Analylsis of Spallation Products using Arc-Jet Experiments

Spallation is a phenomenon in which solid particles are ejected off the surface of an ablative material in a high-enthalpy, high-shear flow field. The main contributor to this phenomenon in carbon-based heat shields is the mechanical erosion of carbon fibers weakened by oxidation decomposition. The dynamics of this phenomenon, which are poorly characterized in the literature, strongly affect the ablation rate of the material. In state-of-the-art codes, ablation by spallation is modeled using a "failure" ablation rate that is empirically determined. The present study aims at experimentally investigating spallation products ejected in the flow field and using this information to estimate the importance of spallation in the rate of ablation of low-density carbon/phenolic materials. Results from a test campaign at the NASA Langley HYMETS arc jet facility, including high-speed multi-camera imagery at 44,000 frames/second, will be used to reconstruct three-dimensional trajectories of spalled particles emitted from carbon-fiber samples exposed to an arc jet airflow. The purpose of this graduate fellowship request is to support Mr. Matthew Hardy's graduate research developing the particle tracking velocimetry analysis, and conducting analysis of the data obtained during two HYMETS test campaigns in which over fifty test conditions were investigated.