Multiaxial fatigue assessment of tube-tube steel joints with weld ends using the peak stress method

In the context of fatigue design of welded structures, the peak stress method (PSM) is a rapid numerical technique in engineering that applies an approach based on notch stress intensity factors (NSIFs). To estimate NSIFs, the PSM requires only a single stress value calculated using either 2D or 3D finite element (FE) models discretised using coarse meshes, with the adoptable element size being some orders of magnitude larger than required to calculate the NSIFs based on local stress fields. In this study, the PSM was applied to the fatigue assessment of tube-tube steel joints with weld ends subjected to combined loadings: pure axial, pure torsion, inphase and out-of-phase axial-torsion loadings, all with two load ratios, i.e., R = 0 and R = -1. Experimental fatigue results generated in a previous study by some of the authors have been reanalysed in this study through the application of PSM to 3D FE models, including an idealised weld end geometry. The experimental fatigue crack initiation location was properly estimated using PSM, and there is good agreement between the experimental results and the relevant PSM based design curve.