Influence of residual stresses on fatigue strength of large-scale welded assembly joints

Residual stresses (RS) are known to affect fatigue strength of welded structures in some way. The amount of these residual stresses depends on heat input, the volume of the weld deposit, the number of passes in each weld, and the number of adjacent welds. Therefore, residual stress states are of interest in the design state already. However, determination possibilities by measuring are limited and costly. Numerical welding simulation might be helpful. However, numerical welding simulation still is a challenging task, especially in large-scale modeling and multi-pass welding, calling for simplified methods and models. Even if one is able to calculate residual stresses, their effect on fatigue strength of large-scale welded structures remains uncertain. During fatigue assessment, it is often assumed that tensile residual stresses up to yield strength of the material are present. On the other hand, it is known that residual stresses are redistributed during cyclic loading, thus reducing their effect on fatigue. In this work, experimental and numerical investigations on large-scale components are presented. Fatigue tests were performed and residual stresses (X-ray) were determined at different states, before and during cyclic loading. Calculated and measured results are compared. The influence of residual stresses on fatigue strength with respect to cyclic redistribution is discussed. This paper represents some of the most meaningful results of a recently finished research project. Further information and results in more detail of this work can be found in the report of Dilger et al. (AiF-Schlussbericht, IGF-Vorhabennummer 17652N, 2016).