Fracture mechanics studies on fatigue crack growth under elastic-plastic condition is usually characterized by J integral range, ΔJ determined by an approximation from area under load-displacement hysteresis loop developed by Dowling and Begley. Despite being supported by some experimental data which reported that fatigue crack growth rates under elastic-plastic conditions have good correlations with ΔJ, the applicability of ΔJ on crack growth in a material subjected to cyclic bending remains inconclusive. In this study, finite element analysis of a four point-bending rectangular plate model with an edge crack length a/W between 0.1 to 0.5 was carried out under displacement amplitude δ a between 0.1 to 1.5 mm to represent small to large scale yielding conditions. The elastic component was found to be the driven force of fatigue crack growth parameter in small scale yielding (SSY) condition while in large scale yielding (LSY) condition, the plastic component must be considered. It was also found that the simple method of ΔJ-integral calculation using load-displacement approach is overestimated for shallow crack under LSY condition.
