Modelling the effect of a spherical cavity on the fatigue limit of a 12% Cr steel

In a recent paper by HärkegÃ¥rd (2015), the effect of corrosion pits on the fatigue limit of 12% Cr steel was predicted based on an equivalent ΔK model for an annular crack at the equator of a spherical cavity. Predictions were compared with estimates due to Smith and Miller and Murakami and with data from fatigue testing. In the present study, four traditional methods for notch assessment have been added: Neuber's and Peterson's equations for the notch sensitivity, the 'support' factor due to the German FKM Guideline, and the 'point method' from the theory of critical distances (TCD). The seven methods have been applied to spherical cavities of various size in a 12% Cr steel. As expected, all methods predict the nominal stress range at the fatigue limit, ΔSA, to be a decreasing function of the radius of the cavity, r′. Models involving the threshold for fatigue-crack growth predict a fairly steep decrease of ΔSA from the intrinsic fatigue limit, ΔσA, in reasonable agreement with the trend of fatigue test data for members with corrosion pits, whereas the notch sensitivity and the FKM support factor predict a more gradual decrease.