Hot-spot ignition of condensed phase energetic materials

Abstract

A micromechanics approach to hot-spot formation and growth to detonation in condensed-phase energetic materials is presented. A numerical model based on fundamental conservation principles is developed to examine the dynamic and thermodynamic processes that occur in a generalized heterogeneous, energetic material subjected to weak shock loading. The work focuses on the thermal/mechanical processes that act to transfer compression work of the shock wave into localized high-temperature ignition sites. A special interest of this research is to determine the dominant physical processes occurring at different times during hot-spot formation. Processes such as viscoplastic heating, phase change, finite rate condensed-phase decomposition, gas-phase heating, and heat transfer between the void and the condensed-phase are included in the model. Results for cyclotrimethylene trinitramine (C3H6N6O6), a common ingredient in high-energy solid rocket propellants, show that viscoplastic heating is an effective mechanism for producing high-temperature regions in the energetic material adjacent to a shock-collapsed void. Furthermore, it is shown that under certain initial conditions (pore size, shock pressure, etc.), localized heating can lead to the release of chemical energy that exceeds the energy dissipated by heat losses, and that melting and the variation of condensed-phase viscosity and yield strength can greatly affect the dynamics of pore collapse.