1991 Fiscal Year Final Research Report Summary
Fracture Mechanics Approach for Random Systems and Its Application to Analysis of Strength Depending on Inherent Flaw in Ceramics
| Project/Area Number |
02805013
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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 |
材料力学
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| Research Institution | Tohoku Institute of Technology (1992)
Kyoto University (1990-1991) |
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Principal Investigator |
HOSHIDE Toshihiko Kyoto Univ., Mech. Engng, Assoc. Professor, 工学部, 助教授 (80135623)
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| Co-Investigator(Kenkyū-buntansha) |
INOUE Tatsuo Kyoto Univ., Meach, Engng, Professor, 工学部, 教授 (10025950)
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| Project Period (FY) |
1990 – 1992
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| Keywords | Engineering ceramics / Inherent flaw / Bending strength / Microstruture / Frature toughness / Fracture mechanics / Grain fracture model / Random system |
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| Research Abstract |
There are some problems in evaluating strength of engineering ceramics. The relative strength is observed to be lower than that expected from the fracture toughness criterion with decreasing the flaw size at the fracture origin. At first, such an anomalous behavior of small flaws in ceramics was discussed, based on experimental observations. A concept of the flaw boundary layer was proposed by the interpretation of acoustic emission data. The layer is assumed to be formed around the dominant flaw during loading process, and to be more brittle than the surrounding matrix. Based on the model using the concept of the flaw boundary layer, the simulation of Monte Carlo type was made to explain the anomalous behavior of small flaws. In the relation between the flaw size and the fracture stress, the simulated result showed the same behavior as the experimental observation. However, its physical meaning has not been cleared. At the next stage, a physically acceptable model was established assuming the stable cracking due to the separation per one grain prior to the final unstable fracture. The separation was asslmed to occur when the elastic strain energy stored in one grain just ahead of the tip of fracture zone (crack tip or notch root) exceeds the effective surface energy of single crystal during loading process. Based on the grain fracture model, the simulation was made to explain the abomalous behavior of small flaw, resulting in good correspondence with the experimental observation. As an application to random system, another simulation was also conducted by changing grain-size ahead of the flaw-tip. The result indicated that the scatter in strength was larger decreasing the flaw-size.
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