Fatigue strength of laser-dressed non-load-carrying fillet weld joints made of ultra-high-strength steel

Abstract

Laser dressing or remelting is one of the post-weld treatment methods that is based on the modification of the local weld toe geometry, and generally, it is similar to TIG or plasma dressing. However, the laser dressing is not covered by common fatigue design guidelines and recommendations of welded structures at the moment. In this research, the effect of laser dressing on the fatigue performance of non-load-carrying fillet-welded cruciform joints made of direct quenched S960 grade steel was studied by means of experimental fatigue testing and geometry and residual stress measurements together with finite element analyses and different statistical calculation processes, such as nominal, structural and effective notch stress methods. In addition, the 4R method was also employed and its applicability for fatigue assessment of laser-dressed weld joints in question was investigated. The experimental results showed the enhancement of the fatigue strength for laser-dressed fillet weld joints compared to as-welded condition and the recommended FAT class for similar TIG dressing case was exceeded. However, the fatigue strength improvement of laser dressing was less compared to the corresponding TIG-dressed joints when applied stress ratio was low. In proportion, the disparity between the improvement effect of laser and TIG dressing methods was reduced with higher applied stress ratio. This can be explained by different residual stress state in the critical weld toe treatment area of laser- and TIG-dressed joints that can be taken into account when using the 4R fatigue assessment method.