Fatigue limit evaluation of notches, small cracks and defects: an engineering approach

In this paper, the average stress method for the fatigue limit evaluation of stress raising geometrical effect is revised and extended. The linear elastic stress equations have been modified by taking into account the nominal stress on the local tangential stress. Hence, in a close interval 2a0, where a0 is El Haddad’s short crack constant, the average stress and related fatigue limit estimations were evaluated in the case of long and small notches and crack like-notches. The typical curves on the Kitagawa-Takahaschi diagram are obtained, for all geometrical discontinuity, as far as crack-like notch becomes small; similarly the notch sensitivity is estimated as far as the tip radius reduces by using always the “average stress” criterion. . The accuracy of the proposed method in predicting fatigue limits was also checked by using experimental data, taken from the literature, concerning specimens weakened by rounded and sharp notches as well as small artificial defects.