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 formulae developed for specific specimen configurations. However, the theoretical basis ofΔJ still remains unestablished. In this paper, path-integral expressions ofΔJ 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 level or the crack-opening level was selected as a reference level for the evaluation. The examination of the relationship between ΔJ 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 level was the most appropriate parameter characterizing the near-tip stress and strain fields under fatigue conditions.