Characterisation of residual stress relaxation in fatigue loaded welded joints by X-ray diffraction and Barkhausen noise method

The fatigue behaviour of welded joints is dependent on the weld geometry, its microstructure, the cyclic material properties of the different weld zones and the magnitude and relaxation behaviour of residual stresses. The degree of plastic deformation and the quasi-static residual stress relaxation in the weld was simulated by a FEM-model and coincided well with the residual stresses measured by X-ray diffraction. Under fatigue loading, an advancing residual stress relaxation in the weld is accompanied by a characteristic change in the micromagnetic parameters resulting from the Barkhausen noise measurements. Using a multiparameter regression approach, the problem of ambiguity of micromagnetic parameters can be solved and the micromagnetic testing method can be used for the residual stress determination in welded joints. The results indicate that a characteristic change of the residual stresses and in the behaviour of the micromagnetic parameters shortly before failure of the welded joint can be used as an indicator of severe fatigue damage within the weld.