Fatigue failure and fracture mechanics of graphites for high temperature engineering testing reactor

Abstract

The effect of stress ratio, irradiation, oxidation, specimen volume and cumulative damage on fatigue behavior and fracture toughness were examined for HTTR (High Temperature Engineering Test Reactor) component materials, IG-110 and PGX graphites, and the following conclusions were derived: The fatigue strength of IG-11 graphite, which is non-purified IG-110 graphite, decrease with decreasing stress ratio and crack extension speed was enhanced mainly by the increment of cyclic peak load. The increment of fatigue strength of IG-110 graphite irradiated at the temperature of 575-650°C and neutron fluence of up to 1.92 × 1020-3.20× 1020 n/cm2 corresponds to that of the static strength of irradiated one. The fatigue strength of IG-110 graphite oxidized at 500°C in air can be inferred by the S-N curve analysis and the rule of degradation of static strength and crack extension speed of oxidized IG-110 graphite was enhanced as oxidation proceeds. Cumulative fatigue damage Df of High-Low typed fatigue test for IG-110 graphite were smaller than the values estimated by the Miner's low, whereas the values of Df of LowHigh tests were larger than the values estimated by the Miner's low. © 1991 Taylor & Francis Group, LLC.