Reduction of Residual Stress of Welded Joint Using Vibrational Load

摘要

Welding is widely used for construction of many structures. Since welding is a process using locally given heat, residual stress is generated near the bead. Tensile residual stress degrades fatigue strength. Some reduction methods of residual stress are presented and, for example, heat treatment and shot peening are practically used. However, those methods need special tools and are time consuming. In this paper, a new method for reduction of residual stress using vibrational load during welding is proposed. The proposed method is examined experimentally for some conditions. Two thin plates are supported on the supporting device and butt-welded using an automatic CO_2 gas shielded arc welding machine. Residual stress in the direction of the bead is measured by using a paralleled beam X-ray diffxactometer with scintillation counter after removing quenched scale chemically. First, residual stress for one pass welding for some excitation frequencies is examined. Material of specimen is rolled steel for general structure (JIS400). In this case, excitation frequencies are selected as the natural frequency and higher frequency. For both frequencies, tensile residual stress near the bead is significantly reduced. Second, residual stress for two pass welding for some excitation frequencies is examined. Specimens are welded at one side and then at reverse side. In this case, some frequencies are selected. For all frequencies, tensile residual stress near the bead is reduced at both sides of specimen. Finally, the proposed method is applied to the specimen made of high tensile strength steel. In this case, tensile residual stress near the bead is also reduced.