In order to reveal the aging mechanism of solid propellant grain during the long-term storage, a HTPB (hydroxyl-terminated polybutadiene) propellant rocket motor which was moulded by casting and stored naturally for 19 years was dissected. Samples were taken along the radial position of the propellant grains, and were tested and analyzed by means of SEM (scanning electron microscope), EDX (energy dispersive X-ray spectrometer), infrared absorption spectroscopy and cross-linking density. Results show that the aging degree of propellant is not the same at different positions of grain. The closer the position is to the non-metallic case, the more serious the aging degree of propellant is. Further analysis shows that, in addition to the effects of C=C double bond oxidation chain breaking and condensation of -OH on propellant aging, Al³⁺ ions produced by the oxidation of Al powder catalyzes the addition reaction of HTPB′s C=C double bond with Cl₂ or water to form C=Cl double bond and secondary alcohol, and the uneven migration and distribution of aluminum ions will cause the uneven aging of grain. The research results are of great significance to the improvement of propellant aging performance and the research of anti-aging measures.

Tensile and compressive creep behavior of propellants in solid motors due to the influence of the gravity and long-term storage might affect the interior ballistics and structural integrity. In order to investigate the change trends of tensile and compressive creep for HTPB propellant, the 1000 s tensile, 1000 s compression and 28 d tensile creep tests were designed and carried out in this work. Meanwhile, the Saint-Venant body and the compressive-tensile asymmetry factor were introduced to establish a propellant viscoelastic plastic constitutive model that takes into account compressive-tensile asymmetry. The range of application of this equation was obtained by fitting and analyzing the parameters in the constitutive equation. The results indicate that the compressive creep process of propellant was mainly dependent on stress level. At the same stress level, viscoelastic deformation of tensile creep is about 1.62 times that of compressive creep, while compressive yield stress is 3.82 times that of tensile yield stress. The tension-compression asymmetric viscoelastic plastic constitutive model can well characterize the tensile-compression creep response of propellants at the lower stress levels. The conclusions and research method in this work can provide reference for structural integrity analysis and storage life evaluation of solid motor.