Some advantages derived from the use of the strain energy density over a control volume in fatigue strength assessments of welded joints

In the notch stress intensity approach to the fatigue assessment of welded joints, the weld toe is modelled as a sharp V-notch, ρ = 0, and local stress distributions in plane configurations are given on the basis of the relevant mode I and mode II notch stress intensity factors (NSIFs). The local strain energy density over a circular sector surrounding the point of singularity can be easily calculated as soon as the NSIFs are known. Whilst the NSIF evaluation needs very fine meshes in the vicinity of the points of singularity, which is a drawback of the approach in the presence of complex geometries, the mean value of the elastic SED on the control volume can be accurately determined by using relatively coarse meshes. This fact is demonstrated here by using a number of FE models with very different mesh refinements. Both bi-dimensional and three-dimensional welded details are considered showing degree of accuracy and limits of applicability of the method. Thanks to the SED use, the degree of refinement of FE models is not so different from that usually used to determine the ‘hot-spot stress’ according to the structural stress approach.