safety of those systems. In the past few years we have been improving our thermal-mechanical-chemical modeling of HMX/Viton-A based systems. Time to event predictions are very good, to within a degree of the experimental result. However, the chemical network/reaction rates are under constrained, and many networks can achieve the same level of accuracy. Recently, we have significantly improved the mechanical response modeling by the inclusion of porosity and surface tension in the solid species in the reaction network. Here we consider the effect of HMX sublimation on the reaction network, and also consider the effect of the trapped gas in the ullage space on the overall mechanical response of the models of experiments like the Scaled Thermal Explosion eXperiemt.