Dynamic loading fracture tests of ferritic steel using the direct current potential drop method

Abstract

To apply the leak-before-break concept to nuclear piping, the dynamic strain aging of low alloy steel materials has to be considered, For this goal, J-R tests are needed over a range of temperatures and loading rates, including rapid dynamic loading conditions. In dynamic J-R tests, the unloading compliance method cannot be applied and usually the direct current potential drop (DCPD) method is used. But, the DCPD method is known to have a problem in defining the crack initiation point due to a potential peak that arises in the early part of loading of ferromagnetic materials. In this study, the characteristics of measured DC potential peaks were investigated for SA106 Gr. C piping steels, and the definition of crack initiation point was determined by backtracking from the physically-measured final crack length. It is proposed that this technique could be applied as an improved DCPD method applicable for the dynamic loading J-R test.