1993 Fiscal Year Final Research Report Summary
Local Crack-Tip Process and Its Effect on Fracture Toughness
| Project/Area Number |
03452245
|
|---|
| Research Category |
Grant-in-Aid for General Scientific Research (B)
|
| Allocation Type | Single-year Grants |
|---|
| Research Field |
Physical properties of metals
|
|---|
| Research Institution | KYOTO UNIVERSITY |
|---|
Principal Investigator |
NARITA Nobutaka Kyoto Univ., Dept.of Metallurgy, Assoc.Prof., 工学部, 助教授 (10026213)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
ADACHI Hiroshiko Kyoto Univ., Dept.of Metallurgy, Assoc.Professor, 工学部, 教授 (60029105)
|
|---|
| Project Period (FY) |
1991 – 1993
|
| Keywords | Fracture / Crack / Dislocation / Crystal defect / Fracture toughness / Intersticial impurity / Embrittlement |
|---|
| Research Abstract |
Local activities of crystal defects such as dislocations and mobile impurities near a crack tip were investigated with particular attention to the shielding/anti-shielding effects on fracture toughness. The fracture toughness, K_<IC>, in ionic crystal such as NaCl is decreased with increasing temperature in the range between 77 and 300K.The change of the K_<IC> is opposite to that at high temperatures where K_<IC> values increase with increasing temperature. Computer simulation showed that, in the low temperature range, anti-shielding dislocations generated from intenal 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 contribute to the increase of K_<IC> values. A comutation of electron states suggested that the chemical adsorption of water molecules in ionic crystals promote the dislocation generation from the surface and may lower the temperature of brittle-ductile transition. In case of mobil interstitial impurities in metallic crystals such as iron, the impurities concentrate neara crack tip to intensify the local k field at the tip, indicating the anti-shielding effect due to impurities. The intensification of the crack-tip field promotes the crack extension so as to decrease K_<IC> values. The anti-shielding effect by impurities was verified using Fe-Si alloy crystals charged with light inert-gas elements such as helium.
|
