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Research Papers: Materials and Fabrication

Multiple Fatigue Crack Growth Prediction Using Stress Intensity Factor Solutions Modified by Empirical Interaction Factors

[+] Author and Article Information
Shinji Konosu

 Ibaraki University 4-12-1, Nakanarusawa, Hitachi, Ibaraki 316-8511, Japankonosu@mx.ibaraki.ac.jp

Kyosuke Kasahara1

Graduate School of Ibaraki Universityky-kasahara@jfe-steel.co.jp

1

Present address: JFE Steel Corporation, 1, Kokancyo Fukuyama, Hiroshima 721-8510, Japan.

J. Pressure Vessel Technol 134(1), 011404 (Dec 20, 2011) (12 pages) doi:10.1115/1.4004570 History: Received June 08, 2010; Revised June 27, 2011; Published December 20, 2011; Online December 20, 2011

It is generally believed that multiple fatigue crack growth prediction is difficult with the use of conventional stress intensity factor (SIF) solution calculations because of issues such as SIF magnification and shielding effects. Therefore, almost all the existing Fitness for Service (FFS) rules such as the ASME Code Section XI and JSME Code adopt the procedure whereby multiple cracks grow independently after applying a certain alignment rule based on the initial crack configuration and are combined immediately into an enveloping crack when the crack tips touch. In some cases, the results of the procedures in the existing FFS rules are less accurate in predictions of the service life of cracked components. Therefore, there is still room for improvement, although the procedures are simple for utilities. This paper describes a new approach to predict fatigue crack growth life of multiple nonaligned cracks by the use of SIF solutions modified by empirical interaction factors. Several examples of two nonaligned cracks illustrate the accuracy and effectiveness of the procedure by comparison with numerical analysis by the body force method for two-dimensional problems and with the experimental results given in the literature for three-dimensional problems.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Configuration of multiple nonaligned cracks

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Figure 2

Angle of crack extension θm at tip A for two parallel cracks

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Figure 3

Interaction-affected area whereby multiple fatigue cracks should be treated dependently

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Figure 4

Crack tip overlap distances Xcom, in which nonaligned cracks are assumed to be combined into an enveloping crack

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Figure 5

Flowchart of fatigue life prediction for multiple nonaligned cracks

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Figure 6

(a) Comparison of simulation result between proposed procedure and body force method for Case 2D.1a where initial crack lengths are 5 mm (Cf=3.779×10-12S,S=25.72(2.88-R)-3.07,m=3.07). (b) Comparison of simulation result between proposed procedure and body force method for Case 2D.1b, where initial crack lengths are 30 mm (Cf=3.779×10-12S,S=25.72(2.88-R)-3.07,m=3.07).

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Figure 7

Comparison of simulation result between proposed procedure and body force method for Case 2D.2 (Cf=3.779×10-12S,S=25.72(2.88-R)-3.07,m=3.07)

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Figure 8

Comparison of simulation result between proposed procedure and body force method for Case 2D.3 (Cf=3.78×10-12S,S=25.72(2.88-R)-3.07,m=3.07)

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Figure 9

Experimental (Leek and Howard [1]: A508 Class3) and predicted crack growth for Case 3D.1 by using actually measured material constants Cf=3.318×10-12,m=3.056.

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Figure 10

Experimental (Leek and Howard [1]: A508 Class3) and predicted crack growth for Case 3D.2 by using actually measured material constants Cf=3.318×10-12,m=3.056.

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Figure 11

Experimental (Ando [2]: A533 Gr.B Class1) and predicted crack growth for Case 3D.3 by using actually measured material constants Cf=1.67×10-12,m=3.23.

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