| Project/Area Number |
06650726
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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 |
Physical properties of metals
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
NARITA Nobutaka Kyoto Univ., Graduate School of Eng.Assoc.Prof., 工学研究科, 助教授 (10026213)
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| Project Period (FY) |
1994 – 1995
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| Project Status |
Completed (Fiscal Year 1995)
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| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1995: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1994: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Keywords | Crack / Crystal defect / Dislocation / Fracture toughness / Embrittlement / Fracture |
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| Research Abstract |
Interactions of a crack with mobile defects such as dislocations and interstitial impurities were investigated with particular attention to the effect of defect redistribution on crack extension. The fracture toughness K_<IC> in NaCl crystals is gradually decreased with increasing temperature in the range below room temperature. At above room temperature, The values of K_<IC> are increased with increasing temperature. Computer aimulation showed that at low temperatures anti-shielding dislocations generated from internal sources are more active and serve to decrease K_<IC> values with increasing temperature, while at high temperatures shielding dislocations are much emitted from a crack tip by thermal activation and cause to increase K_<IC> values. This tendenccy is consistent with the observed dependence of K_<IC> values, but there are some quantitative differences between computed and experimental results. Photo-elastic observations showed that those differences are caused by crack tip blunting as well as the stabilization of dislocation structures. In case of mobile interstitial impurities in iron alloy crystals, the impurities distributed ahead of a crack tip intensify the local k field to promote crack extension so as to decrease K_<IC> values. The forward impurity distribution is enhanced by the tetragonal strain of impurity atoms and also by the mutual interaction of impurities under the presence of a crack. The promotion of crack extension by mobile impurities was verified using the plasma charging of impurities into Fe-Si alloy crystals.
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