Structural Hot-Spot S - N Curves

At first, general principles of the fatigue assessment approach using S-N curves are outlined, including the formula describing the design fatigue life in relation to the structural hot-spot stress range and the modification in the high-cycle regime to consider damaging effects under variable amplitude loading. Also the detrimental plate thickness effect may require a modification of the S-N curve. Further hints are given regarding the effects of misalignments. Afterwards, the two design S-N curves recommended for the conventional structural hot-spot stress approach are defined, one applicable to butt and non-load carrying fillet welds and the other to load carrying fillet welds. Finally, the S-N curves used in the other structural stress approaches are described, whereby a special structural stress parameter is needed in Dong’s approach.