Abstract
Welding is widely used for construction of many structures. Residual stress is generated near the bead because of locally given heat. Tensile residual stress degrades strength of structure. The authors have proposed a reduction method for residual stress using vibration during welding and applied to welding of thin plates. Residual stress is more reduced when larger amplitude of vibration is used. In this paper, repair welding of mold is considered and surface of a thick plate is welded. Two ultrasonic vibrations are used to get large amplitude and reduction of residual stress is examined. Residual stress is more reduced than using one ultrasonic vibration. It is well known fact that residual stresses are statistically distributed. 3 specimens are made for the same condition. Using experimental data, distribution of residual stresses is evaluated by analysis of variance. It is found that difference of distribution of residual stress of each specimen and those of all specimens is small. By t test, it is demonstrated that the method using two ultrasonic vibrations is more effective than that using one ultrasonic vibration for reduction of residual stress.
