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

Abstract

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 behavior 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.

1. Introduction

Carbon fiber-reinforced carbon matrix (C/C) composites are renowned for their excellent thermo-mechanical properties and ablation resistance at high temperatures, making them widely used in nozzle throats of solid rocket motors[1–2]. During motor operation, the throat lining faces extremely harsh environments characterized by ultra-high temperatures and high-speed gas scouring, inevitably leading to surface ablation[3–6]. Ablation causes mass loss and structural integrity degradation, affecting the normal operation and service life of the entire thermal protection system[7–10]. Thus, the ablation process of C/C composites has become a key research focus in solid rocket motor (SRM) service. Studies have shown that C/C composite ablation involves thermochemical ablation and mechanical ablation[11–13]. Thermochemical ablation refers to material oxidation at high temperatures, while mechanical erosion refers to the spalling of carbon fibers and matrix under gas flow shear stress. Qin et al.[14] developed a multi-scale thermochemical ablation model for multidirectional C/C composites used in SRM, capturing the evolution of ablation morphologies across different scales. Li et al.[15] investigated the ablation behavior of various fiber-reinforced C/C composites under small SRM test conditions. Wang et al.[16] studied the influence of specific overload conditions in solid rocket motors on the throat ablation rate of C/C composites.

To meet the higher reliability requirements of SRM, C/C composites need improvements in both preform structure and matrix. In preform optimization, different structures like 2D[17], 3D[18–19] and 4D[20–21] have been explored, with 4D C/C composites showing greater potential[22]. Zahid et al.[23] found that 4D C/C composites exhibit superior thermal shock resistance compared to their 2D counterparts. For matrix modification, ultra-high temperature ceramics (UHTCs)-modified C/C composites can enhance ablation resistance within a certain temperature range[5,24–26], but inherent issues like low service temperature and thermal expansion mismatch limit their application in extreme SRM environments. Pyrolytic carbon (PyC) deposited by chemical vapor infiltration (CVI) can improve ablation resistance[27], but the CVI limitations make it difficult to achieve high density[28]. A pitch-derived carbon (PDC) matrix can be densified under higher pressure[29], enabling the production of higher density materials. Therefore, combining these approaches may yield C/C composites with superior ablation performance.