Ablation of carbon thermal protection system materials in high enthalpy air plasma

Two ablative thermal protection system materials were tested in the von Karman Institute for Fluid Dynamics’ 1200 kW Plasmatron facility. Carbon fiber preform (FiberForm) and carbon fiber weave were exposed to plasma air at four separate conditions to replicate moderate heat flux hypersonic flight conditions. Tests were conducted at a range of heat flux values between 12.5 W/cm² and 51.2 W/cm² and a range of chamber pressures between 0.64 kPa and 10.04 kPa. In-depth sample temperature, stagnation point surface temperature, high-speed camera data, and thermography image data were collected. High-speed image data was used to measure FiberForm stagnation point recession over time, and thermography image data was projected onto a static 3-D hemisphere to find temperature across the surface of a FiberForm sample as a function of position. Post-test scanning electron microscope images were collected for each sample, and fiber pitting and thinning due to fiber oxidation was observed. Uniformity and depth of oxidation of FiberForm samples at low heat fluxes suggests these experiments undergo reaction-limited or mixed regime oxidation, while high heat flux FiberForm experiments show evidence of diffusion-limited oxidation.