Microdamage Evolution and Combustion Enhancement of a High-Energy Composite Propellant under Thermal Cycling

Thermal cycling is a critical environmental factor affecting the combustion behavior of high-energy composite propellants. In this work, the effects of thermal cycling (−60 to 70 °C) on microstructure evolution, gas transport, ignition characteristics, flame structure, and burning rate of a NEPE-type high-energy composite propellant were systematically investigated. Results show that thermal cycling induces progressive interfacial debonding and microcrack formation, leading to the development of a weakly connected pore network. Although no new decomposition pathways are observed, headspace FTIR/MS analysis shows enhanced low-temperature gas migration, with selected MS signals increasing by up to 55%. TG-FTIR further reveals more pronounced enhancement of characteristic gas-release intensities during active thermal decomposition. High-speed imaging results indicate that ignition delay decreases from 368.2 ms to 32.1 ms with increasing cycle number. The maximum flame area increases by 77.0%, and peak flame length increases by 54.4%. The burning rate at 1 MPa increases from 0.82 to 2.44 mm/s. Pressure-dependent combustion tests further show that the burning rate at 5 MPa increases from 3.45 to 10.20 mm/s, while the pressure exponent increases from 0.82 to 0.96, indicating enhanced burning intensity and pressure sensitivity after thermal cycling. Flame emission spectroscopy indicates intensified gas-phase reactions, with OH*, CN*, and AlO emission intensities increasing by 22%, 38%, and 55%, respectively. Post-combustion residue analysis reveals enhanced aluminum oxidation and agglomeration behavior. Overall, thermal cycling does not change the primary decomposition pathway but significantly enhances combustion through a microdamage-driven gas transport and flame feedback mechanism.