Effect of Line Weld Angle on Fatigue Properties of Crossed Laser Spot Welding Joints

This study investigates the e ff ect of the line weld angle with respect to the load axis on the strength properties of cross-type LSW joints with four line welds. Static and fatigue tests, fi nite element method analysis, and three-dimensional crack observation were performed on joints with line welds at three di ff erent angles 30 degrees, 45 degrees, and 60 degrees, respectively to investigate the e ff ect of the line weld angle. As a result, the cross-type LSW joints showed superior strength properties compared with those of the 0-type LSW joints regardless of the line welding angle. The fatigue strength was particularly superior in the region with a high test force amplitude. The amount of fatigue crack propagation in the thickness direction increases as the line welding angle increases. This trend is similar to that observed for the 0-type joints reported by Sannomiya et al. It can be inferred that an increase in the amount of crack propagation in the thickness direction increases the crack propagation path length, and thus the crack propagation life. Furthermore, FEM analysis showed that the line weld angle does not signi fi cantly a ff ect the fatigue crack initiation life. The results of three-dimensional observations showed that too large a line welding angle increased the number of crack initiation points and reduced the crack growth life relative to the total life, resulting in a signi fi cantly shorter crack growth life compared with the fracture life. These results indicate that the strength properties of LSW joints can be improved by increasing the number of line welds, and that further strength improvement can be expected by welding line welds at the appropriate angles with respect to the load axis. For the conditions considered in this study, the line welding angle that exhibits the highest fatigue strength is estimated to be between 45 degrees and 60 degrees.