Experimental Investigation of Strain Concentration Evaluation Based on the Stress Redistribution Locus Method

Evaluating the local strain in structural discontinuities is an important technology in high temperature design of fast reactor components because the failure mode in high-temperature fatigue or creep fatigue damage usually results from the crack initiation and growth from such locally high strained areas. A rationalized method of evaluating strain concentration that was experimentally studied is discussed. The stress redistribution locus (SRL) method had been proposed to improve the accuracy with which local stress and strain can be evaluated in the structural discontinuities. This method is based on the concept that the locus of stress redistribution from an elastic to an inelastic state, or that during relaxation, strongly depends on the structure, and the locus almost coincides with the locus obtained through elastic-creep analysis. High-temperature fatigue tests of circumferentially notched specimens were conducted accompanied by the measurement of local strain carried out with a capacitance-type strain gauge. The measured strain was compared with the predictions made with SRL, and the method's accuracy was evaluated. SRL improved the accuracy of inelastic strain estimation while remaining reasonably conservative in comparison with Neuber's rule, which is used in high temperature design codes.