Welding is widely used for constructing of many structures. Residual stress is generated near the bead because metal near the bead is heated. Tensile residual stress degrades fatigue strength. Several methods of reducing of residual stress are developed. Heat treatment and shot peening are practically used. These methods are time-consuming and require special devices. In this study, a new method of reducing residual stress is proposed. In this method, vibrations are used during welding, namely, ultrasonic vibration and low-frequency vibration. The effectiveness of the method is examined experimentally. It is concluded that tensile residual stress is reduced when ultrasonic vibration or low-frequency vibration is used. When ultrasonic vibration and low-frequency vibration are used simultaneously, the reduction rate of residual stress is large. Results of the experiment are examined by simulation qualitatively. The yield stress immediately after welding is very low because the temperature of the metal near the bead is very high. Then, an analytical model considering the yield of metal is proposed. From the simulation method, results of the experiment are demonstrated qualitatively.
