抄録
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 σ_<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 Δ_α were calculated from the σ_<rs> according to Dugdale model. It was found that the calculated K_<rs> decreased significantly with increasing Δ_α 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 ΔK_<eff>=K_<max>+K_<rs> decreased with increasing Δ_α. Defining the fatigue crack cannot grow when ΔK_<eff>=ΔK_<th>, the apparent fatigue crack growth threshold Δ^NK_<th> can be estimated. Then, we can obtain the theoretical equation as Δ^NK_<th>=0.30K_<ov>+4.10. The equation showed in good agreement with experimental results.
