2006 Fiscal Year Final Research Report Summary
Elucidation of effect of hydrogen on giga-cycle fatigue mechanism and establishment of improvement method of fatigue strength reliability
| Project/Area Number |
14001002
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| Research Category |
Grant-in-Aid for Specially Promoted Research
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| Allocation Type | Single-year Grants |
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| Review Section |
Physics
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| Research Institution | Kyushu University |
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Principal Investigator |
YUKITAKA Murakami Kyushu University, Faculty of Engineering, Professor, 大学院・工学研究院, 教授 (10038010)
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| Co-Investigator(Kenkyū-buntansha) |
KONDO Yoshiyuki Kyushu University, Faculty of Engineering, Professor, 大学院・工学研究院, 教授 (90325499)
NOGUCHI Hiroshi Kyushu University, Faculty of Engineering, Professor, 大学院・工学研究院, 教授 (80164680)
MATSUOKA Saburo Kyushu University, Faculty of Engineering, Associate Professor, 大学院・工学研究院, 助教授 (10354250)
TAKAI Kenichi Sophia University, Faculty of Science and Engineering, Associate Professor, 理工学部, 助教授 (50317509)
MATSUNAGA Hisao Fukuoka University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (80346816)
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| Project Period (FY) |
2002 – 2006
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| Keywords | Giga-cycle fatigue / Hydrogen / Optically Dark Area / The area parameter model / Nonmetallic inclusion / Slip / Tritium autoradiography / Fuel cell system |
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| Research Abstract |
In recent years, a special concern has been raised about the development and commercialization of fuel cell (FC) systems to solve both the global warming and energy problems. Under such circumstance, the role of this research project has been significantly increasing to ensure the safety use of FC systems in the near future. In this project, the effect of hydrogen on giga-cycle fatigue mechanism in high strength steels has been studied as well as the effect of hydrogen on fatigue properties of candidate materials for FC systems. The obtained results are as follows:
(1) The evidences of interaction of hydrogen on giga-cycle fatigue failure have been shown by the fatigue tests of hydrogen-content-controlled specimens, the secondary ion mass spectrometry and the tritium autoradiography.
(2) The giga-cycle fatigue mechanism taking the hydrogen interaction into consideration has been proposed. It has been shown that the giga-cycle fatigue strength can be improved by controlling hydrogen content in materials, inclusion size and inclusion type.
(3) A fatigue design method in giga-cycle regime has been proposed based on the area parameter model, the statistics of extremes and the growth curve of the optically dark area (ODA).
(4) A number of reliable fatigue data on the effect of hydrogen has been obtained about the candidate materials for FC systems. In addition, some important findings about the degradation mechanism due to hydrogen have been given, e.g. the slip localization due to hydrogen and the effect of phase transformations on the crack-growth acceleration, etc.
Considering all the results in this project, the following two significant conclusions have been obtained:
(I) Hydrogen does not cause so-called "embrittlement" of materials, but facilitates the dislocation mobility resulting in the slip concentration.
(II) The role of hydrogen trapped by inclusions in giga-cycle fatigue mechanism is to cause the microscopic slip concentration even at the lower stress.
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