Requirements for stress gradient-based fatigue assessment of notched structures according to theory of critical distance

Notches, local stress raisers within structural components, are one of the most important locations for fatigue crack initiation. It is well known that fatigue is governed by the effective stresses in the vicinity of notches. Within this study, differences in prediction accuracy between different types of theory of critical distance methods, that is, point and line methods, are systematically investigated in conjunction with a sensitivity study regarding mesh refinement, assumed strength hypothesis and material behaviour. For this purpose, a finite element analysis parameter study on notched structures is performed and recommendations for the application of stress gradient methods are presented. Difference in effective stress of up to 30%, and hence a significant difference in fatigue life (e.g., 185% for a slope of S-N curve of k = 4), is found for typical notch shapes, for example, in welded joints.The work was performed within the research project ESM-50 ‘Fatigue of welded structures at sub-zero temperatures’, funded by the German Research Association of the Working Group of the Iron- and Metal-processing Industry e.V. as part of the Donors' Association for the Promotion of Sciences and Humanities in Germany under project number AVIF-No. A301