Effect of helium to dpa ratio on fatigue behavior of austenitic stainless steel irradiated to 2 dpa

The effect of helium due to nuclear transmutation reactions during neutron irradiation on low cycle fatigue life of type 304 stainless steel was inves tigated. The specimens were irradiated in spectrally tailored capsules in t he Japan Materials Testing Reactor (JMTR) at a temperature of 823 K to a ne utron fluence of approximately I x 10(25) n/m(2) (E > 1 MeV) and helium lev els of 0.8, 2.5 and 8.1 appm. The low cycle fatigue tests were performed in total axial strain ranges of 0.8-1.6% at 823 K. A laser extensometer was u sed for controlling the axial strain of a specimen under cyclic testing. Th e difference between unirradiated and irradiated specimens is quite clear a nd appears to be a reduction by a factor of 2-5 in fatigue life. The helium concentration of the specimen is not the main factor to shorten fatigue li fe in the present experimental condition. (C) 2000 Elsevier Science B.V. Al l rights reserved.