A unified viscoelastic model of progressive damage and failure for solid propellants

A general viscoelastic model incorporating the progressive damage evolution and failure criterion is developed for solid propellants across a wide range of temperatures (223 K to 333 K) and strain rates (2.38 × 10⁻⁴ /s to 4.76×10⁻²/s). (i) The progressive damage evolution, characterized by continuous void cavitation and growth, is linked to a macroscopic damage variable derived from a simple damage potential threshold, making it possible to determine the microstructural damage from experimental data. (ii) The failure criterion introduces two microstructural ingredients: the strain energy density, which accounts for both the glassy and rubbery failure of the polymer matrix, capturing brittle and ductile fracture modes at low and high temperatures respectively; and the void volume limit accounts for interface debonding, a process of particle detachment from the matrix. The implementation of the model effectively predicts the damage response and failure strains under uniaxial tension, cyclic and complex loading as well as superimposed pressure. Results reveal strong temperature/strain-rate dependency in the tensile strength, volume dilatation, and failure strains. Given that the model unifies progressive damage with ultimate failure and requires only a few model parameters, it assists in establishing a fracture criterion for the nonlinear fracture behavior of viscoelastic materials.