Investigation on Path-Integral Expression of the J-Integral Range Using Numerical Simulations of Fatigue Crack Growth

Abstract

Fatigue crack growth rates under elastic-plastic conditions have been reported to correlate well with the J-integral range, ΔJ, evaluated experimentally from load-point displacement using formula developed for specific specimen configurations. However, the theoretical basis of ΔJ still remains unestablished. in this paper, path-integral expressions of ΔJ and their approximate path-independence in the presence of the effects of strain hardening and crack closure were discussed. Finite element simulations of elastic-plastic crack growth under cyclic loading were conducted. It was found that ΔJ values evaluated by the path-integral were almost path-independent when the minimum load point or the crack opening point was selected as a reference point for evaluation. The examination of the relationship between ΔH and crack-tip opening displacement or strain distribution near the crack tip led to the conclusion that ΔJ evaluated on the basis of the crack opening point was the most appropriate parameter in characterizing the near-tip-stress and strain fields under fatigue conditions.