Consideration of imperfections and support effects in the fatigue assessment of welded cruciform joints

Abstract

Abstract The strain-life approach appears to be a powerful tool to design components against fatigue failure. Given its general theoretical background, it may be applied to a wide range of cases. In the contribution at hand, its application to welded components, and especially the incorporation of size effects in the concept has been investigated. For this purpose, eight welded cruciform joints were tested for fatigue at two different load amplitudes, accompanied by supplementary investigations such as hardness measurements and tensile tests. The observed fatigue lives were compared to numerically estimated ones. Special attention was paid to the consideration of imperfections in the calculations. The weld geometries were modeled once using an idealized shape and once with a realistic representation obtained by 3D-laser scanning. Additionally, different methods to approximate cyclic material parameters were investigated. The results show an improvement in prediction accuracy if the real weld geometry is used. However, by doing so, the incorporation of size effects via a highly stressed area is open for discussion. Due to the high local stress and its steep gradients, as a result of the scanned weld surface, the calculated areas are very small, which raises the question whether this is still within the limits of its application. Regarding prediction accuracy, the fatigue lives of either one or the other load amplitudes were properly estimated. This issue may be addressed by modifying the slope of the strain-life curve for welded components, which can be achieved by a parameter fitting procedure through a large set of experiments.