Key Takeaways & Executive Findings
- •• • Linear ablation rates of 0.068 mm/s (pulse I) and 0.113 mm/s (pulse II) demonstrate a 66% increase in ablation rate under dual-pulse conditions, indicating cumulative damage that must be accounted for in thermal protection design. • • The formation of a cellular-like PyC layer and carbon nanowires in the convergent section, catalyzed by ferrocene derivatives, reveals a deposition mechanism that can mitigate ablation but requires controlled pyrolysis conditions. • • Debonding at matrix-fiber, carbon rod-PyC, and within the PDC matrix interfaces led to crack initiation and delamination in the divergent section, highlighting the need for improved interfacial bonding to prevent mechanical erosion. • • The ablation process is characterized as discontinuous, involving high-temperature/high-velocity gas erosion, thermochemical ablation by oxygen-containing species, and thermal shock, necessitating multi-mechanism modeling for accurate lifetime prediction.
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), and high-pressure impregnation and carbonization of pitch-derived carbon. The ablation resistance was evaluated in a dual-pulse solid rocket motor, and the 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. The linear ablation rates 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 process involved ultra-high temperatures, high-speed gas scouring, oxygen-containing thermochemical ablation, and thermal shock. This work elucidates the ablation behaviors under dual-pulse conditions and provides technical guidance for designing C/C composites for extreme environments.
1. Introduction
Carbon fiber-reinforced carbon matrix (C/C) composites are critical for nozzle throats in solid rocket motors (SRMs) due to their exceptional thermomechanical properties and ablation resistance. However, during motor operation, the throat lining faces ultra-high temperatures and high-speed gas scouring, leading to surface ablation that degrades structural integrity and limits service life. Traditional single-pulse SRM tests do not capture the cumulative effects of multiple ignition pulses, which are increasingly relevant for advanced propulsion systems requiring throttling and restart capabilities.
This study addresses the gap by evaluating four-directional dual-matrix (4D-DM) C/C composites under dual-pulse solid rocket motor (DPSRM) conditions. The composites, fabricated via hybrid weaving and combined CVI and high-pressure impregnation carbonization, exhibit a unique microstructure with hexagonal carbon rods surrounded by PyC walls. The dual-pulse testing reveals discontinuous ablation behavior, with a significant increase in linear ablation rate from 0.068 mm/s after pulse I to 0.113 mm/s after pulse II. This work provides critical insights into the multi-mechanism ablation processes and microstructural evolution, offering a theoretical basis for designing C/C composites for extreme, multi-pulse environments.
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Wei Lianfeng, Wang Running, Zhang Jiaping, Li Kezhi, Cui Hong (2026). Discontinuous ablation behavior of four-directional dual-matrix C/C composites under dual-pulse solid rocket motors. New Carbon Materials. https://doi.org/10.1016/S1872-5805(26)61069-4
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Frequently Asked Questions
What are the specific linear ablation rates after each pulse and what does the increase indicate?
The linear ablation rates were 0.068 mm/s after pulse I and 0.113 mm/s after pulse II. The 66% increase indicates that cumulative damage from the first pulse, such as microcracks and increased surface roughness, accelerates ablation during the second pulse. This necessitates designing thermal protection systems with safety margins for multi-pulse operations.
How does the microstructure of the 4D-DM C/C composite influence its ablation behavior?
The hexagonal carbon rods surrounded by dense PyC walls create a dual-matrix structure that initially provides good ablation resistance. However, during ablation, debonding occurs at multiple interfaces (matrix-fiber, carbon rod-PyC, and within the pitch-derived carbon matrix), leading to crack initiation and delamination, especially in the divergent section. This suggests that interfacial bonding is a critical factor for improving durability.
What mechanisms are responsible for the deposition of PyC and carbon nanowires in the convergent section?
PyC deposition results from pyrolysis of the motor's insulation layer after propellant combustion, while carbon nanowires form via catalytic reactions involving ferrocene derivatives that migrate from the propellant to the insulation layer and liner during pyrolysis. These deposits may act as a protective layer, but their formation depends on specific temperature and gas composition conditions.
How does the ablation behavior under dual-pulse conditions differ from single-pulse conditions?
Under dual-pulse conditions, the ablation is discontinuous, with the first pulse causing initial damage and the second pulse exacerbating it. The linear ablation rate increases significantly, and post-test analysis reveals more extensive cracking and delamination. This highlights the need for testing under realistic mission profiles to capture cumulative effects.
What are the implications of this study for the design of C/C composites for extreme ablation environments?
The study provides a theoretical basis for optimizing the microstructure of C/C composites, such as enhancing interfacial bonding and controlling PyC deposition, to improve ablation resistance under multi-pulse conditions. The findings also emphasize the importance of considering multiple ablation mechanisms—thermochemical, mechanical, and thermal shock—in material selection and design.
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