Discontinuous ablation behavior of four-directional dual-matrix C/C composites under dual-pulse solid rocket motors

Four-directional dual-matrix C/C composites were fabricated from PAN-based carbon fibers using a combined approach of soft-hard hybrid weaving preform molding, chemical vapor infiltration (CVI) of pyrolytic carbon (PyC), high pressure impregnation and carbonization of pitch-derived carbon. The ablation resistance of the composites was evaluated by testing in a dual-pulse solid rocket motor, and their ablation behavi- or was investigated. The carbon rods formed by twisting and carbonizing fiber bundles, exhibited a hexagonal cross-section, surrounded by a dense PyC “wall” structure formed during the CVI process. The linear ablation rates of the composites after pulse I and pulse II were 0.068 mm/s and 0.113 mm/s, respectively. A cellular-like PyC layer and nanowire structures were deposited on the surface of the throat convergent section during the post-combustion cooling phase, while cracks and delamination occurred on and within the divergent section. The ablation of C/C composites under these conditions was a complex multi-mechanism process, including ultra-high temperatures, high-speed gas scouring, oxygen-containing thermochemical ablation, and thermal shock. This work elucidates the ablation behaviors of C/C composites under dual-pulse conditions and provides technical guidance and a theoretical basis for designing and fabricating C/C composites for extreme ablation environments.