2004 Fiscal Year Final Research Report Summary
Crack-healing behavior of structural ceramics under the conditions of tensile stresses and high temperatures
| Project/Area Number |
15360047
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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 | Yokohama National University |
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Principal Investigator |
ANDO Kotoji Yokohama National University, Energy & Safety Engineering, Professor, 大学院・工学研究院, 教授 (40017992)
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| Co-Investigator(Kenkyū-buntansha) |
TAKAHASHI Koji Yokohama National University, Energy & Safety Engineering, Associate Professor, 大学院・工学研究院, 助教授 (90334630)
NAKAO Wataru Yokohama National University, Energy & Safety Engineering, Research Assistant, 大学院・工学研究院, 助手 (60361870)
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| Project Period (FY) |
2003 – 2004
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| Keywords | Crack-healing / Ceramics / Silicon nitride / Alumina / Mullite / Bending strength / Fatigue strength / Stress intensity factor |
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| Research Abstract |
In this study, Si_3N_4/SiC, alumina/SiC and mullite/SiC composites having excellent crack-healing ability were selected to be test materials. Being introduced a surface-crack of 100 μm, they were then carried out the crack-healing treatment at elevated temperatures raging from 800 to 1200℃ to be applied tensile stress. Based on the strength of the specimens crack-healed under stress, crack-healing behaviors under stress were investigated. From the obtained results, the following conclusions were derived.
1.The heat-treated specimens have same strength as smooth specimens. The cracked specimens could crack-healed under the tensile stress that is 70 to 80% strength of the cracked specimens. The specimens crack-healed under stress had the same strength as the heat-treated smooth specimen at the crack-healed temperature. Moreover, the crack-healed part had enough high strength, because fracture initiation was mostly outside the crack-healed part.
2.The critical condition to be able to heal the pre-crack was estimated from the equation of the stress intensity factor expressed by Newman-Raju and the stress intensity factor of the residual stress for every specimen.
3.The specimens crack-healed under static and cyclic stresses had enough high static and cyclic fatigue strengths at the crack-healing temperature. These values corresponded to 70-80% fracture strength of the crack-healed specimens.
Based on the above conclusions, it is confirmed that Si_3N_4/SiC, alumina/SiC and mullite/SiC composites used in this study can heal cracks initiated in service if the temperature, stress and atmosphere conditions were adjusted.
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