1997 Fiscal Year Final Research Report Summary
Unified Study on Brittle-Ductile Transition Based on Atomistic Point of View
| Project/Area Number |
08455061
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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 | Osaka University |
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Principal Investigator |
KITAGAWA Hiroshi Osaka University, Department of Mechanical Engineering, Professor, 工学部, 教授 (30029095)
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| Co-Investigator(Kenkyū-buntansha) |
OGATA Shigenobu Osaka University, Department of Mechanical Engineering, Research Assistant, 工学部, 助手 (20273584)
NAKATANI Akihiro Osaka University, Department of Mechanical Engineering, Associate Professor, 工学部, 助教授 (50252606)
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| Project Period (FY) |
1996 – 1997
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| Keywords | Materials Strength / Brittle-Ductile Transition / Molecular Dynamics / Atomic Force Microscope / Ceramics / Micro-Indentation / Interaction of Cracks / Grain Boundary Deformation Mechanism / 微小硬度 |
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| Research Abstract |
Brittle-ductile transition (BDT) was studied on the basis of atomistic pioint of view, special attention being focused on mobility of localized deformation mechanism. Main results obtained are as follows :
(1) As fracture of the material is regarded as release or relaxation process of energy which is brought from the external source, BDT is to have strong dependence on the magnitude of the energy and extend of deformed area. Concretely ;
a) Experimental results of micro-indentation test for SiC-single crystal and SiN polycrystal show that BDT appearing in highly-brittle materials seems to be a relaxation process due to mutual interaction of micro-cracks.
b) Interaction analysis between a macro crack and micro ones by homogenization method shows the stress intensity factor around the macro crack is larger than the micro, which means coalescence of the micro-cracks brings about BDT in the above case.
c) Stress shielding effect due to dislocation structure which is formed in near crack-tip field is important characteristics for BDT in ductile matallic crystal, which has been concluded after a discrete dislocation analysis.
d) From a molecular dynamics analysis of crack propagation in an amorphous metallic material, there exists no hardening mechanism of localized deformation, which in turn brittle fracture occurs macroscopically in spite of ductile rearrangement of atomic structure in micro-scale.
(2) A first-principle analysis on strength properties on Al-grain boundary indicates Si impurity decreases the strength drastically. And from same analysis for AIN-Al grain boundary, distribution of electron density indicates that physical (not chemical) property dominates in the bonding of this interface and then, fracture occurs in Al side near the boundary.
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