Fatigue Assessment of Weld Toe and Root Cracks with the Notch Stress Intensity Factor and Crack Propagation Approach

摘要

Fatigue is still a concern in shipbuilding. Several fatigue failures are initiating from the root of non-penetrating welds, which are widely applied in shipbuilding. The structural optimisation andreduction of weld material increase the danger of root cracking. The fatigue assessment during design is mainly based on the nominal, structural hot-spot or notch stress approach. These approaches are only partly applicable to weld roots, give rough estimates such as the nominal stress approach or over-conservative life predictions such as occasionally the notch stress approach when keyhole notches are modelled. A better prediction is expected from the crack propagation approach assuming the non-welded root gap and a short crack at the weld toe as initial cracks. Another new approach is the notch stress intensity factor approach (N-SIF approach) which is able to assess the fatigue life of V-shaped notches at weld toes as well as weld roots using the strain energy density around the notch. Both approaches are applied to different joints where toe and root failures are probable. The results are compared with previous analyses using the other approaches mentioned. Fatigue test results are also available for a comparison which allows to draw conclusions with respect to the approaches for an appropriate fatigue strength assessment.