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: (1) 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. (2) The increment of fatigue strength of IG-110 graphite irradiated at the temperature of 575-65o•c and neutron fluence of up to 1.92 x 10" 0-3.20 x 10" 0 njcm 2 corresponds to that of the static strength of irradiated one. (3) The fatigue strength of IG-110 graphite oxidized at soo•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. (4) Cumulative fatigue damage D 1 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 n, of Low-High tests were larger than the values estimated by the Miner's low.

A 3D full‐field study of cracks in a nuclear graphite under mode I and mode II cyclic dwell loading conditions

“…16 A few studies of fracture from notches have been carried out under mode II 26,27 and mixed mode 28,29 loading conditions, and the notch sensitivity of graphite has also been investigated using a strain energy density approach. 28,29 Some early studies 3,[30][31][32][33] have reported fatigue crack growth and fatigue lives of nuclear graphite. However, these offer limited insight into the material behaviour during crack growth under cyclic loading conditions, mainly due to the limitations in the methods of studies in the past.…”