1. Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka Prefecture 565-0871, Japan
2. Kobe Steel, Ltd., 100-1 Miyamae, Fujisawa, Kanagawa Prefecture 251-8551, Japan
3. Joining and Welding Research Institute, Osaka University, 11-1 Mihogaoka, Ibaraki, Osaka Prefecture 567-0047, Japan