Prediction Method of Elastic-Plastic Fatigue Crack Growth Rate under Variable Amplitude Loadings

Abstract

Load-controlled fatigue crack growth tests were carried out under reversed and pulsating repeated variable amplitude loadings in post-yield region. Crack growth increment and crack closure were measured by the minicomputer-aided unloading elastic compliance method. The effects of load variation on the elastic-plastic fatigue crack growth behavior and the application of range-pair counting method to j-integral, ΔJ^*, for estimation of crack growth rates, where both one-directional and cyclic plastic deformation were observed remarkably, was discussed. It was found that fatigue crack growth rates under reversed varying loadings were estimated by the linear summation rule based on ΔJ^*, and fracture mechanics parameter ΔJ^*/(1-J_max/C), where J_max is the maximum J-integral, should be used for estimation of growth rates of fatigue cracks where residual one-directional plastic deformation occurred as was observed under pulsating varying loadings.