Abstract
The effect of oxidation on tensile strength, fracture toughness and crack extension rate was examined for an isotropic fine-grained graphite IG-11, a candidate material for the graphite components of an HTGR. Oxidation tests were performed at 500°C in air. Drastic decreases in tensile strength and fracture toughness values after oxidation were observed. The ratio of their values after oxidation to those before oxidation decreased with increasing the ratio of the apparent density after oxidation to that before oxidation. The crack extension rate da/dN was well expressed as da/dN=0.454(ΔK-Δkth)4.0, where the value ΔKth decreased as oxidation proceeds. As a result, the crack extension rate increased with increase of burnoff level. The result was considered to be due to the formation of pores less than 1 μm and that of larger pores which were observed on the fracture surface of oxidized specimens.
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