Fatigue crack growth and closure at high cyclic strains

The concept of a cyclic J-integral (ΔJ) is considered, and equations are given for estimating its value. Fatigue crack growth rate data for an alloy steel are analyzed using ΔJ and rough crack closure measurements. Without the plasticity correction of ΔJ, there is an extreme lack of correlation for cases of cracks growing under reversed plastic strain. Including a correction for crack closure along with ΔJ gives good correlation of growth rates among various geometries and degrees of plasticity.