Realistic fatigue life prediction of weld toe and weld root failure in load-carrying cruciform joints by crack propagation analysis

摘要

At load-carrying cruciform joints weld fracture due to cyclic loading occurs either at weld toe or at weld root, mainly depending on the ratio between plate and weld throat thickness. For a weld shape optimization a reliable prediction of the critical fatigue crack is of interest and can be assured by limit curves derived from experiments or, alternatively, by different approaches of fatigue assessment. In this paper three common approaches are applied to a selected geometry aiming to benchmark their quality with respect to the fatigue assessment and the prediction of the failure critical notch. Here, disagreement with tests occurs when a two-dimensional crack with a constant depth along the weld seam is assumed. Therefore, different possibilities reaching a more realistic fatigue life assessment are analyzed and it is shown how a semi-elliptical crack front at the weld toe can be included in the crack propagation analysis. Moreover, several solutions are presented in order to estimate a proper aspect ratio together with their influence on the stress intensity factors and life cycles. For the improved crack propagation analysis a solid model is generated by finite elements and different crack sizes at the weld toe are investigated. It turned out that creating the crack front and its direct connection to the weld seam as well as the estimation of stress intensity at the plate surface are the challenging tasks. The three-dimensional crack propagation analyses prove that the total remaining lifetime is more realistic if a semi-elliptical crack front is taken into account. This, finally, leads to identify the critical location of crack initiation correctly and confirms the results of experimental evaluation and stress-based approaches.