FATIGUE LIMIT AND GEOMETRICAL AND STATISTICAL SIZE EFFECT

The ratio of the fatigue limit of an unnotched specimen to that of a notched one, the fatigue notch factor K(f), is usually smaller than the theoretical stress concentration factor K(t). With the assumption of a plastic cyclic deformation epsilon-apW at the level of the fatigue limit the fatigue limit for a notched specimen can be calculated. According to formula (4) this fatigue limit sigma-naD is a function of K(t), epsilon-apW, the notch stress amplitude sigma-a, the cyclic strengthening exponent n' and the fatigue limit of a smooth specimen sigma-W. Moreover, taking into account the statistical size effect with the known "weakest link concept", see flow chart Fig. 9, the calculation is in a good agreement with 77 test results for steel.