Maintenance of fatigue damaged friction stir welding joints by laser peening and integrity evaluation with synchrotron radiation laminography

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K06761
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Composite materials/Surface and interface engineering
• Research Institution: Okinawa National College of Technology
• Principal Investigator: MASAKI Kiyotaka 沖縄工業高等専門学校, 機械システム工学科, 准教授 (30323885)
• Research Collaborator: SANO yuji ; SANO tomokazu ; KAJIWARA kentarou ; OMAR Hatamleh
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 摩擦攪拌接合 / 疲労き裂進展 / 放射光ラミノグラフィ / レーザピーニング

Outline of Final Research Achievements

In this study, in order to ensure integrity of fatigue damaged friction stir welded (FSW) joints of 3mm thickness which has a fatigue crack at center part of welding center, two types of laser peening treatment are applied at the tip of the fatigue crack. One is conventional LPwC treatment treated in water and the other one is newly developed Dry-LP treatment treated in atmosphere. When the Dry-LP was applied, crack growth was almost suppressed including the inside of the specimen. However, when the LPwC was applied, fatigue crack propagate about 1 mm during 2.0x104 cycles and its fatigue crack propagation rate had accelerated. This study suggested that Dry-LP is suitable for FSWed thin plate. In addition, as a result of simultaneously visualizing the stirred structure formed by FSW process and the fatigue crack using synchrotron radiation laminography, it became clear that the fatigue crack propagates in the boundary portion of the stirred structure and the base material.

Free Research Field

材料力学

Academic Significance and Societal Importance of the Research Achievements

本研究では、摩擦攪拌（FSW）継手材を対象として、放射光ラミノグラフィを利用した疲労き裂と摩擦攪拌組織の同時可視化をおこない、世界で初めてFSW継手材に発生した疲労き裂進展状況と摩擦攪拌組織を可視化した。この成果は、FSW継手のき裂発生・進展メカニズム解明に大きく貢献するものである。さらに、疲労損傷を受けたFSW継手材にレーザピーニング（LP）処理を施し、特にDry-LP処理によって疲労き裂の成長を停止させた成果は、航空機などの薄板構造物の安全性を確保することにつながり、社会的に大きな意義を持つものである。