Temperature-dependent microdamage and mechanical sensitization of HTPB/AP/Al composite propellant under wide temperature exposure conditions

Structural integrity and thermo-mechanical safety of solid rocket propellant grains under wide-temperature storage and service environments are critical for the reliability of defence propulsion systems. However, the multiscale pathway by which short-term wide-temperature exposure affects interfacial microdamage and further alters mechanical response probability remains insufficiently understood. In this study, the thermomechanical response, detectable molecular vibrational response, interfacial microdamage, three-dimensional defect variation, and mechanical sensitivity of an HTPB/AP/Al composite propellant were investigated from −60 to 70 °C using TMA, in situ Raman spectroscopy, in situ FTIR spectroscopy, in situ SEM-DIC, in situ Micro-CT, and impact and friction sensitivity tests. The TMA results showed continuous thermal expansion without macroscopic structural instability, with a total dimensional change of 0.8060% and an overall average coefficient of linear thermal expansion of 62.01 μm/(m·°C). Raman and FTIR spectra showed no spectroscopically detectable chemical decomposition under the short-term temperature exposure conditions, suggesting that the observed structural variation was mainly associated with physical thermomechanical effects rather than detectable chemical degradation. SEM-DIC and Micro-CT results revealed that interfacial debonding, surface cracks, high-strain regions, internal porosity, crack volume fraction, connectivity, and defect-network complexity were minimized near 20–30 °C and increased toward both low and high temperatures. Impact and friction sensitivity tests further indicated that the response probability was associated with the coupling between defect-induced hotspot susceptibility, reduced temperature margin for hotspot ignition, and temperature-dependent binder mechanical state. The highest impact and friction response probabilities were observed at 70 °C, reaching 18% and 19%, respectively. These results support a defect-informed multiscale pathway linking thermomechanical deformation incompatibility, interfacial microdamage, pore-crack network variation, and mechanical sensitization, providing an experimental basis for wide-temperature safety assessment and structural reliability design of composite solid propellants.