GRAPHITE AND ABLATIVE MATERIAL RESPONSE TO C02-LASER, CARBON-ARC, AND XENON-ARC RADIATION

摘要

This study investigated the behavior of graphite and several charring ablators in a variety of high-radiative heat-flux environments. A commercial-grade graphite and nine state-of-the-art charring ablators were subjected to various radiative environments pro¬duced by a CO2 laser and a carbon arc. Graphite was also tested in xenon-arc radiation. Heat-flux levels ranged from 10 to 47 MW/m². Tests were conducted in air, nitrogen, helium, and a CO2-N2 mixture which simulated the Venus atmosphere. The experimental results were compared with theoretical results obtained with a one-dimensional charring-ablator analysis and a two-dimensional subliming-ablator analysis. Neither the graphite nor the charring ablators showed significant differences in appearance or micro structure after testing in the different radiative environments. The performance of phenolic nylon and graphite was predicted satisfactorily with existing analyses and published material-property data. Good agreement between experimental and analytical results was obtained by using sublimation parameters from a chemical nonequilibrium analysis of graphite sublimation. Some charring ablators performed reasonably well and could withstand radi¬ative fluxes of the level encountered in certain planetary entries. Other materials showed excessive surface recession and/or large amounts of cracking and spalling, and appear to be unsuitable for severe radiative environments.