2019 Fiscal Year Final Research Report
New Crack-Tip Stress Distribution Scaling and its Application to the Prediction of Fracture Toughness Temperature Dependence
| Project/Area Number |
17K06050
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Research Field |
Materials/Mechanics of materials
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| Research Institution | University of Fukui |
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Principal Investigator |
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| Project Period (FY) |
2017-04-01 – 2020-03-31
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| Keywords | 破壊靱性値 / 延性ー脆性遷移温度域 / 温度依存性 / 引張試験 / 降伏応力 / マスターカーヴ |
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| Outline of Final Research Achievements |
Efficient collection of fracture toughness (Jc) is a key in structural integrity evaluation of cracked structures that experience large temperature change. This is because Jc shows approximately 1,400% change with 100℃ change.
This work focused on the fact “fracture stress for slip induced cleavage fracture is temperature independent,” and developed T-scaling method to scale crack-tip stress distribution at fracture between different temperatures.
Finally, T-scaling method was applied to predict Jc temperature dependence as Jc in proportion to (1/σ0) to the (n+1)th power, named as CDS method. Here, n and σ0 is a Ramberg-Osgood exponent and scaling stress, respectively. CDS method was validated for total of 34 cases - combination of material heats and specimen types - including 661 Jc data. Especially, CDS method successfully predicted Jc temperature dependence of Cr-Mo steel (JIS SCM440), which the ASTM E1921 master curve failed to.
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| Free Research Field |
材料力学
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| Academic Significance and Societal Importance of the Research Achievements |
本研究の成果により，き裂部材の材料強さJcの値を広範囲の温度に対し，一温度のJcと降伏応力σ0から予測可能となった．今後インフラの経年劣化が進む中で，試験片に使用できる部材材料が限定される構造物がほとんどであり，本手法は劣化後のその場強度，特に温度依存性の把握を容易に可能とすることが期待される．
学術的意義は，Jcがき裂のない試験片で求められている引張強度（例えば，降伏応力σ0）の一表現である可能性が示唆されたことである．この知見についてはさらなる検討が必要であるが，この場合にはき裂部材，非き裂部材の強度データという仕分けが不要になり，き裂の力学である破壊力学に一石を投じる可能性を秘めている．
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