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Research Papers: Design and Analysis

Technical Basis for Application of Weight Function Method for Calculation of Stress Intensity Factor for Surface Flaws Proposed for ASME Section XI Appendix A

[+] Author and Article Information
Douglas A. Scarth

Kinectrics, Inc.,
800 Kipling Avenue,
Toronto, ON, M8Z 5G5, Canada

Russell C. Cipolla

Intertek APTECH,
601 West California Avenue,
Sunnyvale, CA 94086

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received January 8, 2012; final manuscript received January 26, 2013; published online September 18, 2013. Assoc. Editor: Somnath Chattopadhyay.

J. Pressure Vessel Technol 135(5), 051209 (Sep 18, 2013) (9 pages) Paper No: PVT-12-1004; doi: 10.1115/1.4024439 History: Received January 08, 2012; Revised January 26, 2013

Analytical evaluation procedures for determining the acceptability of flaws detected during in-service inspection of nuclear power plant components are provided in Section XI of the ASME Boiler and Pressure Vessel Code. Linear elastic fracture mechanics based evaluation procedures in ASME Section XI require calculation of the stress intensity factor. A method for calculating the stress intensity factor is provided in Appendix A of ASME Section XI. This method consists of a two-step process. In the first step, the stress distribution, as calculated in the absence of the flaw, is obtained at the flaw location. For a surface flaw, the stress distribution at the flaw location is then fitted to a third-order polynomial equation. In the second step, the fitted polynomial representation of the stress distribution is used with standardized influence coefficients to calculate the stress intensity factor. An alternate method for calculation of the stress intensity factor for a surface flaw that makes explicit use of the universal weight function method and does not require a polynomial fit to the actual stress distribution is proposed in this paper for implementation into Appendix A of ASME Section XI. Universal weight function coefficients are determined from standardized influence coefficients through closed-form equations. Closed-form equations for calculation of the stress intensity factor are provided. The technical basis and verification for this alternate method for calculation of the stress intensity factor are described in this paper.

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Figures

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Fig. 1

Axial part-through-wall planar surface flaw in a cylinder

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Fig. 2

Circumferential part-through-wall planar surface flaw in a cylinder

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Fig. 3

Stress distribution acting over the crack depth

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Fig. 4

Piece-wise linear representation of stress over discrete intervals with specified stress data at discrete locations

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Fig. 5

Discrete data points of applied stress σ0(x/a) 3.5 on the crack faces and cubic polynomial fits of stress distribution

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Fig. 6

Results of nondimensional stress intensity factor KI/(σ0√πa/Q) for an internal axial surface crack in a cylinder with Ri/t = 2 and a/c = 0.4 based on universal weight function method

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Fig. 7

Results of nondimensional stress intensity factor KI/(σ0√πa/Q) for an internal axial surface crack in a cylinder with Ri/t = 2 and a/c = 0.4 based on cubic polynomial stress equations

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