Nonlinear Creep Constitutive Model and Its Finite Element Implementation for Composite Solid Propellant with Aging and Damage

Abstract

Assessing the long-term structural integrity of solid rocket motors during storage requires a thorough understanding of the complicated creep behavior of composite solid propellants, particularly the effects of material aging and damage progression. This paper systematically investigates the creep behavior of composite solid propellants considering the coupling effect of aging and damage. The objective is to establish a nonlinear creep constitutive model that can describe the entire creep process of composite solid propellants and to explore its implementation in finite element analysis. Firstly, crosslink density is used to characterize the aging process of the propellant, and a modified cumulative damage model is proposed to construct a nonlinear creep constitutive model that includes the coupling effect of aging and damage. In the experimental section, the basic principle to determine the crosslink density of the propellant using the swelling method is introduced, and model parameters are obtained from experimental data. Subsequently, a method is proposed to obtain the parameters of the damage evolution model through creep fracture experiments, and the accuracy of the proposed creep constitutive model is validated. Finally, based on the Abaqus finite element software, the finite element application of the constitutive model is implemented via the CREEP subroutine, and its effectiveness in propellant creep analysis is verified. The results indicate that the established constitutive model can effectively describe the creep process of composite solid propellants under different stress conditions, considering both aging effect and damage evolution. In engineering applications, this study provides important theoretical support for the analysis of aging, damage, and creep deformation of propellant grains in solid rocket motors under long-term storage conditions.