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Research Papers: Materials and Fabrication

Inherent-Strain-Based Theory of Measurement of Three-Dimensional Residual Stress Distribution and Its Application to a Welded Joint in a Reactor Vessel

[+] Author and Article Information
Keiji Nakacho

Joining and Welding Research Institute,
Osaka University,
Mihogaoka 11-1, Ibaraki City,
Osaka 567-0047, Japan
e-mail: nakacho@jwri.osaka-u.ac.jp

Naoki Ogawa

Takasago Research & Development Center,
Technology & Innovation Headquarters,
Mitsubishi Heavy Industries, Ltd.,
1-1 Shinhama, 2-chome, Arai-cho,
Takasago City,
Hyogo 676-8686, Japan
e-mail: naoki2_ogawa@mhi.co.jp

Takahiro Ohta

Nagasaki Research & Development Center,
Technology & Innovation Headquarters,
Mitsubishi Heavy Industries, Ltd.,
717-1, Fukahori-machi, 5-chome,
Nagasaki City,
Nagasaki 851-0392, Japan
e-mail: takahiro_ohta@mhi.co.jp

Michisuke Nayama

Technology & Innovation Headquarters,
Mitsubishi Heavy Industries, Ltd.,
16-5 Konan 2-chome,
Minato-ku,
Tokyo 108-8215, Japan
e-mail: michisuke_nayama@mhi.co.jp

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received June 10, 2013; final manuscript received January 9, 2014; published online February 27, 2014. Assoc. Editor: Xian-Kui Zhu.

J. Pressure Vessel Technol 136(3), 031401 (Feb 27, 2014) (11 pages) Paper No: PVT-13-1099; doi: 10.1115/1.4026496 History: Received June 10, 2013; Revised January 09, 2014

The stress that exists in a body under no external force is called the inherent stress. The strain that is the cause (source) of this stress is called the inherent strain. This study proposes a general theory of an inherent-strain-based measurement method for the residual stress distributions in arbitrary three-dimensional bodies and applies the method to measure the welding residual stress distribution of a welded joint in a reactor vessel. The inherent-strain-based method is based on the inherent strain and the finite element method. It uses part of the released strains and solves an inverse problem by a least squares method. Thus, the method gives the most probable value and deviation of the residual stress. First, the basic theory is explained in detail, and then a concrete measurement method for a welded joint in a reactor vessel is developed. In the method, the inherent strains are unknowns. In this study, the inherent strain distribution was expressed with an appropriate function, significantly decreasing the number of unknowns. Five types of inherent strain distribution functions were applied to estimate the residual stress distribution of the joint. The applicability of each function was evaluated. The accuracy and reliability of the analyzed results were assessed in terms of the residuals, the unbiased estimate of the error variance, and the welding mechanics. The most suitable function, which yields the most reliable result, was identified. The most reliable residual stress distributions of the joint are shown, indicating the characteristics of distributions with especially large tensile stress that may produce a crack.

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References

Figures

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Fig. 4

Mesh division of mock-up (a) entire mock-up, and (b) around the welded zone

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Fig. 5

Inherent strain region

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Fig. 6

Unbiased estimate of error variance

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Fig. 7

Residual stress σz at 0deg-180deg section (a) most probable value, and (b) standard deviation

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Fig. 8

Residual stress σr at 0deg-180deg section (a) most probable value, and (b) standard deviation

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Fig. 9

Residual stress σθ at 0deg-180deg section (a) most probable value, and (b) standard deviation

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Fig. 10

Residual stress σz on upper surface (a) most probable value, and (b) standard deviation

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Fig. 11

Residual stress σr on upper surface (a) most probable value, and (b) standard deviation

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Fig. 12

Residual stress σθ on upper surface (a) most probable value, and (b) standard deviation

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Fig. 1

Mock-up of welded joint in reactor vessel

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Fig. 2

Procedure for measuring and cutting

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Fig. 3

Measurement locations (a) T specimens (0deg, 180deg), and (b) L specimens (0deg-180deg)

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