Multiaxial fatigue assessment of welded steel details according to the peak stress method: Industrial case studies

In fatigue design of welded joints, the Peak Stress Method (PSM) is an engineering, rapid, finite element-based tool to apply the notch stress intensity factor (NSIF) approach. The PSM presents some advantages, such as: (i) coarse meshes can be adopted, the required FE size being some orders of magnitude larger than that necessary to evaluate the NSIFs from the local stress distributions; (ii) only a single stress value is sufficient to estimate the NSIFs; (iii) 2D as well as 3D FE models can be used and (iv) the design engineer is able to determine the crack initiation point when competition between weld root and weld toe failure exists. Therefore the PSM may be a convenient design tool to adopt in the industry. In the present paper, new fatigue results have been generated by testing plate-to-tube welded steel details taken from industrial case studies under in-phase bending-torsion fatigue loadings. In particular, full-penetration joints adopted in the structure of a roundabout-type carousel and fillet-welded joints for quarter-turn scotch-yoke valve actuators have been tested. Experimental fatigue results have been analysed using the PSM, which proved to identify correctly the fatigue crack initiation location. Finally, a fairly good agreement has been obtained between the experimental results and the relevant PSM-based design curves.