Finite kinematics diffuse interface mechanics coupled to solid composite propellant deflagration

Abstract

Solid Composite Propellants (SCPs) are widely employed in the field of propulsion due to their enduring chemical and mechanical stability during extended periods of storage, as well as their uncomplicated production and reliable performance. Unlike liquid propellants, solid propellants are self-supporting, meaning that that they function as structural materials as well as energetic. Consequently, it is essential to understand the mechanical behavior of SCPs during deflagration, as structural failure can have potentially catastrophic consequences. SCP failure is often associated with the formation and growth of micromechanical damage sites due to thermal and mechanical loads during burning. Thus, the ability to simulate stress propagation during the burning process is a key feature for the effective design and safe use of SCPs. The ability to evaluate failure in aged propellants and of those produced using additive manufacturing is of special interest. In this work, we present an elasticity solver coupled with a thermal phase-field model of regression of SCPs. The method implements a unique strong-form solver for finite deformation material response, featuring block structured adaptive mesh refinement techniques and a multigrid solver. Two verification results for the model are presented: first, results for an infinite plate with a pressurized hole is compared to the classical Lamé solution; second, results for a clamped plate with a hole subjected to uniaxial tension are compared to the equivalent results using the traditional finite element. In both cases, a close match is observed. Next, to test the model for the application of SCPs, tension-compression tests are used to validate the model for AP/HTPB under tension. The model is then used to determine the mechanical response of an AP/HTPB SCP during deflagration, driven both by thermal and mechanical loading, with both spherical and experimentally measured mesostructures. Overall, it is determined that the model adequately captures the stress and strain fields, indicating the model’s viability for simulations that lend insight into the interplay between mesostructure, deflagration, and mechanical damage.