The Effect of Peening on the Fatigue Life of 7050 Aluminium Alloy

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Published by DSTO Aeronautical and Maritime Research Laboratory 506 Lorimer St Fishermans Bend Victoria 3207 Telephone: (03) 9626 8111 Fax: (03) 9626 8999 © Commonwealth <strong>of</strong> Australia 2001 AR No. 011-795 March 2001 Conditions <strong>of</strong> Release and Disposal This document is the property <strong>of</strong> the Australian Government; the information it contains is released for defence purposes only and must not be disseminated beyond the stated distribution without prior approval. <strong>The</strong> document and the information it contains must be handled in accordance with security regulations applying in the country <strong>of</strong> lodgement, downgrading instructions must be observed and delimitation is only with the specific approval <strong>of</strong> the Releasing Authority as given in the Secondary Distribution statement. This information may be subject to privately owned rights. <strong>The</strong> <strong>of</strong>ficer in possession <strong>of</strong> this document is responsible for its safe custody. When no longer required DSTO Reports should be returned to the DSTO Library, (Reports Section), Salisbury SA.
<strong>The</strong> <strong>Effect</strong> <strong>of</strong> <strong>Peening</strong> on the Fatigue Life <strong>of</strong> 7050 Aluminium Alloy Executive Summary Many changes in the design and manufacture <strong>of</strong> high-performance military aircraft ⎯ for example, the use <strong>of</strong> highly optimised design and the use <strong>of</strong> higher-strength materials ⎯ have led to an increased sensitivity <strong>of</strong> airframe fatigue life to surface features such as corrosion or mechanical damage. <strong>The</strong> peening applied to the F/A-18 represents a significant departure from traditional manufacture, and it is therefore important that the RAAF and AMRL have a thorough understanding <strong>of</strong> the peening process, the surface conditions produced, and their effect on structural integrity. To build the required level <strong>of</strong> understanding, AMRL has undertaken a number <strong>of</strong> research programs, over nearly ten years, investigating the effects <strong>of</strong> glass bead peening on the aluminium alloy 7050 used in RAAF F/A-18 aircraft. <strong>The</strong> overall aim <strong>of</strong> the peening research and development discussed was to establish a Life-Improvement- Factor (LIF) for the peening used on the F/A-18, as well as any future peening required by modifications. It also attempted to provide a means <strong>of</strong> measuring peening quality, to allow the full exploitation <strong>of</strong> peening to improve fatigue life. From this research came methods <strong>of</strong> surface peening and methods <strong>of</strong> surface removal, which allowed development <strong>of</strong> localised life extension methods for the airframe. <strong>The</strong>se life extension methods are now being applied in full-scale fatigue tests (to keep tests going after initial failures) and are likely to be applied to both RAAF and CF fleet aircraft. This report discusses the fatigue crack growth research at AMRL, and elsewhere, relating to peening <strong>of</strong> aluminium alloys, and summarises the improvements in peening which have arisen from this research. It also highlights areas where further research could be beneficial in relation to peening and the structural integrity <strong>of</strong> the F/A-18 aircraft. It highlights the practical problems <strong>of</strong> introducing changes to fatigue critical surfaces, with particular reference to the RAAF and CF fleets.
Page 1: The Effect
Page 7: Contents 1. INTRODUCTION ..........
Page 10 and 11: DSTO-RR-0208 extension method has n
Page 12 and 13: DSTO-RR-0208 Figure 2: A graph illu
Page 14 and 15: DSTO-RR-0208 the total life is long
Page 16 and 17: DSTO-RR-0208 Figure 4: This figure
Page 18 and 19: DSTO-RR-0208 Figure 6: The<
Page 20 and 21: DSTO-RR-0208 Figure 8: The<
Page 22 and 23: DSTO-RR-0208 crack initiate from an
Page 24 and 25: DSTO-RR-0208 Figure 10: SEM photogr
Page 26 and 27: DSTO-RR-0208 550 USN Spectrum (ST-1
Page 28 and 29: DSTO-RR-0208 Table 2: Four point be
Page 30 and 31: DSTO-RR-0208 Figure 15b: Scanning e
Page 32 and 33: DSTO-RR-0208 Research by Fair et al
Page 34 and 35: DSTO-RR-0208 3.2.3 Summary
Page 36 and 37: DSTO-RR-0208 Peak Spectrum Stress (
Page 38 and 39: DSTO-RR-0208 Figure 21b: A typical
Page 40 and 41: DSTO-RR-0208 10 Crack Depth (mm) 1
Page 42 and 43: DSTO-RR-0208 Table 7: The</
Page 44 and 45: DSTO-RR-0208 200 180 160 8A ALMEN 6
Page 46 and 47: DSTO-RR-0208 Figure 28: A schematic
Page 48 and 49: DSTO-RR-0208 Table 9: Residual Stre
Page 50 and 51: DSTO-RR-0208 Like all the structura
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DSTO-RR-0208 Y470 X19 pocket Peened
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DSTO-RR-0208 4. Discussion
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DSTO-RR-0208 5. Conclusion 1. <stro
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DSTO-RR-0208 Clayton J.Q. and Clark
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DSTO-RR-0208 Sharp P.K. and Clark G
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DSTO-RR-0208 Figure 23: The
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DSTO-RR-0208 A.4. Surface Roughness
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UK Defence Research Information Cen
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Page classification: UNCLASSIFIED D
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The Effect of Peening on the Fatigue Life of 7050 Aluminium Alloy

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