On the Determination of a Scatter Factor for Fatigue Lives Based on the Lead Crack Concept

Siqueira, Adriano Francisco; Baptista, Carlos Antonio Reis Pereira; Molent, Loris

doi:10.5028/jatm.v5i2.219

ABSTRACT:

The lead crack concept is adopted as the basis for a new fatigue lifeing method using the safe life philosophy. As part of its management strategy, a full-scale fatigue test is conducted to identify high-risk locations in the airframe, and for each item the time for retirement or structural repair is dictated by the safe life limit. A scatter factor is defined to account for the scatter in the material fatigue performance. The fatigue life variation of any given region of aircraft metallic structures is assumed to primarily correlate to the distribution of the equivalent pre-crack size of the fatigue crack initiators. By assuming that the sizes of these crack initiators are independent from each other, the present paper estimates the scatter factor by calculating safe life limit based on known growth characteristics of critical cracks.

KEYWORDS:
Fatigue crack propagation; Aluminum alloys; Scatter factor; Airframe

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REFERENCES

Benoy, M.B., 1981, “Fatigue life variability in civil aircraft”, Proceedings of the 11th ICAF Symposium, Noordwijkerhout, Netherlands.
British Ministry of Defence, 1983, “Design and airworthiness requirements for service aircraft”, v. 1, Aeroplanes of Defence Standard 00-970, Issues 1 to 5.
Cardrick, A.W. and Mew, A.B., 1999, “Scatter considerations in the interpretation of major fatigue tests”, Proceedings ICAF Symposium, Seattle, USA.
Cardrick, A., 2008, “Interpretation of the F/A-18 Bulkhead Tests”, Farnborough.
Forgues, S., 1996, “Study of material and usage variability for probabilistic analyses and scatter factor determination”, RDADSD-123, Bombardier Inc.
Gumbel, E.J., 2004, “Statistic of extremes”, New York, Dover Publications.
Hoffman, M.E. and Hoffman, P.C., 2001, “Corrosion and fatigue research: structural issues and relevance to naval aviation”, International Journal of Fatigue, Vol. 23, S1-S10.
Impellizzeri, L.F., 1966, “Development of a scatter factor applicable to aircraft fatigue life”, Structural Fatigue in Aircraft, ASTM CTP 404, American Society for Testing Materials, p. 136.
Molent, L. and Barter, S.A., 2007, “A comparison of crack growth behavior in several full-scale airframe fatigue tests”, International Journal of Fatigue , Vol. 29, pp. 1090-1099.
Molent, L. and Barter, S.A., 2010, “The lead fatigue crack concept for aircraft structural integrity”, Procedia Engineering, Vol. 2, pp. 363-377.
Molent, L., Barter, S.A. and Wanhill, R.J.H., 2011, “The lead crack fatigue lifeing framework”, International Journal of Fatigue , Vol. 33, pp. 323-331.
Molent, L., Barter, S., White, P. and Dixon, B., 2009a, “Damage tolerance demonstration testing for the Australian F/A-18”, International Journal of Fatigue , Vol. 31, pp. 1031-1038.
Molent, L., Dixon, B., Barter, S., White, P., Mills, T., Maxfield, K., Swanton, G. and Main, B., 2009b, “Enhanced teardown of ex-service F/A-18A/B/C/D centre fuselages”, Proceedings ICAF, Rotterdam.
Molent, L., Sun, Q. and Green, A.J., 2006, “Characterization of equivalent initial flaw sizes in 7050 aluminum alloy”, Fatigue & Fracture of Engineering Materials & Structures, Vol. 29, pp. 916-937.
Parish, H.E., 1965, “Fatigue test results and analysis of 42 provost wings”, Reports and Memoranda No. 3474, Aeronautical Research Council.
Pell, R.A., Molent, L. and Green, A.J., 2004, “The fractographical comparison of F/A-18 aluminum alloy 7050-T7451 bulkhead representative coupons tested under two fatigue load spectra at several test levels”, DSTO-TR-1547, Melbourne, Australia.
Stagg, A.M., 1969, “Scatter in fatigue: elements and sections from aircraft structures”, CP No. 1357, Her Majesty’s Stationary Office.
Underhill, P.R. and DuQuesnay, D.L., 2008, “The effect of dynamic loading on the fatigue scatter factor for Al 7050”, International Journal of Fatigue , Vol. 30, pp. 614-622.
United States Air Force - USAF, 1974, “Military specification airplane damage tolerance requirements”, MIL-A-83444, United States Military Standard.
White, P., Molent, L. and Barter, S., 2005, “Interpreting fatigue test results using a probabilistic fracture approach”, International Journal of Fatigue , Vol. 27/7, pp. 752-767.
Young, L. and Ekvall, J.C., 1981, “Reliability of fatigue testing”, Statistical Analysis of Fatigue Data, ASTM STP 744, American Society for Testing and Materials, pp. 55-74.

Publication Dates

Publication in this collection
Apr-Jun 2013

History

Received
17 Dec 2012
Accepted
18 Apr 2013

This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

[1] Benoy, M.B., 1981, “Fatigue life variability in civil aircraft”, Proceedings of the 11th ICAF Symposium, Noordwijkerhout, Netherlands.

[2] British Ministry of Defence, 1983, “Design and airworthiness requirements for service aircraft”, v. 1, Aeroplanes of Defence Standard 00-970, Issues 1 to 5.

[3] Cardrick, A.W. and Mew, A.B., 1999, “Scatter considerations in the interpretation of major fatigue tests”, Proceedings ICAF Symposium, Seattle, USA.

[4] Cardrick, A., 2008, “Interpretation of the F/A-18 Bulkhead Tests”, Farnborough.

[5] Forgues, S., 1996, “Study of material and usage variability for probabilistic analyses and scatter factor determination”, RDADSD-123, Bombardier Inc.

[6] Gumbel, E.J., 2004, “Statistic of extremes”, New York, Dover Publications.

[7] Hoffman, M.E. and Hoffman, P.C., 2001, “Corrosion and fatigue research: structural issues and relevance to naval aviation”, International Journal of Fatigue, Vol. 23, S1-S10.

[8] Impellizzeri, L.F., 1966, “Development of a scatter factor applicable to aircraft fatigue life”, Structural Fatigue in Aircraft, ASTM CTP 404, American Society for Testing Materials, p. 136.

[9] Molent, L. and Barter, S.A., 2007, “A comparison of crack growth behavior in several full-scale airframe fatigue tests”, International Journal of Fatigue , Vol. 29, pp. 1090-1099.

[10] Molent, L. and Barter, S.A., 2010, “The lead fatigue crack concept for aircraft structural integrity”, Procedia Engineering, Vol. 2, pp. 363-377.

[11] Molent, L., Barter, S.A. and Wanhill, R.J.H., 2011, “The lead crack fatigue lifeing framework”, International Journal of Fatigue , Vol. 33, pp. 323-331.

[12] Molent, L., Barter, S., White, P. and Dixon, B., 2009a, “Damage tolerance demonstration testing for the Australian F/A-18”, International Journal of Fatigue , Vol. 31, pp. 1031-1038.

[13] Molent, L., Dixon, B., Barter, S., White, P., Mills, T., Maxfield, K., Swanton, G. and Main, B., 2009b, “Enhanced teardown of ex-service F/A-18A/B/C/D centre fuselages”, Proceedings ICAF, Rotterdam.

[14] Molent, L., Sun, Q. and Green, A.J., 2006, “Characterization of equivalent initial flaw sizes in 7050 aluminum alloy”, Fatigue & Fracture of Engineering Materials & Structures, Vol. 29, pp. 916-937.

[15] Parish, H.E., 1965, “Fatigue test results and analysis of 42 provost wings”, Reports and Memoranda No. 3474, Aeronautical Research Council.

[16] Pell, R.A., Molent, L. and Green, A.J., 2004, “The fractographical comparison of F/A-18 aluminum alloy 7050-T7451 bulkhead representative coupons tested under two fatigue load spectra at several test levels”, DSTO-TR-1547, Melbourne, Australia.

[17] Stagg, A.M., 1969, “Scatter in fatigue: elements and sections from aircraft structures”, CP No. 1357, Her Majesty’s Stationary Office.

[18] Underhill, P.R. and DuQuesnay, D.L., 2008, “The effect of dynamic loading on the fatigue scatter factor for Al 7050”, International Journal of Fatigue , Vol. 30, pp. 614-622.

[19] United States Air Force - USAF, 1974, “Military specification airplane damage tolerance requirements”, MIL-A-83444, United States Military Standard.

[20] White, P., Molent, L. and Barter, S., 2005, “Interpreting fatigue test results using a probabilistic fracture approach”, International Journal of Fatigue , Vol. 27/7, pp. 752-767.

[21] Young, L. and Ekvall, J.C., 1981, “Reliability of fatigue testing”, Statistical Analysis of Fatigue Data, ASTM STP 744, American Society for Testing and Materials, pp. 55-74.

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