<p> The Fifth East Asia Symposium of Welding and Joining (5th EAST-WJ), Hokkaido, Japan Appendix 2 – Abstract Submission</p><p>CTOD Toughness correction for laser welded joints with narrow hardened zone 16pt, Arial bold</p><p>Yasuhito TAKASHIMA*, Mitsuru OHATA** and Fumiyoshi MINAMI* 12pt, Arial * Joining and Welding Research Institute Osaka University, 11-1 Mihogaoka, Ibaraki, Osaka, 565-0047, Japan ** Osaka University, 2-1 Yamada-oka, Suita, Osaka, 565-0871, Japan  12pt, Times New Roman italic Email: [email protected]  ( only corresponding author ) </p><p>Extended Abstract 12pt, Arial bold The influences of very narrow weld bead and highly strength overmatching on the fracture toughness of laser beam welded components are investigated. This study focuses on the difference of plastic constraint in fracture toughness specimen (3-point bend specimen, 3PB) and structural components with crack in the weld metal. The equivalent crack tip opening displacement (CTOD) ratio, , for the correction of CTOD toughness for constraint loss in structural components is numerically analyzed. </p><p>The narrowness of weld bead induces constraint loss by plastic deformation in the base metal, both the 3PB and structural components. It is found that the  decrease with very narrow weld metal. The effect of strength mismatch ratio between the weld and base metals on  is rather weak. Therefore, the influence of narrow weld bead on  is important for assessment of fracture performance of laser beam welded component.</p><p>The applicability of  to correction of critical CTOD in laser beam welded components is discussed. The fracture toughness tests with the 3PB and tension panel (edge through-crack panel) of the laser beam welded joints were conducted at a low temperature in the brittle fracture range. It is indicated that  can be applied to the CTOD toughness correction in laser beam welded component. 12pt, Times New Roman</p><p>Keywords (12pt, Arial bold): Laser welds, Fracture toughness, Strength mismatch, Constraint loss, Weibull stress 12pt, Times New Roman</p>