Abstract: The weak propellant layer and geometric interface near the propellant/liner bonding interface are prone to Mode I debonding and crack propagation, constituting important causes of structural failure in solid rocket motor charges. To improve the mechanical properties of the interface and the weak layer, multilevel mechanical tests have been conducted on a carbon nanotube (CNT)-reinforced “weak propellant layer–liner–bonding interface” system. Tensile tests on a hydroxyl-terminated polybutadiene (HTPB)-based simulant propellant, tensile tests on an HTPB-based liner at multiple loading rates, and Mode I peel tests on propellant/liner double cantilever sandwich beam specimens have been performed. The reinforcement mechanisms have also been investigated through scanning electron microscopy observations and an analysis based on curing reaction principles. The results have shown that, within the investigated range, 0.3 wt% hydroxylated CNTs have provided the optimal overall reinforcement of the simulant propellant, increasing its elastic modulus and tensile strength by 69% and 24%, respectively. The tensile strength and elastic modulus of the liner reinforced with 2 wt% hydroxylated CNTs have reached 209% and 342% of those of the unreinforced specimens, respectively, and have exhibited loading-rate dependence. After hydroxylated CNTs have been incorporated into the interfacial sandwich-beam specimens, the maximum load and the corresponding displacement have increased by approximately 31% and 21%, respectively. Scanning electron microscopy observations have indicated that CNTs have increased crack-growth resistance by bridging cracks and voids, improving load transfer across particle/matrix interfaces, and dissipating energy through pull-out friction. Hydroxylated CNTs have exhibited superior reinforcement performance in the investigated system, which has resulted from the synergistic effects of their geometric parameters, dispersion state, and hydroxyl-induced interfacial interactions. These findings have provided an experimental basis for the debonding-resistant design of simulant solid solid rocket motor charges propellant/liner bonding systems.

Key words: carbon nanotubes, solid propellant, liner, bonding interface, mechanical properties