2001 Fiscal Year Final Research Report Summary
Nondestructive Observation of Dislocation Structure using ECCI Method and Embryology of Fatigue Cracks.
| Project/Area Number |
12450284
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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 |
Structural/Functional materials
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| Research Institution | Osaka City University |
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Principal Investigator |
HASHIMOTO Satoshi Osaka City University, Department of Intelligent Materials Engineering, Professor, 大学院・工学研究科, 教授 (50127122)
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| Co-Investigator(Kenkyū-buntansha) |
MIMAKI Takuro Doshisha University, Department of Mechanical Engineering, 工学部, 教授 (20066244)
KANEKO Yoshihisa Osaka City University, Department of Intelligent Materials Engineering, Lecturer, 大学院・工学研究科, 講師 (40283098)
VINOGRADOV Alexei Osaka City University, Department of Intelligent Materials Engineering, Associate Professor, 大学院・工学研究科, 助教授 (10283102)
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| Project Period (FY) |
2000 – 2001
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| Keywords | Fatigue / ECCI Method / Dislocation Structure / PSB / Single Crystal / Nondestructive Observation |
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| Research Abstract |
Intragranular fatigue cracks are initiated frequently along the persistent slip bands (PSBs) at which cyclic plastic strains are localized. Dislocation structure of the PSB is characterized by a ladder-like structure which consists of dislocation wall and channel. Hence, by detecting this ladder-like dislocation structure, we can predict the fatigue crack initiation. However, a material must be shaped to a thin foil in order to observe the dislocation structure using a conventional TEM. In the present research project, we make attempt to perform nondestructive dislocation observation using Electron Channelling Contrast Imaging (ECCI) method, with a view to predicting the fatigue cracking.
Copper single crystals having defined stress axes were prepared by the Bridgman method. The copper single crystals were cyclically deformed at a constant plastic strain amplitude γ_<p1>=2x10^<-3> until various numbers of cycles. Surfaces of the fatigued single crystals were observed by the ECCI method.
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During the cyclic deformation tests, we recorded shapes of hysteresis loops and calculated the Bauschinger energy parameter β_E from the hysteresis loop shape. It has been proposed that the β_E value became a local maximum when the PSBs begin to develop. In the single crystal having [123] tensile axis, the β_E value became a local maximum at 1200 cycle. The ECCI observations after 1500 cycles revealed band-like contrasts along a primary slip plane. On the other hand, no characteristic contrast could be detected at the ECCI observation at 500 cycles. When we observed the band-like contrast at a high magnification, the ladder-like dislocation structure where the wall spacing was about 1.4 μm. Being very similar to the PSB observed using the TEM, the observed band-like contrast must be the PSB structure in the vicinity of specimen surface. At the single crystal having [001] tensile axis, grid-like contrast was detected in the ECCI observation. It is likely that this contrast is attributed to the labyrinth dislocation structure which has been reported in TEM observation at the [001] tensile axis.
From the abovementioned observations, we can suggest that the prediction of fatigue cracking is possible by detecting the PSB structure using the nondestructive ECCI observation. Less
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