Low Cycle Fatigue of Seam Welds – Numerical Simulation under Consideration of Material Inhomogeneities

Abstract

Austenitic stainless steel of type X6CrNiNb18-10 is a commonly used material for pipelines of power plants. The fatigue behavior of these components is often operationally determined by thermo-mechanical stresses. Welded joints are subjected to various geometries and micro structural inhomogeneities, which lead to complex stresses in the component. This is the reason for a reduced fatigue life, in contrast to material's life itself, is observed.A parametric finite element model is developed, to investigate the influence parameters. In order to take into account the non- uniform hardness distribution in the region of the weld seam, hardness measurements are the base for the consideration of a material mismatch in plastic behavior. The material parameters for the used Chaboche material model must be modified individually, depending on the mismatch. In addition, the consideration of imperfections of the welding geometry is an important factor, too. Using a local approach by using measured geometry-parameters of the weld seam, acceptable accordance between experimentally and numerically calculated fatigue lives can be gained. The observed phenomena in experimental investigations that fatigue failure occurs either at the base metal or at the weld toe (depending on the loading conditions) can be reproduced by numerical simulations. This knowledge is used to develop an approach for lifetime estimation.