A viscoelastic constitutive model considering deformation and environmental-induced damages for solid propellants

Realistically representing the constitutive response of solid propellants is crucial for industrial use and service life assessment of solid rocket motors (SRMs), as they are generally stored for a long time and exposed to complex loadings and environmental conditions, resulting in the possible loss of the grain structural integrity of SRMs and consequently the failure in the motor. This contribution develops a three-dimensional viscoelastic constitutive model that considers the effects of damages caused by environmental factors and large deformation. Environmental-induced damages are represented by introducing normalized crosslinking density (CLD) and micropore evolution, which is assumed to be the coupled results of oxidation, hydrolysis, degradation, migration, etc. Deformation-induced damages are attributed to interface debonding or failure in the binder as well as cyclic loadings. An ABAQUS subroutine based on the current model is then applied for numerical analysis. The effects of strain rate, temperature, confining pressure, cyclic loadings, and environmental aging on the stress response are presented. The predicted results match reasonably well the experiments. As the model takes into account the microstructural changes both due to mechanical loadings and environmental effects, it applies to the stress analysis of solid rocket motors, whether new or stored for years.