| Project/Area Number |
08455053
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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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 | THE UNIVERSITY OF TOKYO |
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Principal Investigator |
SAKAI Shinsuke THE UNIVERSITY OF TOKYO,SCHOLL OF ENGINEERING,PROFESSOR, 大学院・工学系研究科, 教授 (80134469)
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| Co-Investigator(Kenkyū-buntansha) |
TAKANO Tacho THE UNIVERSITY OF TOKYO,SCHOLL OF ENGINEERING,ASSITANT, 大学院・工学系研究科, 助手 (10010852)
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| Project Period (FY) |
1996 – 1997
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| Project Status |
Completed (Fiscal Year 1997)
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| Budget Amount *help |
¥7,700,000 (Direct Cost: ¥7,700,000)
Fiscal Year 1997: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 1996: ¥6,500,000 (Direct Cost: ¥6,500,000)
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| Keywords | RESIDUAL STRESS / FATIGUE STRENGTH / STAINLESS / LASER / PREVENTION OF FATIGUE / SN-DAIGRAM |
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| Research Abstract |
This research investigates the possibility of improvement of fatigue strength using the laser irradiation under the condition the melting or the variation of micro structure of metal does not start. Used metal is SUS304. As a result, it is clarified that the improvement of fatigue strength is achievable if appropriate conditions are satisfied. On irradiating laser on the surface of metals, two major factor that influence the fatigue strength exist : 1. Residual stress due to thermal stress, 2. Rough geometry formed on the surface of metals. Residual stress is given by only plastic deformation due to thermal stress below the temperature that provokes the variation of micro structure of metals. Firstly, by the analysis using non-stationary elastic-plastic finite element analysis, it is shown that the distribution of residual stress greatly depends on the geometry of test specimen. Secondly, by observation using electron microscope, it is clarified that the roughness of metal surface is r
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elated to the oxidation film formed by the irradiation of laser. In this case, many cracks appear of the surface and so the fatigue strength is reduced. If the laser is irradiated on circular bar type specimen, the compressive residual stress remains on the surface and so the improvement of fatigue strength is expected. In fact, the fatigue strength is unexpectedly reduced if the compressive residual stress is accompanied by the surface roughness. However, if the state of compressive residual stress not accompanied with surface roughness is attained, the fatigue strength is expected to be improved. It is shown that these conditions are achieved if the laser is irradiated near the notched portion of circular bar specimen from the analysis using finite element analysis. This derived theory is confirmed experimentally using notched circular bar specimen. The fatigue strength for laser irradiated specimen is surely improved compared with that for non-irradiated one. This prinsiple is expected to be applied widely in the future. Less
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