2002 Fiscal Year Final Research Report Summary
Study on Statistical Giga-cycle Fatigue Property of High Strength Steels and Establishment of Reliability Assurance Engineering
| Project/Area Number |
11650106
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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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 | Ritsumeikan University |
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Principal Investigator |
SAKAI Tatsuo Ritsumeikan Univ., Fac. Science and Engineering, Professor, 理工学部, 教授 (00066739)
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| Project Period (FY) |
1999 – 2002
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| Keywords | High strength steels / Reliability analysis / Statistical fatigue property / Ultra-long life fatigue / Mixed Weibull distribution / Duplex S-N property / Fatigue strength / Fish-eye |
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| Research Abstract |
Main results in this research are summarized as follows;
(1) Two-step S-N curve often reported on several high strength steels and case-hardened steels can be well interpreted as the duplex S-N curves consisting of two different S-N curves for the respective fracture modes of surface induced fracture and interior inclusion induced fracture.
(2) Above duplex S-N characteristics in the long life regime are common for the rotating bending and the axial loading but the separation of the respective S-N curves in the rotating bending is distinct more than that in the axial loading.
(3) Slope of the S-N curve in the interior inclusion induced fracture is less than that in the surface induced fracture. This aspect can be attributed to the difference of the fatigue crack growth laws in the room air and in the vacuum.
(4) Stress intensity factor range at the front of the fine granular area (FGA) around the interior inclusion at the crack origin is corresponding to the threshold value of the fatigue crack propagation of the material ΔK_<th>.
(5) Fatigue life distribution at a stress level is well explained as the mixed mode of Weibull distribution consisting of the respective life components of the surface induced fracture and the interior inclusion induced fracture. Statistical fatigue properties can be quantitatively analyzed through the stress dependence of Weibull parameters for the respective fatigue life distribution.
(6) Total fatigue life of the bearing steel can be separated into three components for the crack initiation life, the formation life of FGA and the formation life of the fish-eye.
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