Due to the complex service environment of solid rocket motors, solid propellants are subjected to varying temperature and strain rate loads during storage and flight operations, exhibiting complex failure behaviors. To address the current lack of understanding regarding the damage mechanisms of solid propellants under coupled thermomechanical loading, this study improved an in-situ testing instrument, enabling integration with multiple mesoscopic imaging systems. In-situ mechanical experiments were performed across a wide temperature range (238 K to 343 K) and strain rate range (0.00024 s −1 to 0.12 s −1 ), capturing the mechanical response characteristics of the propellant at both macroscopic and mesoscopic scales. Based on the macroscopic stress response, damage variables that evolve dynamically with loading were extracted and incorporated into a newly developed nonlinear rate-thermal viscoelastic constitutive model. Comparison with experimental results demonstrates that the model can effectively predict the stress-strain behavior and damage evolution process of the propellant under diverse operational conditions. Furthermore, by integrating in-situ observations of mesoscopic damage phenomena, including matrix fibrillation, particle/matrix interfacial debonding, and void nucleation, growth, and coalescence, the dependence of damage characteristics on external loading conditions was systematically elucidated. Finally, an innovative cross-scale damage evolution pathway was established, which links microscopic molecular mechanisms, mesoscopic structural responses, and macroscopic mechanical behavior, thereby clarifying the influence of temperature and strain rate on the damage mechanism from a multi-scale perspective. This work provides a robust theoretical foundation and technical support for enhancing the mechanical performance and structural integrity of solid rocket motors. • Temperature/strain rate-dependent mechanical behavior of propellant is obtained. • A nonlinear rate-thermal viscoelastic constitutive model is developed. • Multi-dimensional damage evolution is observed and analyzed using in-situ technique. • Mesoscopic damage mechanisms under thermomechanical are revealed by in-situ SEM. • A cross-scale damage pathway is established for NEPE propellant.
Yang et al. (Sun,) studied this question.