In order to delve into the fatigue life distribution of solid rocket motor charge structures under vibration loads, equivalent vibration loading conditions for numerical analysis were hereby established based on measured transportation vibration load spectra. The fatigue life of hydroxyl-terminated polybutadiene (HTPB) charge under various working conditions was measured through fatigue cyclic loading tests, and a fatigue life model was correspondingly constructed. Subsequently, numerical simulations were conducted using the UMAT secondary development technology and a three-dimensional finite element model of the solid rocket motor. Building on these simulation results, the fatigue life distribution characteristics of the charge were then analyzed. As indicated by the study findings, under vibration loads, the overall fatigue life of the motor charge gradually decreases with increasing loading cycles and vibration amplitude. The regions of significant fatigue life decline initially emerge at the root of the charge’s star-shaped holes, subsequently propagating to the inner walls of the charge, and eventually to the outer surfaces of the charge. From the perspective of the fatigue life of the charge structure as a whole, the parts with small fatigue life, i.e., the danger zones, are mainly distributed in the star-shaped holes of the charge and in the part of the area where the outer surface of the charge is bonded to the liner. These areas necessitate special attention.

In this study, we explored the evolution of mechanical properties in hydroxyl-terminated polybutadiene (HTPB) propellants under fatigue loading by performing fatigue tests with varying maximum stresses and cycle numbers, followed by uniaxial tensile tests on post-fatigue specimens. Residual elongation was used as a key parameter to characterize mechanical behavior, while scanning electron microscopy (SEM) provided insights into the mesostructural morphological changes that occur under different loading conditions, revealing the mechanisms responsible for variations in mechanical properties. The results show that, as the number of loading cycles increases, residual elongation decreases, with three distinct phases of decline—slow change, gradual decline, and rapid deterioration—depending on the stress levels. SEM analysis identified damage mechanisms such as “dewetting” and particle fragmentation at the mesostructural level, which compromise the material’s structural integrity, leading to reduced residual elongation. A novel aspect of this study is the application of Williams–Landel–Ferry (WLF) theory to construct a master curve describing residual elongation decay. This approach enabled the development of a generalized model to predict the material’s degradation under fatigue loading, with experimental validation of the fitted evolution model, offering a new and effective method for assessing the long-term performance of HTPB propellants.