The purpose of this study is to evaluate the effects of burn-off at 500°C by air oxidation on strengths and fracture toughnesses of a carbon-fiber-reinforced carbon composite and three finegrained isotropic graphite materials that are used as main materials of plasma facing components for fusion reactor devices and core structural materials of gas-cooled nuclear reactors. The Young's modul, the bending strengths, the Rockwell hardnesses, the mode I fracture toughnesses and the load and depth by a manufactured hardness tester were measured and the microstructures of the fracture surfaces were examined. The degradations due to burn-off of these properties of CX-2002 U composite were the smallest and those of IG-430 U graphite were less marked than those of other graphite materials. After oxidation of the C/C composite, preferential removal of the boundary layer between carbon fiber and pyrolytic carbon matrix and carbon fiber were observed. After oxidation of graphite materials, the size and the number of pores were increased and the fracture surfaces were rough due to oxidation of graphite grain boundaries.
