A Modified Compliance Method for Automatically Measuring Fatigue Crack Growth In Situ during Spectrum Fatigue Testing

Abstract:

The fatigue critical structures of military aircraft are generally subjected to variable amplitude flight spectrum loading. Maintaining aircraft structural integrity to ensure safe operation of the fleet is critically dependent on accurate analysis and reliable prediction of fatigue crack growth in those structures under service operating conditions. To achieve this goal, laboratory experimental methods that can accurately measure and monitor fatigue crack growth under variable amplitude loading are required. This can be challenging as no test standard exists to guide the process of fatigue crack growth measurement under variable amplitude loading conditions to ensure the accuracy of the test results. This challenge was addressed by developing a modified compliance method as described in this paper. The results presented employed a modified compliance method complemented with a travelling microscope technique and marker band loads. The modified compliance method developed is able to measure in-situ, fatigue crack growth of standard compact-tension specimens under a fighter flight spectrum loading. The marker band loads and microscope readings were used to assist the post-test validation using quantitative fractography. The results from this study have demonstrated that the modified compliance method can produce consistent and accurate fatigue crack growth data under variable amplitude loading conditions.

• Periodical: Advanced Materials Research (Volumes 891-892)
• Pages: 732-738
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.891-892.732
• Online since: March 2014
• Authors: Wyman Zhuang*, Qian Chu Liu
• Keywords: Aluminium Alloy, Experimental Technique, Fatigue Crack Growth (FCG), Modified Compliance, Quantitative Fractography, Spectrum Loading

References

[1] J. Schijve, Fatigue damage in aircraft structures, not wanted, but tolerated? International Journal of Fatigue, 31(2009) 998-1011.

DOI: 10.1016/j.ijfatigue.2008.05.016

[2] W. Zhuang, M. McDonald, M. Phillips and L. Molent, Effective block approach for aircraft damage tolerance analyses, AIAA Journal of Aircraft, 46 (2009) 1660-1666.

DOI: 10.2514/1.42306

[3] ASTM Standard Test Method for Measurement of Fatigue Crack Growth Rates, ASTM E64711, The American Society for Testing and Materials, (2011).

[4] J.K. Donald and K. George, Variable amplitude fatigue crack growth using digital signal processing technology, ASTM STP 1439, American Society for Testing and Materials, (2002).

DOI: 10.1520/stp11297s

[5] J.K. Donald, Automated fatigue crack growth testing and analysis - Series 2001 Version 3. 12, Fracture Technology Associates, July (2013).

[6] H. Proudhon, A. Moffat, J-Y. Buffière and I. Sinclair, In situ three dimensional monitoring and modelling of small corner cracks in airframe Al alloys, Proceedings of International Conference on Fracture (ICF12), Ottawa, Canada, (2009).

[7] P. McKeigham, C. Tabrett and D. Smith, The influence of crack deflection and bifurcation on DC Potential Drop Calibration, ASTM STP 1251, American Society for Testing and Materials, (1995) 51-66.

DOI: 10.1520/stp14677s

[8] D. Mongru, P. Jacjson, K. Maxfield and C. Wallbrink, Evaluation of alternative life assessment approaches using P-3 SLAP test results, DSTO-TR-2418, DSTO Melbourne, (2010).

[9] P.K. Sharp, D.E. Rowlands and G. Clark, Evaluation of innovative NDI methods for detection of service simulation cracking, DSTO-TR-0366, DSTO Melbourne, (1996).

[10] M. Giglio and A. Manes, Effect of flight spectrum loads on the damage tolerance evaluation of a helicopter frame, A. Öchsner et al. (eds. ), Materials with Complex Behaviour, Advanced Structured Materials 6, Springer-Verlag Berlin Heidelberg, (2010).

DOI: 10.1007/978-3-642-12667-3_20

[11] A.D. Graham, The study of fatigue crack growth in high strength steels using electron microscopy techniques, structures and materials, ARL technical memorandum 219, aeronautical research laboratory, November; (1973).

[12] N.T. Goldsmith and G. Clark, Analysis and interpretation of aircraft component defects using quantitative fractography. In: Strauss BM, Putatunda SK, editors. Quantitative methods in fractography, ASTM STP, 1085. Philadelphia: American Society for Testing and Materials; (1990).

DOI: 10.1520/stp23534s

[13] W. Zhuang and L. Molent, Block-by-block approaches for spectrum fatigue crack growth prediction, Engineering Fracture Mechanics, 75 (2008) 4933-4947.

DOI: 10.1016/j.engfracmech.2008.06.033

[14] S.A. Barter, Fatigue Crack Growth in 7050-T7451 Aluminium Alloy Thick Section Plate with a Surface Condition Simulating Some Regions of F/A-18 Structure, DSTO-TR-1458, Defence Science and Technology, Australia, (2003).

[15] G.J. Kaufman, Introduction to Aluminum Alloys and Tempers. ASM International, (2000).

[16] FAA - Metallic Materials Properties Development and Standardization (MMPDS), the Federal Aviation Administration (FAA), (2006).

[17] W. Zhuang, Q. Liu and W. Hu, The effect of specimen thickness on fatigue crack growth rate and threshold behaviour in aluminium alloy 7075-T7351, Proceedings of 6th Australasian Congress on Applied Mechanics, ACAM 6, Perth Austral, 12-15 December (2010).