High cycle thermal fatigue crack growth and high temperature crack growth law

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In order to simulrate the thermal striping situation in the sodium-cooled components of fast breader reactors, an apparatus was developed in which a high frequency of 1Hz in thermal stress cycling was applied to the test sample by a combination of direct current heating and cyclic shower. Crack growth tests were conducted for austenitic stainless steep plate samples of 10mm in thickness with a small semi-circular precrack of 0.4mm in diameter under the three levels (low, intermediate and high) of thermal stress cycling. The surface temperature of the sample was 540*80ﾟC in the intermediate level in the thermal stress cycling. The crack was accelerated in the first stage of growth, but it was decelerated for further growth after for any level of thermal stress cycling. The crack finally stopped growing under the low level of thermal stress cycling at a crack length of 0.6mm in a thickness direction. A leser speckle displacement gage was developed and used to monitor the crack opening and closure of the growing crack under thermal stress cycling. The thermal stress was estimated by the finite element analysis by using the temperature distribution obtained experimentally. The stress intensity factor was also estimated on the basis of this thermal stress. The correlation between the crack growth under thermal stress cycling and that under conventional stress cycling at constant temperatures was discussed. Both the data were found to be adjusted by the effective range of the stress intensity factor.