The Peak Stress Method combined with 3D finite element models to assess the fatigue strength of complex welded structures

Abstract

The Peak Stress Method (PSM) is a rapid and engineering application of the notch stress intensity factor (NSIF) approach for the fatigue strength assessment of welded structures, which employs the singular linear elastic peak stresses calculated by FEM using coarse meshes. First, the PSM was calibrated to rapidly estimate the NSIFs by adopting 3D, eight-node brick elements and by using the submodeling technique. Given the increasing 3D modelling of large and complex structures in the industry, the application of the PSM combined with 3D FE models has recently been speeded up by calibrating ten-node tetra elements, which allow to directly discretize complex 3D geometries making submodeling unnecessary. In the present contribution, the PSM has been calibrated by analysing several 3D mode I, II and III V-notch problems, by adopting either four-node or ten-node tetra elements. In particular, the 3D PSM with ten-node tetra elements has been extended to V-notch opening angles that had not been taken into account in a previous calibration, namely (i) 120° under mode I and (ii) 90° and 120° under mode III loadings. Then, an applicative example has been considered, which is relevant to a large-scale and rather complex steel welded structure, having overall size on the order of meters. The mesh density requirements to apply the PSM to the considered large-scale welded structure using either four-node tetra elements or ten-node tetra elements have been compared in order to assess the solution time required by the two types of FE meshes.