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Research Papers: Design and Analysis

A Criterion for Combination Rule in Flaw Assessment of Parallel Surface Cracks

[+] Author and Article Information
Masayuki Kamaya

 Institute of Nuclear Safety System, Inc., 64 Sata, Mihama-cho, Fukui 919-1205, Japankamaya@inss.co.jp

J. Pressure Vessel Technol 133(6), 061204 (Oct 19, 2011) (8 pages) doi:10.1115/1.4004563 History: Received March 10, 2010; Accepted June 06, 2011; Published October 19, 2011; Online October 19, 2011

When multiple cracks approach one another, the stress intensity factor and J-integral value change due to the interaction of the stress field. Since the changes in these parameters are not always conservative in structural reliability evaluations, the interaction between multiple cracks should be taken into account. Section XI of the ASME Boiler and Pressure Vessel Code provides a flaw characterization rule for interacting multiple cracks. In Section XI, adjacent cracks are replaced with a coalesced single crack when the distance between the cracks is less than half of the crack depth. However, the criterion for the offset distance is given as an absolute value, although the magnitude of the interaction depends on the crack size. In the current study, an alternative criterion for the offset distance was examined. Linear-elastic and elastic–plastic analyses were performed for interacting semicircular and semi-elliptical surface cracks by the finite element method under a tensile or bending load. The change in the stress intensity factors and J-integral values due to the relative spacing of cracks was investigated. Based on the relationship between the magnitude of the interaction and the relative position of the cracks, the allowable ctriterion for the offset distance was discussed.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Crack coalescence criteria for noncoplanar cracks (ASME Sec. XI [11] and JSME Code [12])

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Figure 7

Normalized SIF for multiple surface cracks (S/c = −0.4, H/c = 0.4)

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Figure 17

Relationship between distance S and SIF at inner crack tip under different thickness (H = 0, a/c = 1.0)

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Figure 16

Change in the maximum SIF for offset distance H under different thicknesses (a/c = 1.0, arrows indicate K/Ko for (S/a, H/a) = (0.5, 0.0) for each thickness condition)

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Figure 15

Relationship between distance S and the maximum J-value (H = 0)

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Figure 14

Relationship between distance S and SIF at inner crack tip (H = 0)

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Figure 13

Change in the maximum J-value for offset distance H

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Figure 12

Change in normalized J-value of coplanar cracks with applied stress under various combinations of material properties (bending)

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Figure 11

Change in normalized J-value of coplanar cracks with applied stress under various combinations of material properties (tension)

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Figure 10

J-value of coplanar cracks along crack front under different applied tensile loads (S = 0.4a, α = 1.5, n = 10)

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Figure 9

Change in the maximum SIF for offset distance H

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Figure 8

Relationship between SIF and relative position of semicircular surface cracks

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Figure 6

Normalized SIF of semicircular surface crack

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Figure 5

An example of finite element mesh for parallel surface cracks (Position of cracks: S/a = −0.5, H/a = 0.5)

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Figure 4

Finite element mesh around the crack front

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Figure 3

Schematic drawing representing the crack blocks and tie block

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Figure 2

Schematic drawing showing definitions of the geometry for a plate with two surface cracks

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