| Project/Area Number |
60550058
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
材料力学
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| Research Institution | University of Tsukuba |
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Principal Investigator |
KOTERAZAWA Ryoichi Institute of Engineering Mechanics, University of Tsukuba, 構造工学系, 教授 (80029397)
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| Project Period (FY) |
1985 – 1986
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| Project Status |
Completed (Fiscal Year 1986)
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| Budget Amount *help |
¥1,800,000 (Direct Cost: ¥1,800,000)
Fiscal Year 1986: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1985: ¥1,300,000 (Direct Cost: ¥1,300,000)
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| Keywords | Fatigue / Creep / Fracture mechanics / Fractography / Variable stress |
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| Research Abstract |
Fatigue and creep crack propagation studies were carried out under variable stress conditions where overstresses of a very small number of cycles(1--2cycles) or of very short time( <about> 10sec) were applied intermittently between understress below the threshold of a large number of cycles (more than <10^5> cycles) or of long time( <about> 10hr).
In the case of fatigue crack propagation at room temperature, Propagation rates were accelerated significantly (more than one hundred times in some cases) by such variable stresses as compared with the case of steady cyclic stresses both in air and in inert gas(nitrogen) environment. When magnitude of the understress is low, the acceleration was less in air than in nitrogen gas. This is shown to be a result of crack closure due to oxidation of fracture surface by means of Auger electron spectroscopy.
In the case of creep crack propagation at elevated temperature, the acceleration by variable stresses was considerably less in thick plate specimens than in thin plate specimens, indicating an important effect of the deformation in thickness direction on the acceleration.
In the case of creep-fatigue crack propagation under alternating stresses at elevated temperature, it was shown that the crack propagation is correleted well in terms of <DELTA> J both in air and in vacuum. The propagation rates in vacuum were slightly less than those in air due to absence of oxidation.
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