Modeling the effect of voids on solid composite propellant deflagration and mechanics

Abstract

Voids can form within solid composite propellants (SCPs) during various stages of production and use, altering burn characteristics and subsurface mechanical response. This can be hazardous because the actual burn rate may be different from predicted values (altering the thrust profile and reducing controllability) and because the stresses may exceed nominal values (leading to damage or fracture). This work presents a stabilized phase-field formulation for simulating SCP deflagration in void-containing mesostructures. The formulation extends a previously developed full-feedback regression model by introducing a temperature-cutoff mobility that suppresses subcritical interface motion, preventing nonreacting void surfaces from evolving due to curvature-driven artifacts while preserving high-temperature regression behavior. The stabilized model is applied to ammonium perchlorate (AP) / hydroxyl-terminated polybutadiene (HTPB) mesostructures with AP sizes between 2.5 μm and 15.0 μm at 1 MPa and 7 MPa gauge pressures, with and without voids inside AP particles. The simulations predict regions of maximum temperature, fluctuations in instantaneous burn rate, and stress fields induced by nonuniform thermal expansion and pressure loading during regression. Predicted regression rates agree with experimental data within 28% error for all geometries at 1 MPa, while high-pressure results capture relevant trends but indicate the need for additional gas-phase or radiative heat-transfer physics. These results provide a physics-based framework for investigating how void morphology alters SCP regression and subsurface mechanical response.