Fatigue assessment of local stresses at fillet welds around plate corners

During the fatigue assessment of welded joints very high stress peaks may be computed when applying local approaches. Finite element analyses show such high stresses for example in the fictitiously rounded toes of fillet welds around plate corners. However, fatigue tests of specimens containing this detail have not shown crack initiation from these spots in spite of the high stress peaks, but from adjacent, less stressed areas. This paper describes the fatigue tests and accompanying stress analyses, showing structural hot-spot stresses with moderate stress increase at the corners, however effective notch stresses magnified by the factor of 1.5 compared to the adjacent areas. Crack propagation analyses considering the steep stress gradient were performed to find an explanation for the observed fatigue behavior. Special considerations were necessary to obtain reasonable results for corner cracks because the stress intensity factors at the ends of the crack front are magnified by the notch of the weld toe. Another explanation for the fatigue behavior of the corners was found in the statistical size effects, where a proposal based on the highly stressed volume or weld length is applied. Finally, conclusions are drawn with respect to the consideration of local stress peaks in fatigue assessment approaches such as the effective notch stress approach.