Visualization of interior originating small cracks in high strength titanium alloy and the clarification of very high cycle fatigue mechanisms

2014 Fiscal Year Final Research Report

• Project/Area Number: 24246024
• Research Category: Grant-in-Aid for Scientific Research (A)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Materials/Mechanics of materials
• Research Institution: Hokkaido University
• Principal Investigator: NAKAMURA Takashi 北海道大学, 工学(系)研究科(研究院), 教授 (30237408)
• Co-Investigator(Kenkyū-buntansha): SHIBAYAMA Tamaki 北海道大学, 工学研究院, 准教授 (10241564) ; SHIOZAWA Daiki 神戸大学, 工学研究科, 准教授 (60379336) ; NAKAI Yoshikazu 神戸大学, 工学研究科, 教授 (90155656)
• Co-Investigator(Renkei-kenkyūsha): UESUGI Kentarou 光輝度光科学研究センター, 研究員 (80344399)
• Project Period (FY): 2012-04-01 – 2015-03-31
• Keywords: 疲労 / ギガサイクル疲労 / トモグラフィ / 内部起点型疲労亀裂 / 疲労亀裂進展 / 放射光 / 真空 / チタン合金

Outline of Final Research Achievements

Observations of internal fatigue cracks in Ti alloy were made by using synchrotron radiation micro CT imaging in the large synchrotron radiation facility (SPring-8) .Uniaxial fatigue tests were repeated on the specimen over 1.0E7 cycles, and the growth of the internal fatigue crack was measured by micro CT imaging. To investigate the effects of the environment around internal fatigue crack on crack growth process, the relationship between da/dN and stress intensity factor range were compared with that of surface cracks in vacuum　environment. As a result, internal fatigue crack propagated quite slowly at a rate below 1.0E-10m/cycle. However, the fatigue crack advanced rapidly at a rate of around 1.0E-7m/cycle after reaching at the surface of specimen. Crack growth rate of internal crack agreed quite well with that of surface crack in vacuum. Therefore, vacuum-like environment around internal crack has an important role of fatigue crack process in the very high cycle regime.

Free Research Field

材料強度学