Quantification of spalling particles for carbon thermal protection system materials in supersonic air and nitrogen plasma

A quantitative investigation on the spallation effect of carbon fiber preform (FiberForm) in supersonic high-enthalpy plasma air and nitrogen was conducted in the Center for Hypersonics and Entry System Studies (CHESS) Plasmatron X inductively coupled plasma wind tunnel at the University of Illinois Urbana-Champaign. FiberForm wedge samples with half-angles of 15◦ and 30◦ were subjected to supersonic plasma air and nitrogen flow with a nominal cold-wall heat flux of 675 W/cm² and a stagnation pressure of 6750 Pa. Along with sample surface temperature and mass loss data, high-speed images were captured during each test; this high-speed image data was used to measure particle trajectories at each condition, allowing for analysis of average particle velocity and cumulative particle density fields. Highly unsteady spallation behavior was observed for experiments conducted in supersonic nitrogen plasma, and statistical analysis was utilized to demonstrate differences in spallation time variation between air and nitrogen plasma experiments.