Development of a method for significantly improving the fatigue life of welded joints by the laser processing

2022 Fiscal Year Final Research Report

• Project/Area Number: 20H02372
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 24020:Marine engineering-related
• Research Institution: Kyushu University
• Principal Investigator: Gotoh Koji 九州大学, 工学研究院, 教授 (60274487)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 疲労 / 特殊加工 / 溶接 / 構造・材料 / 維持管理工学

Outline of Final Research Achievements

Topics (1) to (3) that could be introduced during the construction stage to improve the fatigue performance of large welded structures such as ships, offshore structures, bridges and steel structures of high-rise buildings were studied.
(1) Suppression of crack propagation by localised laser irradiation to refine the base metal grains; (2) Suppression of fatigue crack initiation by hardening the crack initiation surface area by carburization; and (3) Expansion of the range of application (welding position) of laser-arc hybrid welding that can achieve secondary stress suppression due to weld deformation.

Free Research Field

溶接構造物の疲労及び破壊強度評価，溶接及び熱切断技術を中心とする大型溶接構造物の建造技術

Academic Significance and Societal Importance of the Research Achievements

溶接構造物の高サイクル疲労強度への主な影響因子は亀裂発生領域近傍の応力集中であるが，溶接により構造体を製作する以上これを回避することは難しい．本研究は建造本来の道具として導入する大出力レーザを，溶接止端部近傍の硬化や結晶粒微細化という疲労寿命改善効果が期待される複数の対策に活用することを考えた結果，応力集中場の生成が避けられなくとも大幅な寿命改善を達成した点が学術的かつ社会的に高い意義を有している．また，本研究で基礎知見を得た手法を用いれば，社会インフラである大型溶接構造体の寿命を大きく改善できるため，これに要する費用の削減が可能となる．