Modeling of Overload Effect on Fatigue Crack Growth Threshold Using Finite Element Method

Abstract

A model of overload effect for hardening elastic-plastic solids is proposed to evaluate the stress intensity factor for compressive residual stress K rs at fatigue crack-tip fields. The residual stress  rs introduced at the tip in SUS316 by overload K ov = 6, 15, 30 and 45 MPam 1/2 can be estimated using Finite Element Method (FEM). The K rs values as a function of fatigue crack growth length a were calculated from the  rs according to Dugdale model. It was found that the calculated K rs decreased significantly with increasing a and reached to maximum value of |K rs |. Therefore, the maximum stress intensity factor K max will decrease apparently because of the action of K rs. As a result, effective stress intensity factor range given by K eff = K max +K rs decreased with increasing a. Defining the fatigue crack cannot grow when K eff = K th , the apparent fatigue crack growth threshold   K th can be estimated. Then, we can obtain the theoretical equation as   K th =0.30K ov +4.10. The equation showed in good agreement with experimental results.