Abstract
EPRI organised an international research project [1], where ultrasonic testing was used to determine the fatigue limit of plain specimens of 12% Cr steel at R > 0 with artificially produced, sub-mm size corrosion pits. Moreover, the plain fatigue limit of uncorroded specimens was determined at R > 0, and fatigue-crack-growth testing, including the threshold, was carried out at R-values ranging from −1 to 0.9. This comprehensive set of fatigue data constitutes an ideal basis for investigating the capability of a variety of methods to predict the fatigue limit of pitted specimens. A pre-pitting procedure was used to produce single, nearly spheroidal corrosion pits as shown in Fig. 1. The semi-width-to-depth ratio r/d was typically around 0.5. It was therefore decided to model two extremes: a semi-spherical pit with r/d = 1 and a cylindrical “pit” with r/d = 0. To simplify the analysis, the fatigue behaviour of the semi-spherical surface pit was approximated by that of a spherical pore in a wide body. Consider an annular crack of depth a at the equator of a spherical pore. For a shallow crack, a a∗, the asymptotic stress intensity factor is given by
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