On the effect of weld defects on the fatigue strength of beam welded butt joints

Abstract

Modern guidelines concerning the fatigue strength of welded components are often based on the nominal stress concept. These guidelines are valid for fusion welded steels but do not distinguish between different welding processes. However, different welding processes can lead to significant differences in the resulting weld geometry. This is particular true for arc welded components in comparison to beam welded components. Furthermore, it is well known, that the geometry of welded joints effects the fatigue strength severely. Therefore, it can be expected that beam welds behave differently to arc welds in fatigue tests. In this study, electron beam and laser beam welded samples of different thicknesses made from fine-grained steels were tested in fatigue tests under a constant amplitude loading. In order to assess the effects of weld defects on the fatigue strength, samples with defined weld defects (e.g. axial misalignment) were included in the study as well. The weld geometry of each sample was measured and evaluated according to the quality groups in ISO 13919-1. Additional numerical notch stress calculations were performed. Finally, a correlation between the quality groups according to ISO 13919-1 and the nominal cyclic stress at 2*106 load cycles with a survival probability of 97,5% was proposed. This correlation allows users of beam welding processes to predict the fatigue strength of components under the condition that certain quality levels according to ISO 13919-1 are met.