Fatigue strength assessment of hybrid laser arc welded structural steel components for civil applications

In this project thesis, the fatigue behaviour of hybrid laser-arc welded joints was investigated by means of local approaches. The welded components experimentally tested under fatigue loadings are made of structural steel and represent joints for civil engineering applications, in particular for the construction of a bridge in Norway for Stetens Vegvesen. Firstly, T-joints were experimentally tested under pure axial fatigue loading, stake L-welds were tested under shear fatigue loading and butt joints were tested under pure axial fatigue loading. After that, their fatigue strength has been assessed by local approaches based on numerical simulations performed by using the finite element software Ansys®. The purpose of the analyses was to apply SED, PSM and Hot spot methods and to compare the FE results with the fatigue design scatter bands available in the scientific literature for each approach. Since the full-scale bridge panels were also fatigue tested, a 3D modelling of the test specimen was subsequently carried out by taking care to the welded details (T-weld and Stake L-welds) and it was also studied with the finite element software Ansys®. The purpose here was to properly simulate the experimental test conditions in order to asses the behaviour of the specimen in terms of stress and strains. In particular, the aim was to compare FEM results with the experimental ones provided by the strain gauges attached to the test specimen.