1999 Fiscal Year Final Research Report Summary
Mechanism of the emission of shielding dislocations from a crack tip
| Project/Area Number |
10650652
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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 |
Physical properties of metals
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| Research Institution | Kyushu Institute of Technology |
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Principal Investigator |
NARITA Nobutaka Faculty of Engineering, Kyushu Institute of Technology, Professor, 工学部, 教授 (10026213)
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| Co-Investigator(Kenkyū-buntansha) |
TAKAHARA Yoshihiro Faculty of Engineering, Kyushu Institute of Technology, Instructor, 工学部, 助手 (50163308)
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| Project Period (FY) |
1998 – 1999
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| Keywords | fracture / fracture toughness / dislocation / crack / stress shielding / lattice defect / ionic crystal / semiconductor |
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| Research Abstract |
In this research project, the mechanism of dislocation emission from a crack tip in MgO, NaCl and Si crystals have been studied using microscopic techniques of a electron microscope and an atomic force microscope. The results obtained are summarized as in the following.
(1) In thick crystals, hinge-type structures of slip bands are formed around a crack tip, while in thin crystals dislocation structures are observed on slip planes intersecting through a crack tip line.
(2) Dislocations are emitted from a crack tip through the nucleation of half-loop dislocations, and in thin crystals, the half-loop dislocations are generated at the intersection of a crack tip to free surface as well as at a crack jog and kink.
(3) Dislocations are introduced not only ahead of a crack tip, but also formed behind a crack tip.
(4) The sign of dislocations emitted ahead of crack tip is opposite to that of dislocations behind a crack tip, when they are lying on the same slip plane.
(5) In any cases, dislocations which shield the crack stress field from an applied stress are mostly emitted from a crack tip.
(6) In the deformation of NaCl crystals at high temperature, microscopic cross slip takes place on indefinite planes, so that half-loop dislocations can be expanded along a crack tip line by the cross slip to shield all over the crack front, leading to the suppression of crack growth.
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Research Products
(8 results)
