Evaluation of the fatigue strength of notched specimens by the point and line methods with high stress ratios

The point and line methods proposed by Taylor have been used to predict the fatigue strength of notched specimens with different stress ratios R by using literature experimental results. Predictions have been carried out by taking advantage of several equations describing the material fatigue strength dependence on the mean stress and the results obtained by using the Goodman and the Smith–Watson–Topper (SWT) equations are shown. Predicted and experimental fatigue strengths have been compared showing that the effectiveness of the point and line methods can be increased by introducing equivalent mean and alternating stresses and by introducing the dependence of the El Haddad parameter a0 on the stress ratio R. Also with these corrections, the gap between predicted and experimental fatigue strengths for high R stress ratios still keeps being large. It is shown that the gap between predicted and experimental fatigue strengths for high R stress ratios can be reduced by introducing the experimentally evaluated mechanical properties of the material at different stress ratios R and/or by introducing the SWT fatigue strength approximating equation.