Modeling the Thermo‐Mechanical‐Chemical Behavior of Condensed Phase Reactive Materials

Abstract

AbstractEnergetic material condensed phase constituents come into contact, chemically react, and simultaneously undergo a phase change. Phase change in a given molecular material is often considered separately from the chemical reaction. We use a self‐consistent continuum, thermo‐mechanical model based on specified Gibbs potentials for all relevant component species that are present in a single material. A single stress tensor and a single temperature are assumed for the material.Physically‐based mass fractions of the components are used to describe composition and phase and chemical change and replace order parameters used in older phase‐field variable theories. Our formulation is entirely analogous to non‐equilibrium theories used for gas‐phase combustion but generalized to include condensed phases. We describe the formulation and illustrate its use with three examples. Example 1. considers the quasi‐static heating of an oxide‐coated aluminum particle, that is slowly heated so that the temperature within the particle can be considered a constant. We compute the stress and displacement within the particle by using the derived multicomponent equation of state. Example 2. shows how to model the melting and vaporization in a rapidly heated, confined slab of initially solid aluminum. The model treats multi‐phase transitions and illustrates how the multicomponent equation of state is used. Example 3. describes the modeling of mechanical thermo‐chemical ignition processes in a nano‐slab of HMX and considers six components: Two solid (beta and delta HMX), one liquid HMX component, and two gas components for vapor HMX and reacted products. We describe some possible next steps for further study and model improvements and how to interact with modern reactive molecular dynamics.