Laser welded overlap tubular joints of an AZ31 magnesium alloy show an unexpected failure behaviour under axial and tensional cyclic loading. In the as-welded condition the fatigue cracks propagate not from the locations with the highest load stress concentration but from other sites. After a stress relief annealing at relatively low temperatures the crack initiation sites change to the expected locations This specific behaviour can be found on overlap connections of tubular joints as well as

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... aluminium as in magnesium alloy joints. Combined FE-calculations and residual stress measurements by means of XRD and neutron diffraction reveal that the particular constraint conditions of tubular joints lead to residual stress distributions which are distinguished remarkably from those of flat plates with linear welds due to the self-constraining geometry. The generation of a non-uniform circumferential residual stress condition with particular locations of high tensile and compressive residual stresses may explain the observed failure behaviour. After an annealing process with strong residual stress relaxation the fatigue cracks start at the expected locations. A shrinkage model for the description of the residual stress generation in tubular joints explains the local residual stresses over the entire thickness in the weld zones and in the adjacent material.