Chemo-mechanically coupled damage in NEPE propellants during long-term storage: Multiscale characterization, cross-scale modeling, and structural integrity assessment

Nitrate-ester-plasticized polyether (NEPE) propellants are highly filled energetic polymer composites whose long-term storage reliability is governed jointly by microscale chemical aging, mesoscale particle-matrix interfacial damage, and macroscale viscoelastic failure. In contrast to damage driven solely by aging or mechanical loading, nitrate ester decomposition, stabilizer depletion, and binder-network evolution alter matrix viscoelasticity, interfacial adhesion, and local damage susceptibility. Under self-weight, residual stresses, and temperature fluctuations, particle-matrix dewetting, void growth, and microcrack coalescence may further evolve into a positive-feedback degradation pathway. This review critically examines the structural characteristics and degradation mechanisms of NEPE propellants, multiscale characterization techniques, macro-/meso-/microscale simulation methods, and cross-scale parameter-transfer strategies for long-term chemo-mechanically coupled damage. Particular attention is given to the correlation pathway linking microscopic chemical state variables, mesoscale damage descriptors, and macroscopic structural integrity. Current studies still face several limitations, including insufficient in situ quantitative characterization under coupled fields, inconsistent physical meanings of cross-scale parameters, empirically dominated model inversion, and incomplete engineering failure criteria. Future research should develop closed-loop predictive frameworks centered on measurable state variables and constrained by multi-source experimental data and physically consistent parameter inversion, thereby establishing the mechanistic and data basis required for future service-life prediction and structural-integrity assessment of solid rocket motors.