Assessment of multiaxial fatigue behaviour of welded joints under combined bending and torsion by application of a fictitious notch radius

A major problem in the assessment of the multiaxial fatigue behaviour in welded joints is the determination of local notch stresses, since the real local radii in most cases are not known. This can be circumvented by introducing a fictitious notch radius, according to Neuber and Radaj. The calculations of local equivalent stress amplitudes for welded joints (tube–tube and flange–tube) under pure bending, pure torsion and combined in- and out-of-phase bending with torsion can then be carried out by stress-based and strain energy density-based criteria. Among the investigated methods, the most reliable results are obtained with the effective equivalent stress hypothesis, an integral interference plane oriented method, which transfers the results of complex loadings onto the safe side of the reference scatter band for pure bending. However, the best fit with the reference scatter band is realized by the application of the maximum shear and normal strain energy density parameter in the critical plane.