2022 年 63 巻 4 号 p. 570-578
In this study, to clarify the weld area shape that achieves excellent fatigue properties in laser welded joints, an ϕ-shaped weld, which is a combination of a circular weld and a linear weld, was selected for evaluation. Joints with a linear weld having three different linear weld angles with respect to the load axis were fabricated and fatigue tests were conducted. The results showed that the effect of the linear weld angle was remarkable in a relatively high loading amplitude range, and the fatigue life increased as the angle increased. In addition, three-dimensional observation of fatigue cracks was carried out to investigate the fracture mechanism and the factors causing the difference in fatigue strength. It was clarified that the crack propagation life is increased because the crack propagates in the thickness direction not only at circular weld area but also at the linear weld area, when the linear weld angle respecting to loading direction are 45°, 90°. Furthermore, three-dimensional FEM analysis was carried out to recognize the stresses field around the linear weld area. It was clarified that the stresses around the weld area were distributed as the linear weld angle increased, which delayed crack initiation, leading to excellent fatigue properties. Therefore, the fatigue life in the high test-force amplitude region can be improved by providing a weld area shape that distributes the stress and allows the crack to propagate in the thickness direction.
