THE APPLICATION OF S-N CURVES CONSIDERING MISMATCH OF STRESS-CONCENTRATION BETWEEN TEST SPECIMEN AND STRUCTURE

This paper presents a procedure for the adjustment of S-N diagrams for noncontinuous welded joints in the fatigue analysis of structural det ails. The adjustment takes into account the effects of differences in geometry between the test specimen underlying the S-N curve and the hu ll structural detail it is applied to, considering the inelastic respo nse of material at the anticipated crack origin, multiple modes of loa ding, and their statistical correlation. The basis of the approach is a comparison of relative fatigue lives for the structural detail of in terest and the corresponding baseline specimen, using the local strain approach to fatigue, with extensions to the high-cycle regime. An S-N diagram so corrected is used in the conventional manner to predict fa tigue damage or to establish related allowable stresses. The procedure developed is thus entirely compatible with present fatigue life asses sment methods. The developed procedure is illustrated through numerica l examples.