Solid Propellant Micro-scale Failure Mechanisms and Their Influence on Progressive Damage Propagation and Accumulation

The research deals with the structural behavior, integrity and response till failure of solid propellants under different loadings. Solid propellant is composed of small solid particles embedded in a binder; therefore, the investigation required the response study on a micro-scale level associated with damage initiation, it’s progressive development and accumulation. Macro-scale level response till failure in presence of the micro-scale damage initiated and developed in the propellant was studied.

A micro-scale random Representative Unit Cell (RUC) of solid propellant internal structure was developed and implemented. A rectangular and a cylindrical sector RUC models were studied. Spherical solid particles of different sizes and materials embedded in a rubber binder were modeled. A nonlinear hyperelastic material model for the binder was adopted to allow micro- and macro-scale high strains. A bilinear mixed mode cohesive contact model was adopted for the particle-binder interface and interface failure mechanism. Micro-scale level failure of the particle-binder interface and binder failure were detected under applied loads. Parametric study of different cohesive material parameters and geometry parameters was conducted. Random particles distribution and particles size influence was studied and found to impact macro-scale behavior. Macro-scale stress strain relations under cyclic loading show strong effect of micro-scale damage initiation and accumulation. Mullins like effect under cyclic loads was observed. The research performed demonstrated the failure process of the propellant, starting with local failure in the micro scale level which leds to the failure on macro scale level. The presented results were analyzed with ANSYS and LS DYNA FE packages.