Influence of residual stress relaxation and microstructural changes on the possibilities of fatigue life prediction of welded joints

The presented investigations have been carried out in order to improve the reliability of life prediction methods for fatigue loaded welded components. Therefore, the microstructural changes and the residual stress relaxation in different zones of the weld seam in specimens and in welded components were examined systematically. The microstructural changes, like the decrease or increase of the dislocation density depending on the initial properties of the weld and the base metal, the residual stresses and the load conditions can be correlated with the probability of fatigue cracking and therefore with the resulting lifetime. The microstructural changes can be correlated with parameters which can be easily measured with a micromagnetic measurement method. In comparison with fatigue test results, e. g., with corresponding S - N curves, the measured micromagnetic parameters can be used for a linear multiparameter regression calculation in order to use these parameters for a concrete lifetime prediction.