Nuclear power plant components are often subjected to local plastic deformations due to low cycle operational thermal loading conditions. The fatigue behavior of weld seams is of particular interest in this context. Applicable design codes for fatigue life assessment use factors (e.g. Fatigue strength reduction factors – FSRF) within the simplified elastic-plastic or general elastic-plastic analysis in connection with the design fatigue curves for non-welded components. This way, the influence of the weld seam on the fatigue behavior is approximately considered. Emanating from this status quo ideas for a new approach considering the particularities of the fatigue behavior of the weld seam in more detail are developed. The proposed approach is based on material mechanics and constitutes a combination of experimental findings and numerical calculations in order to determine the local strains and the fatigue relevant influence of geometrical and metallurgical notches induced by the weld seam. Experiments on welded specimens provide the fatigue life as well as the stabilized cyclic stress-strain curve as relevant input parameters for the finite element analyses. The proposed model is capable of considering the exact geometry of the weld seam obtained by 3D scanning with very high resolution and the different material strengths due to the weld. The consideration of the principal influences on the fatigue behavior of weld seams paves the way to the application of established damage parameters such as PJ with the future objective to transfer the results also on arbitrary proportional and non-proportional loadings with variable amplitudes.

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