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 σrs introduced at the tip in SUS316 by overload Kov = 6, 15, 30 and 45 MPa·m1/2 can be estimated using Finite Element Method (FEM). The Krs values as a function of fatigue crack growth length Δa were calculated from the σrs according to Dugdale model. It was found that the calculated Krs decreased significantly with increasing Δa and reached to maximum value of |Krs|. Therefore, the maximum stress intensity factor Kmax will decrease apparently because of the action of Krs. As a result, effective stress intensity factor range given by ΔKeff = Kmax+Krs decreased with increasing Δa. Defining the fatigue crack cannot grow when ΔK eff = ΔKth, the apparent fatigue crack growth threshold ΔNKth can be estimated. Then, we can obtain the theoretical equation as ΔNKth=0.30K ov+4.10. The equation showed in good agreement with experimental results. © 2013 The Japan Society of Mechanical Engineers.