| Project/Area Number |
09650108
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Materials/Mechanics of materials
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| Research Institution | OITA UNIVERSITY |
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Principal Investigator |
GOTO Masahiro OITA UNIVERSITY,PRODUCTION SYSTEMS ENGINEERING,ASSOCIATE PROFESSOR, 工学部, 助教授 (30170468)
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| Co-Investigator(Kenkyū-buntansha) |
IMADO Keiji OITA UNIVERSITY,PRODUCTION SYSTEMS ENGINEERING,RESEARCH ASSOCIATE, 工学部, 助手 (80160050)
YAMAMOTO Takaei OITA UNIVERSITY,PRODUCTION SYSTEMS ENGINEERING,RESEARCH ASSOCIATE, 工学部, 助手 (20295166)
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| Project Period (FY) |
1997 – 1998
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| Project Status |
Completed (Fiscal Year 1998)
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| Budget Amount *help |
¥2,000,000 (Direct Cost: ¥2,000,000)
Fiscal Year 1998: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1997: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Keywords | FATIGUE / Al ALLOY / CARBON STEEL / CRACK INITIATION / ATOMOSPHERE / STATISTICAL TREATMENT / CRACK PROPAGATION / PLAIN SPECIMEN / AI合金 / 微小き裂伝ぱ |
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| Research Abstract |
Rotating bending fatigue tests of the smooth specimens were carried out in room air using a normalized 0.37 % carbon steel and an age hardened aluminum alloy 7075-T6. In order to clarify the effect of air conditions on the fatigue damage, both the temperature and humidity of laboratory air were changed for each test. Air conditions used in the tests were moist air (relative humidity h = 70-80%) at 20ﾟC, moist air at 35ﾟC and dry air (h = 35-45%) at 35ﾟC.The main results of fatigue behavior in each atmosphere may be summarized as follows :
1. The S-N curve is influenced by the atmosphere. The fatigue life of steel at 20ﾟC is longer than at 35ﾟC, while the effect of humidity is negligible. However, the fatigue life of Al alloy is longer in dry air than moist air.
2. The crack initiation life of steel is longer for 20ﾟC than 35ﾟC, however the difference in humidity does not affect the crack initiation life. On the other hand, crack initiation life of Al alloy is strongly affected by the humidity than temperature and it is longer in dry than moist air.
For both the metals, the growth rate of a surface crack is lower in moist air compared with dry air, as the growth rate approaches the threshold level. The retarded growth rates in moist air may result from the formation of fretting oxides. For cracks with dl/dN in excess of 10^6 mm/cycle, humidity does not influence the growth behavior. The temperature also affects the crack growth rate, but this effect is not large.
3. The crack initiation life, growth life and fatigue life distribution is represented by Weibull distribution. The statistical distribution of crack growth rate is expressed by both a log-normal and a Weibull distribution function. No significant difference in the CV, the coefficient of variation, versus 1 relationship is observed due to a difference in laboratory airs.
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