A constitutive model of the solid propellants considering the interface strength and dewetting

The solid propellant as a typical viscoelastic composite, consists of oxidizer particles, fuel particles, and polymeric binders. After experiencing the service conditions under complex stress states and temperature cycles, solid propellants would be damaged by the interface dissociation between polymeric binders and oxidizer particles, termed dewetting. The dewetting behaviors would cause combustion instability of solid propellants, and might lead to failure of the rocket motor. To evaluate the health of solid propellants, we introduced a parameter of the normalized crack length to describe the interface dissociation, and developed a physics-based constitutive model. To predict the thermal-mechanical response of solid propellants under complex loading conditions, this model considers the interface strength, the volume relaxation of voids, and the viscoelasticity of polymeric binders. We programmed this model into the finite element software, validated the model by comparing with the experiments, and analyzed the responses at various loading conditions. Towards applications, we modeled the dumbbell-shaped samples in tensile tests and the cylindrical grain under impact loading, and analyzed the damage field. Overall, the developed model can be used to predict the thermal-mechanical responses of solid propellants in the structure level, and to evaluate the state of a solid rocket motor under service.