1990 Fiscal Year Final Research Report Summary
Fracture Mechanics- and Image Processing-Aided Assessment of Fatigue and Fracture Toughness of Austempered Ductile Cast Iron
| Project/Area Number |
01550060
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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 |
機械材料工学
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| Research Institution | Department of Mechanical Engineering, Faculty of Engineering, Kyushu Institute of Technology |
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Principal Investigator |
HARADA Shoji Prof. Dept. Mech. Engng, Kyushu Institute of Technology, 工学部・設計生産工学科, 教授 (80029199)
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| Co-Investigator(Kenkyū-buntansha) |
FUKUSHIMA Yoshihiro Research Assistant, Dept. Mech. Engng, Kyushu Inst. Techn, 工学部・設計生産工学科, 助手 (40156774)
AKINIWA Yoshiaki Associate Prof. Dept. Mech. Engng, Kyushu Inst. Techn, 工学部・設計生産工学科, 助教授 (00212431)
NODA Nao-aki Associate Prof. Dept. Mech. Engng, Kyushu. Inst. Techn, 工学部・設計生産工学科, 助教授 (40172796)
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| Project Period (FY) |
1989 – 1990
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| Keywords | Ductile Cast Iron / Low-Cycle Fatigue / Spheroidal Graphite and Matrix / Laser Interferometric Gauge / Crack Initiation and Propagation / Fracture Mechanics / Crack Closure / Bainite, Ferrite and Pearlite Matrix |
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| Research Abstract |
To examine quantitatively the effects of spheroidal graphite and matrix on strength of ductile cast iron, low-cycle fatigue tests were mainly conducted. Three kinds of ductile cast irons, ferritic, pearlitic and bainitic ductile irons with same chemical composition were prepared by heat treatment. First, graphite morphology such as nodule count, nodularity, area fraction etc. of each material was measured by an image processing analyzer. Then, a laser interometric measuring instrument for measuring closure behavior of a spheroidal graphite-initiated small crack with a higher accuracy was newly developed.
Through the fatigue tests, it was found that the matrix structure primarily controls the fatigue strength and that the spheroidal graphite plays an important role during the fatigue process from microcrack initiation to final failure. In cases of bainitic and pearlitic materials, a microshrinkage formed during fabrication in the matrix was found to be responsible for the crack initiation site. Finally, the results of macroscopic crack propagation tests revealed that the matrix structure hardly influences the macroscopic crack propagation rate.
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