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Research Papers: Design and Analysis

Rational Determination of Lower-Bound Fracture Toughness Curves Using Master Curve Approach

[+] Author and Article Information
Naoki Miura

e-mail: miura@criepi.denken.or.jp

Naoki Soneda

e-mail: soneda@criepi.denken.or.jp
Materials Science Research Laboratory,
Central Research Institute of Electric
Power Industry,
2-6-1 Nagasaka, Yokosuka-shi,
Kanagawa 240-0196, Japan

Shu Sawai

e-mail: shu.sawai@gmail.com

Shinsuke Sakai

e-mail: sakai@fml.t.u-tokyo.ac.jp
The University of Tokyo,
7-3-1, Hongo, Bunkyo-ku,
Tokyo 113-8656, Japan

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received January 23, 2013; final manuscript received June 25, 2013; published online October 10, 2013. Assoc. Editor: David L. Rudland.

J. Pressure Vessel Technol 135(6), 061211 (Oct 10, 2013) (7 pages) Paper No: PVT-13-1020; doi: 10.1115/1.4025088 History: Received January 23, 2013; Revised June 25, 2013

The Master Curve gives the relation between the median of fracture toughness of ferritic steels and the temperature in the ductile–brittle transition temperature region. The procedure used to determine the Master Curve is provided in the current American Society for Testing and Materials (ASTM) E1921 standard. By considering the substitution of the alternative lower-bound curves based on the Master Curve approach for the KIc curves based on reference data sets in the present codes such as ASME Code Cases N-629 and N-631, the statistical characteristic should be well incorporated in the determination of the lower-bound curves. Appendix X4 in the ASTM standard describes the procedure used to derive the lower-bound curves; however, it appears to be addressed without sufficient consideration of the statistical reliability. In this study, we propose a rational determination method of lower-bound fracture toughness curves using the Master Curve approach. The method considers the effect of sample size in the determination of the tolerance-bound curve. The adequacy of the proposed method was verified by comparing the tolerance-bound curve with the fracture toughness database for national reactor pressure vessel (RPV) steels including plate and forging obtained from 4 T to 0.4 T C(T) specimens and 0.4 T SE(B) specimens. The method allows the application of the Master Curve using fewer specimens, which can coexist with the present surveillance program.

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References

Figures

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Fig. 3

Evaluation results of reference temperature To: (a) SFVQ1A, (b) SQV2A heat 1, and (c) SQV2A heat 2

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Fig. 5

Apparent standard deviation of KJc, uKJc: (a) SFVQ1A, (b) SQV2A heat 1, and (c) SQV2A heat 2

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Fig. 2

Dependence of yield stress on temperature

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Fig. 1

Dependence of Young's modulus on temperature

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Fig. 4

Effect of T − To on reference temperature To: (a) SFVQ1A, (b) SQV2A heat 1, and (c) SQV2A heat 2

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Fig. 9

Effect of sample size N on tolerance-bound reducing factor κ

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Fig. 6

Apparent standard deviation of To, uTo: (a) SFVQ1A, (b) SQV2A heat 1, and (c) SQV2A heat 2

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Fig. 7

Effect of sample size N on estimator of standard deviation of KJc(med) [8]

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Fig. 8

Schematic expression of tolerance-bound reducing factor κ

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Fig. 10

Comparison of tolerance bounds

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Fig. 11

Comparison of experimental fracture toughness data and lower-bound curves: (a) SFVQ1A, (b) SQV2A heat 1, and (c) SQV2A heat 2

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