Fatigue cracks are prone to develop around the fasteners found in multilayer aluminum structures such as aging aircraft. The
determination of their probability of detection (POD) using eddy current techniques is critical for risk assessments used in
evaluating serviceability. Normally, a large number of samples of both fatigue cracks and electric discharge machined notches
are required for such a study. In this study, the use of quantitative fractography (QF) to efficiently gather probability of detection
(POD) data for bolt hole eddy current is demonstrated. The technique can be readily automated, significantly reducing
man-hour requirements. The method is applied to mid-bore cracks, grown without starter notches, in order to simulate naturally
occurring fatigue cracks. POD of the mid-bore cracks is examined using a probit analysis. An a90/95, the probability that
90% of the cracks of size a or larger will be detected 95% of the time, of 0.34 mm was obtained for mid-bore crack depth.
This value is consistent with skin depth considerations at the 1.6 MHz inspection frequency. An examination of the POD
based on crack length found that it was related to that of depth according to the average length-to-depth aspect ratio of 2 to 1.
1. Berens, A. “NDE Reliability Data Analysis,” Nondestructive Evaluation and Quality Control, ASM International Metals
Handbook, Ninth Edition, Volume 17, pp. 689-701.
2. Khan, M., M. Yanishevsky and A. Fahr. “Bolt Hole Eddy Current Testing Probability of Detection, Part - I: Experimental
Design and Data Analysis,” 12th International Conference on Fracture, Ottawa, July 13-17, 2009.
3. Lemire, H., P.R. Underhill, T.W. Krause, M. Bunn and D.J. Butcher. “Improving Probability of Detection of Bolt Hole
Eddy Current Inspection,” Research in Nondestructive Evaluation, 21, No. 3, pp. 141-156, 2010.
4. Molent, L., Q. Sun and J. Green. “Characterization of equivalent flaw sizes in 7050 aluminum alloy,” Fatigue fract.
Engng. Mater. Struct., 29, pp. 916-937, 2006.
5. Molent, L., R. Singh and J. Woolsey. “A method of evaluation of in-service fatigue cracks,” Engineering Failure Analysis,
12, pp. 13-24, 2005.
6. Molent, L., R. Jones, S. Barter and S. Pitt. “Recent developments in fatigue crack assessment,” Int. J. Fatigue, 28, pp.
1759-1768, 2006.
7. Schijve, J. “The significance of fractography for investigations to fatigue crack growth under variable amplitude loading,”
Fatigue Fract. Engng. Mater. Struct., 22, pp. 87-99, 1999.
8. Underhill, P.R. and D. DuQuesnay. “Effect of small cycles and load spectrum truncation on the fatigue life scatter in
7050 Al alloy,” J. Fatigue, 31, pp. 538-543, 2009.
9. Underhill, P.R. and T.W. Krause. “Investigation of Parameters Affecting Crack Detection in Bolt Hole Eddy Current,”
3rd International CANDU In-Service Inspection and NDT In Canada 2010 Conference, Markham, Ontario, June 14-17,
2010.
10. Pampel, F.C. Logistic Regression: A Primer, Sage Publications, Thousand Oaks, CA, 2000.
11. Cecco, V.S., G. Van Drunen and F.L. Sharp. Eddy Current Manual, Volume 1: Test Method, Chalk River Nuclear Laboratories,
AECL-7523, Nov. 1981, pp.11, 13, 14, 48 and 66.
12. Lemire, H., T.W. Krause, M. Bunn and D.J. Butcher, “Variables Affecting Probability of Detection in Bolt Hole Eddy
Current Inspection,” Review of Progress in Quantitative Nondestructive Evaluation, Volume 28B, pp. 1808-1815, edited
by: D.O. Thompson and D.E. Chimenti, ISBN 978-0-7354-0629-2, Melville, NY (© 2009 American Institute of Physics).