Damage Evolution Mechanism, Accelerated Aging Model Framework, and Failure Lifespan Prediction of <scp>HTPB</scp> Propellants Under Thermomechanical Coupling

ABSTRACT This study explores the aging behavior of hydroxyl‐terminated polybutadiene (HTPB) propellants under thermomechanical coupled conditions through combined macroscopic mechanical testing and mesoscopic structural characterization. A critical maximum stress level threshold (in our condition: σ Max ≈ 0.14 MPa) is identified, beyond which the damage mechanism shifts from localized microcracking to large‐scale structural failure, significantly accelerating performance degradation. Experimental results reveal that HTPB propellants exhibit cumulative damage and synergistic failure under combined thermal cycling and alternating loading. A “maximum stress–cycle ratio” main curve model and corresponding shift factor model are developed based on strength retention data. These models form the basis of an accelerated aging model framework. Their physical implications were interpreted using established theoretical frameworks. Additionally, mesoscopic porosity was introduced as a key damage metric, supporting the development of a quantifiable multi‐scale aging failure criterion. A transformation relationship between equivalent cycle ratio and actual service time was also established. Using this framework, the aging failure life of HTPB propellants was estimated at approximately 18.03 years under typical service conditions.