A method for improving the fatigue strength of thin steel sheet gas metal arc (GMA) welded joints using weaving welding was evaluated. Weaving created peaks and valleys at the weld toe. The valley has high stress triaxiality, and plastic deformation is unlikely to occur. Fatigue cracks occurred from the peaks with gentle toe shapes. Therefore, it is considered that the fatigue strength is improved by reducing the initiation points of the crack and stress concentration at the toe. The fatigue test results showed that the fatigue limit of the weaving welding joint was improved compared with that of the normal welding joint.Furthermore, the optimal weaving condition, which is the relationship between the weaving wavelength and torch swing amplitude, was evaluated. As a consequence, when the wave density is small, the crack initiation point is not restricted to the peak. On the other hand, when the wave density is large, the peak and valley shapes merge and the weaving effect disappears.In addition, undercuts occurred when the swing amplitude became too large. The mechanism of improving the fatigue strength was considered by observing the initiation point of the fatigue microcracks.

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