Influence of weld quality on the fatigue strength of thin normal and high strength steel butt joints

For building more energy-efficient and eco-friendly structures, new lightweight solutions are needed. Utilization of higher strength steels and smaller plate thicknesses together with modern welding technologies holds a huge potential for weight reduction. However, due to lack of knowledge about the fatigue resistance, current rules do not allow using smaller plate thicknesses than 5 mm nor benefiting from higher strength steels in large welded structures such as in ships. One of the main concerns in addition to larger welding-induced distortions is the weld quality. This paper compares the fatigue strength of 4 mm thick normal and high strength steel butt joints produced by different welding methods leading to different weld shape and quality. In order to eliminate the effect of secondary bending due to initial distortions and bring out the influence of weld quality, the fatigue test results are analyzed using structural hot spot stress approach with measured specimen geometries. The results show considerable yield-limit-dependent increase in the fatigue strength of high quality welds, while no benefit from higher base material strength was observed for low quality butt joints. In addition, the suitability of existing weld quality recommendations for thin welded joints was evaluated and future research needs discussed.