Ablation Behavior and Microstructure Evolution of Quartz Fiber Reinforced Phenolic Resin Composites Under Supersonic Ultra‐High Gradient Heat Fluxes

ABSTRACT Quartz fiber reinforced phenolic resin composites (QFPRCs) are promising candidates for thermal protection systems (TPS) in hypersonic vehicles. Hypersonic vehicles are exposed to ultra‐high and spatially non‐uniform heat flux in service. In this paper, a supersonic oxygen‐kerosene rocket engine was employed to investigate the ablation behavior and microstructure evolution of QFPRCs under supersonic ultra‐high gradient heat fluxes. It was found that as the heat flux increased from 3000 to 6000 kW/m ² , the surface of the specimen exhibited matrix consumption and SiO ₂ layer formation. High‐enthalpy jets penetrate the subsurface and advance the ablation front. The mass ablation rate rises from 0.127 to 0.163 g/s. The linear ablation rate increases from 0.042 to 0.288 mm/s, showing an exponential relationship. A fundamental transition in the ablation mechanism is presented. Below 5000 kW/m ² , oxidative melting protection dominates. Above 5000 kW/m ² , fiber decomposition and volatilization are the main processes. At 6000 kW/m ² , the surface temperature reaches 2110°C, while the temperature at a depth of 11 mm is 39°C. This behavior is achieved by the C–O–Si ceramic layer, which relieves thermal oxidation and aerodynamic erosion. The above results indicate that QFPRCs have the potential for practical applications in the aerospace field.