Elucidation of short crack propagation mechanism in ultra low carbon lath martensite

2021 Fiscal Year Final Research Report

• Project/Area Number: 20K22468
• Research Category: Grant-in-Aid for Research Activity Start-up
• Allocation Type: Multi-year Fund
• Review Section: 0401:Materials engineering, chemical engineering, and related fields
• Research Institution: Shimane University
• Principal Investigator: Ueki Shohei 島根大学, 学術研究院理工学系, 助教 (50880382)
• Project Period (FY): 2020-09-11 – 2022-03-31
• Keywords: ラスマルテンサイト / き裂 / 転位

Outline of Final Research Achievements

In this study, the dislocation motion near the crack tip was directly observed using a transmission electron microscopy and associated with microstructurally fatigue crack propagation of lath martensite steel to clarify the crack propagation mechanism. In-situ observation of dislocation motion revealed that the activation of pre-existing dislocations ahead of the crack tip occurred prior to the dislocation emission from the crack tip. When the applied load reached a level at which the dislocation emission from crack tip occurred, the activity of pre-existing dislocations became remarkable, and the dislocations were tangled with each other. These findings suggest that the dislocation cell structure, which plays an important role in the fatigue crack propagation of lath martensite, is formed by the activation and tangle of pre-existing dislocations ahead of the crack tip.

Free Research Field

疲労き裂進展

Academic Significance and Societal Importance of the Research Achievements

本研究では、透過型電子顕微鏡を用いてラスマルテンサイト鋼のき裂先端における転位運動を直接観察し、先行研究で報告されているブロック内き裂進展と対応付けることで、き裂進展機構の理解を深めることに成功した。さらに、透過型電子顕微鏡内で引張荷重を負荷する試験片の観察領域に、所望の結晶方位を有する組織を配置する手法の確立に成功し、その応用範囲はきわめて広い。本研究で得られた成果は、き裂先端近傍の塑性変形挙動をトランススケールで理解し、き裂進展機構の解明に貢献する重要な知見を提供するものである。