Study on Reduction of Residual Stress of Welding Joint Using Vibration

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Welding is widely used for construction of many structures. There exists residual stress near the bead because of locally given heat. Tensile residual stress on the surface degrades strength for cumulative damage. Some reduction methods of residual stress were presented. In this paper, a new method is proposed in which vibrational load is used during welding operation and an analytical method for the proposed method is presented. Advantage of this method is that vibrational load is generated by a small shaker. This method is expected to be a practical one.First, reduction of residual stress is examined experimentally. Two plates of 100mm width are used. Two plates of rolled steel for general use (JIS SS400) are supported on the supporting devices by bolts and shaken by a small shaker during welding. Specimens are butt welded using automatic CO_2 gas shielded arc welding machine. Groove is V-shaped. Welding is completed through one pass. Excitation frequency is chosen as 60Hz which is t … More he fundamantal natural frequency of specimens before welding. In order to examine reduction effect of residual stress at non-resonane frequency, excitation frequency is also chosen as 100Hz. Residual stress is measured by removing the quenched scale chemically and using a parelelled beam X-ray diffractometer with a scintillation counter.From the experiment, it is found that on the bead, tensile residual stress is significantly reduced when vibrational load is acting during welding. At points near the bead, residual stress is also reduced. At points far from the bead, compressive residual stress tends to be tensile. Residual stress decreases as the amplitude of excitation increases.Next, an analytical method for reduction of residual stress by the proposed method is examined. It is obvious that reduction of residual stress is caused by local plastic deformation because initial residual stress is great and nearly equal to yielding stress. Thus, an analytical model which consists of mass and preloaded spring with elasto-plastic characteristic is used. From the analysis, it is found that reduction rate of residual stress increases as the amplitude of excitation increases. Thus, effectiveness of the proposed method can be demonstraited by experimnet and analysis. Less