1998 Fiscal Year Final Research Report Summary
A study on the micro-fracture-process and the role of microstructure in the hydrogen induced fracture
| Project/Area Number |
09450052
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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 | KEIO UNIVERSITY |
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Principal Investigator |
YAMADA Kunihiro Keio University, Department of Mechanical Engineering, Professor, 理工学部, 教授 (40051742)
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| Co-Investigator(Kenkyū-buntansha) |
SUZUKI Tetsuya Keio University, Department of Mechanical Engineering, Associate Professor, 理工学部, 助教授 (10286635)
YAMADA Kunihiro Keio University, Department of Mechanical Engineering, Professor (40051742)
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| Project Period (FY) |
1997 – 1998
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| Keywords | Hydrogen Embrittlement / Delayed Fracture / Crack Propagation / Quasi-Cleavge Crack / Intergranular Crack / Microstructure |
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| Research Abstract |
Since most of studies in delayed fracture have dealt with the propagation behavior of macroscopic cracks, no particular attempts to elucidate the behavior of crack initiation and early stage of crack propagation, which is the essential process of hydrogen related fracture, have been made. In this study, to solve the short crack problems of hydrogen induced "brittle fracture" which have been still unsettled, the initiation and propagation behavior of microscopic cracks which start at a weakest site in the microstructure was investigated with a special emphasis on an interaction between mechanical and metallurgical aspects of delayed fracture process.
The experimental analyses have revealed crucial facts which have been remained unknown. The authors had shown in the previous studies that the initial stage of the delayed fracture was not intergranular (IG) but the quasi-cleavage (OC) crack starting from non-metallic inclusions in the subsurface, and that the QC crack triggered IG cracks after a substantial subcritical growth. In this study, it has been revealed that the critical condition for the development of IG cracks is dependent on an increase in the stress intensity at the crack tip (mechanical factor) and the metallurgical changes due to tempering treatment as well as the hydrogen condensation at the crack tip. Consequently, the critical aspects of delayed fracture is related to the material resistance to the transgranular QC crack which should trigger the onset of growth of IG crack, together with the contribution of hydrogen.
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