Understanding High Recession Rates of Carbon Ablators Seen in Shear Tests in an Arc Jet

High rates of recession in arc jet shear test s of Phenolic Impregnated Carbon Ablator (PICA) inspired a series of tests and analysis on FiberForm (a carbon preform used in the fabrication of PICA). Arc jet tests were p erformed on FiberForm in both air and pure nitrogen for stagnation and shear configurations . The nitrogen tests showed little or no recession, while the air tests of FiberForm show ed recession rates similar to that of PICA (when adjusted for the difference in density). While mechanical erosion can not be ruled out, this is the first step in doing so. Anal ysis using a carbon oxidation boundary condition within DPLR was used to predict the recession rate of FiberForm. The analysis indicates that much of the anomalous recession behavior seen in shear tests may simply be an artifact of the non-flight like test conf iguration (copper upstream of the test article) a result of dis- similar enthalpy and oxygen concentration profiles on the copper. Shape change effects were also investigated and shown to be relatively small.