Fatigue assessment of laser hybrid welded butt joints with severe imperfections using 3D scanning and critical distance theory

Abstract Laser -hybrid welded butt joints are increasingly used in structural applications due to their high productivity. However, the complex interaction between the laser beam and arc process often leads to weld imperfections. These weld imperfections can significantly influence the development of stress concentrations on the weld surface, which can affect the mechanical properties and fatigue performance of the joints. Therefore, accurately identifying and assessing these imperfections is crucial for ensuring weld quality and structural safety. In this study, a method is proposed to assess the weld quality and numerically determine stress concentrations in laser-hybrid welded butt joints with severe imperfections using 3D scans. For this purpose, a total of 76 specimens were scanned using a high-resolution 3D laser scanner to capture the weld geometry. The scan results were then used to assess the weld quality according to the ISO 12932 standard and to generate numerical models by using the reverse engineering method for 3D finite element (FE) analysis. Additionally, fatigue tests were performed to observe the failure location for each specimen and compare it with the predicted failure location from the FE analysis. While the FE predictions could effectively highlight the critical high-stress regions, they did not consistently match the actual crack initiation sites due to the complexity and variability of weld imperfections. However, considering the micro-support effect through the theory of critical distances improved the accuracy of failure location and fatigue life predictions by accounting for the influence of local stress gradients.