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Research Papers: Materials and Fabrication

Evaluation of Fracture Toughness by Master Curve Approach Using Miniature C(T) Specimens

[+] Author and Article Information
Naoki Miura

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

Naoki Soneda

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

J. Pressure Vessel Technol 134(2), 021402 (Jan 11, 2012) (9 pages) doi:10.1115/1.4005390 History: Received September 12, 2010; Revised October 14, 2011; Accepted October 16, 2011; Published January 11, 2012; Online January 11, 2012

The fracture toughness master curve shows the relationship between the median of fracture toughness and temperature in the ductile–brittle transition temperature region of ferritic steels such as reactor pressure vessel (RPV) steels. The master curve approach specified in the ASTM standard theoretically provides the confidence levels of fracture toughness in consideration with the inherent scatter of fracture toughness. The authors have conducted several fracture toughness tests for typical Japanese RPV steels with various specimen sizes and shapes and ascertained that the master curve can be accurately applied to the specimens with a thickness of 0.4-in. or larger. With respect to using the master curve method with the current surveillance program for operating RPVs, the utilization of miniature specimens is important. Miniature specimens, which can be taken from the broken halves of surveillance specimens, are necessary for the efficient determination of the master curve from the limited volume of the available materials. In this study, fracture toughness tests were conducted for typical Japanese RPV steels, particularly SFVQ1A forged and SQV2A plate materials, using the miniature C(T) specimens with a thickness of 4 mm, following the procedure in the ASTM standard. The results show that the differences in the test temperature, evaluation method, and specimen size did not affect the master curves, and the fracture toughness indexed by the reference temperature, To , obtained from miniature C(T) specimens were consistent with those obtained from the standard and larger C(T) specimens. It was also found that valid reference temperatures can be determined with a realistic number of miniature C(T) specimens, i.e., less than ten, if the test temperature was appropriately selected. Thus, the master curve method using miniature C(T) specimens could be a practical method to determine the fracture toughness of actual RPV steels.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Dependence of Young’s modulus on temperature

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Figure 2

Dependence of yield stress on temperature

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Figure 3

Orientation of a miniature specimen, taken from the broken half of a Charpy specimen: (a) miniature C(T) specimen (b) subsize PCCv specimen

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Figure 4

Shape and size of miniature specimens: (a) miniature C(T) specimen (b) subsize PCCv specimen

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Figure 5

Miniature C(T) specimen instrumented with a clip gauge and fixtures

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Figure 6

Relationships between equivalent fracture toughness and test temperature: (a) miniature C(T), SFVQ1A forging; (b) miniature C(T), SQV2A (Heat 1) plate; (c) miniature C(T), SQV2A (Heat 2) plate; and (d) subsize PCCv, SFVQ1A forging

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Figure 7

Effect of test temperature and evaluation method on reference temperature

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Figure 8

Comparison of master curves and fracture toughness data: (a) miniature C(T), SFVQ1A forging; (b) miniature C(T), SQV2A (Heat 1) plate; (c) miniature C(T), SQV2A (Heat 2) plate; and (d) subsize PCCv, SFVQ1A forging

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Figure 9

Dimensions of miniature C(T) specimen

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Figure 10

Relationship between a/W and V/V′

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Figure 11

Schematic of specimen deformation

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Figure 12

Relationship between V and V′ for finite deformation

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Figure 13

Effect of specimen type and size on reference temperature: (a) SFVQ1A forging; (b) SQV2A (Heat 1) plate; and (c) SQV2A (Heat 2) plate

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Figure 14

Relationship between ratio of valid data and T–To

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Figure 15

Relationship between possible number of data for valid evaluation and T–To

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Figure 16

Comparison of miniature C(T) test data, master curve tolerance bounds, and KIc (a) SFVQ1A forging (b) SQV2A (Heat 1) plate; and (c) SQV2A (Heat 2) plate

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