Bending Fatigue Characteristics of Butt Joints by Laser-Arc Hybrid Welding for Steel Bridge Members

To investigate the application of laser-arc hybrid welding to manufacturing steel bridge members, a series of experiments were carried out. One-pass full-penetration butt joints employing steels for bridge high-performance structures (SBHS500) were fabricated by the laser-arc hybrid welding with a thickness of 15 mm, which applied the specified welding condition based on the previous study to avoid generating cracks and defects. Subsequently, the same dimensional arc welded butt joints utilizing SBHS500 were fabricated. The four-point bending fatigue tests were conducted on the laser-arc hybrid welded butt joints and arc welded butt ones. In order to elucidate the bending fatigue characteristics of butt joints fabricated by the laser-arc hybrid welding, the fatigue strength of laser-arc hybrid welded butt joints were compared with that of arc welded butt joints. The experimental results revealed that the laser-arc hybrid welded butt joints had the same or higher fatigue strength than the arc welded butt joints under the stress range of 250 MPa or more, and no cracks were observed under the stress range of 200 MPa. The fatigue strength of the butt joints using laser-arc hybrid welding was improved compared with those using conventional arc welding, possibly because the hardening due to the rapid heating and cooling around the weld toe in laser-arc hybrid welded butt joints was larger than that in arc welded butt joints.