Multiscale viscoelastic constitutive modeling of solid propellants subjected to large deformation

This paper develops a multiscale nonlinear viscoelastic constitutive model for the Nitrate Ester Plasticized Polyether (NEPE) propellant with high elongation. The proposed model considers viscoelasticity, strain rate, confining pressure, and softening effects. The macroscopic damage due to interface debonding or failure in the matrix itself is investigated by capturing the microstructural changes in a representative volume element (RVE). To account for the evolution of interface debonding, a physics-based normalized debonding ratio is introduced and modeled using a cohesive zone model (CZM). As the damage functions are obtained from the RVE, decoupled calibration of the material parameters is possible. The model is then programmed into ABAQUS via a subroutine for numerical analysis. The effects of strain rate, multi-step relaxation, creep, and confining pressure on the stress response are presented. Overall, the predicted results are in good agreement with the experiments.