A consideration of allowable equivalent stresses for fatigue design of welded joints according to the notch stress concept with the reference radii rref = 1.00 and 0.05 mm

In the literature, allowable stresses (FAT-values) for the fatigue design of welded joints are established according to the notch stress concept with the reference radii r(ref) = 1.00 mm for thick connections (t >= 5 mm) and 0.05 mm for thin connections (t < 5 mm). However, it is not clear for which strength hypothesis they are valid. As local equivalent stresses may be calculated by the principal stress or von Mises hypotheses, it is necessary to distinguish between the applied hypotheses. The FAT-values according to the principal stress and von Mises hypotheses are compiled for steel, aluminium and magnesium for the reference radii r(ref) = 1.00 and 0.05 mm. The allowable stresses are derived from normal as well as from shear stresses. However, the values derived from pure normal loading (axial or bending) and from pure torsion are not compatible when the principle stress or the von Mises hypotheses are applied. Therefore, in case of biaxial loading, the stated incompatibility between the values obtained from different loading modes should be overcome by the Gough-Pollard relationship.