Assessment of the fatigue behaviour of welded aluminium joints under multiaxial spectrum loading by a critical plane approach

Multiaxial stress states occur in many welded constructions like chemical plants, railway carriages and frames of trucks. Depending on the loading mode, those stresses can have constant and changing principal stress directions. For welded fine grained steel, research results show a severe loss of fatigue life for changing principal stress directions simulated by out-of-phase bending and torsion compared to constant directions given by in-phase loading. However, aluminium welds reveal no influence of changing principal directions on fatigue life compared to multiaxial loading with constant principal stress directions under constant amplitude and spectrum loading. This behaviour is not predictable by any conventional hypothesis. A hypothesis on the basis of a combination of local normal and shear stress in the critical plane has been developed and successfully applied to aluminium weldings.