Solid propellants are particulate composite with a light cross-linked elastomeric binder filled with a high concentration of energetic, solid aggregates. Solid propellants are often considered as highly nonlinear elastomeric materials, with elastic behavior resulted from its binder and plastic behavior from its energetic particles. The study of the micro-structure and mechanical properties of solid propellant is crucial for its design, safety evaluation, and lifetime prediction of solid fuel carriers. The constitutive model proposed for rubber-like material can often be generalized to predict the nonlinear behavior of solid propellant due to the dependency on the mechanical behavior of solid propellant on its elastomeric binder material. This paper focuses on developing a model that predicts the stress softening and strain-residual mechanism of the solid propellant. This micro-mechanical model for solid propellant was proposed based on the network evolution theory. The motivation of this study is the lack of a micro-mechanical model that can describe both the stress softening effect and strain residual in the quasi-static behavior of propellants. The simplified network-evolution model with only five parameters is a simple micro-mechanical model that captures both the stress softening effect and strain residual. Besides the simplicity and reduced fitting procedure, the model was validated against several experimental data and illustrated good agreement in small and large deformations, making the proposed model a suitable option for commercial and other applications.

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