2002 Fiscal Year Final Research Report Summary
Collective Mechanical Behavior of dislocation Network Developed under Indentation
| Project/Area Number |
13450047
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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 |
SHIBUTANI Yoji Osaka Univ., Graduate School of Eng., Prof., 大学院・工学研究科, 教授 (70206150)
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| Co-Investigator(Kenkyū-buntansha) |
HIGASHIDA Kenji Kyushu Univ., Graduate School of Eng., Asso. Prof., 大学院・工学研究科, 助教授 (70156561)
KOYAMA Atsuhiro Osaka Univ., Graduate School of Eng., Research Associate, 大学院・工学研究科, 助手 (40324800)
OGATA Shigenobu Osaka Univ., Graduate School of Eng., Assis. Prof., 大学院・工学研究科, 講師 (20273584)
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| Project Period (FY) |
2001 – 2002
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| Keywords | Nanoindentation / Dislocation emission / Collective mechanics / Focus ion beam technique / Molecular Dynamics / Discrete dislocation / Multiscale modeling |
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| Research Abstract |
Cross sections of the indent-induced plastic zones is single crystalline silicon and aluminum are observed by the transmission electron microscopy (TEM) in order to know their internal structural changes under indentation. A tiny piece involving the indented region is cut from the sample and thinned until a few hundred nanometer thickness by means of the Focus Ion Beam (FIB) technique. At the case of silicon, the hydrostatic pressure-induced phase transition recovers to the diamond structure with the different crystallographic orientation from the bulk after unloading, being compared with the sample having received the heat treatment for recrystallization. Perfect dislocations consisting of the 60 degree dislocations and screw dislocations may be emitted from the boundary between the phase transition and the diamond bulk. Emission and movemeat mechanism of the dislocation are also investigated with help of the molecular dynamics simulations. On the other hand, it is found at the case o
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f single crystalline aluminum that the subgrains less than one micron are organized at the maximum shear stress region. It seems to be one of the self-organization of dislocation network as a result of the collective mechanical behaviors.
New finding of unstable displacement burst observed in the relation between the indent load and indent depth of a nanoindentation test is much possible to be related to dislocation emission. In the present research, the dislocation emission and the prismatic dislocation loop formation in a single crystalline aluminum are simulated by the molecular dynamics. Effects of the stress distribution due to two different types of indenters and of the interatomic description by three different embedded atom type potentials are discussed with much emphasis. At a result, the dislocations are emitted from the severely damaged surface atomic layer due to the indenter and the prismatic dislocation loops, which have the same gliding direction but not on the glide plane, are attained by unstable reaction between the shear loops emitted from the surface and cross slip mechanism. Less
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