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BY 4.0 license Open Access Published by De Gruyter May 26, 2013

Utilising CODmax as an Indirect Fatigue Crack Length Measurement Parameter for M(T) Specimens of an Airframe Aluminium Alloy AA6056

  • Waman Vishwanath Vaidya , Manfred Horstmann , Kandasamy Angamuthu and Mustafa Koçak
From the journal Materials Testing

Abstract

Accuracy of indirect fatigue crack length measurement by potential drop method or by compliance technique may be affected at low load ratio due to fracture surface contact, crack closure or mixed mode fracture. As an alternative, the maximum value of crack opening displacement, CODmax, from a clip gauge was utilized. Middle crack tension M(T) specimens were used to obtain conservative data at a low load ratio (R = 0.1). Thin sheet specimens (B = 3.2 mm) with different widths (100 mm ≤ W ≤ 400 mm) of AA6056-T4 were investigated in the mid-regime (Paris regime), which is of interest for damage tolerance analysis. The use of CODmax is found to provide crack lengths equivalent to those measured optically. Hence, the method is very suitable for indirect crack length measurement. Furthermore, small width specimens provided data equivalent to large width specimens. Insofar, the size effect is found to be absent, and fatigue crack propagation data can be acquired on small width specimens when material availability is limited.

Kurzfassung

Anwendung der maximalen Rissoffnungsverschiebungswerte fur die indirekte Risslangenmessung bei der Ermudungsrissausbreitung an mittig angerissenen Zugproben der luftfahrtspezifischen Aluminiumlegierung AA6056. Bei der Ermudungsrissausbreitung kann wegen Bruchflachenberuhrung oder Rissschliesung bei einem niedrigen Krafteverhaltnis sowie des Scherbruchs die Genauigkeit der indirekten Risslangenmessung durch die Potenzialmethode oder die Nachgiebigkeit (Compliance) beeinflusst werden. Als Alternative wird der Maximalwert der Rissoffnungsverschiebung, CODmax, genutzt. Es wurden mittig angerissene Zugproben, M(T)-Proben, verwendet, um konservative Rissausbreitungsdaten bei einem niedrigen Kraftverhaltnis (R = 0,1) zu erhalten. Dunne Blechproben (B = 3,2 mm) mit unterschiedlichen Breiten (100 mm ≥ W ≥ 400 mm) aus AA6056-T4 wurden im mittleren Rissausbreitungsbereich (Paris- Bereich), der fur die Schadenstoleranzanalyse von Interesse ist, untersucht. Der Gebrauch von CODmax. Werten lieferte indirekte Risslangen, die nahrungsweise identisch mit den optisch-gemessenen Risslangen waren. Weiterhin wurde festgestellt, dass die gelieferten Daten der Proben mit kleinen Breiten denen der grosen Probenweiten entsprachen. Insofern ist der Groseneffekt vernachlassigbar und die Rissfortschrittsdaten von den kleinen Probenbreiten konnen ebenso genutzt werden, wenn nicht genugend Material fur die grosen Proben zur Verfugung steht.


Dr.-Ing. Waman Vishwanath Vaidya, born in 1944, earned his Bachelor and Master of Engineering in Metallurgy from the University of Poona, India, and his Ph.D. from the University of Karlsruhe (TH), Germany. He worked at the College of Engineering, Poona, in various foundries of Rheinstahl AG and at the Nuclear Research Centre, Karlsruhe, before joining the GKSS Research Centre in 1980. He has worked on precipitation, recrystallisation, radiation damage, and fatigue crack propagation threshold. Since last few years he has been working on Al-alloy welds for airframes.

Dipl.-Phys. Manfred Horstmann, born in 1953, studied Physical Technology at the Lübeck University of Applied Sciences, Germany. In 1979 he joined testing laboratories for civil aircrafts at MBB, Hamburg-Finkenwerder. Since 1982 he is working at the GKSS Research Centre and involved in fatigue experiments.

Dr. Kandasamy Angamuthu, born in 1964, studied Mechanical Engineering during graduation, Welding Engineering for post-graduation and earned his Ph.D. from the Indian Institute of Technology, Madras, India. He worked in different engineering colleges at home and abroad, and has research and academic experience of more than twenty years in the area of fatigue and fracture. He was at GKSS Research Centre as a postdoctoral scholar from 2001 to 2004, and worked on welded aerospace Al-alloys. He is now with Sherwood College of Engineering, Barabanki, India.

Dr. Mustafa Koçak, born in 1953, studied Mechanical Engineering at the Middle East Technology University, Ankara, Turkey, and earned his Ph.D. from the University of Bath, UK. He worked at the University of Liverpool, UK, before joining GKSS Research Centre in 1984. Since then he was engaged in experimental and analytical fracture mechanics with particular emphasis on welds on national and international levels. He has been working also on laser beam welding of Al-alloys. He is now CEO of the GEDIK Holding, Istanbul, Turkey and works in the fields of welding and casting.


Refrences

1 W. G.Clarkjr., S. J.Hudakjr.: Variability in fatigue crack growth testing, J. Test. Eval.3 (1975), pp. 454476Search in Google Scholar

2 C. J.Beevers (Ed.): The Measurement of Crack Length and Shape During Fracture and Fatigue, Engineering Materials Advisory Service (EMAS), West Midlands, UK (1980)Search in Google Scholar

3 S. J.Hudakjr., R. J.Bucci (Eds.): Fatigue Crack Growth Measurement and Data Analysis, ASTM STP 738, American Society for Testing and Materials, Philadelphia, USA (1981)Search in Google Scholar

4 K. J.Marsh, R. A.Smith, R. O.Ritchie (Eds.): Fatigue Crack Measurement: Technique and Applications, Engineering Materials Advisory Service (EMAS), West Midlands, UK (1991)Search in Google Scholar

5 ASTM Standard E647: Standard test method for measurement of fatigue crack growth rates, Annual Book of ASTM Standards, Section Three: Metals Test Methods and Analytical Procedures, Volume 03.01: Metals-Mechanical Testing, Elevated and Low-Temperature Tests, Metallography, ASTM International, West Conshohocken, PA, USA (2005), pp. 628670Search in Google Scholar

6 R.Bowman, S. D.Antolovich, R. C.Brown: A demonstration of problems associated with crack closure measurement techniques, Engng. Fract. Mech.31 (1988), pp. 703712Search in Google Scholar

7 R. L.Hewitt: Accuracy and precision of crack length measurements using a compliance technique, J. Test. Eval.11 (1983), pp. 15015510.1520/JTE10284JSearch in Google Scholar

8 M. E.Fine, J. L.Horng, D. H.Park: Effect of microstructure and specimen geometry on crack propagation threshold, C. J.Beever (Ed.): Fatigue 84, Proceedings of the Second International Fatigue Congress, Engineering Materials Advisory Service (EMAS), West Midlands, UK (1984), pp. 739748Search in Google Scholar

9 R. S.Veccio, J. S.Crompton, R. W.Hertzberg: The influence of specimen geometry on near threshold crack growth, Fatigue Fract. Engng. Mater. Struct.10 (1987), pp. 332342Search in Google Scholar

10 P.Hutar, S.Seitl, Z.Knésl: Quantification of the effect of specimen geometry on the fatigue crack growth response by two–parameter fracture mechanics, Mater. Sci. Engng. A, 387-389 (2004), pp. 491494Search in Google Scholar

11 R.Hamam, S.Pommier, F.Bumbieler: Variable amplitude fatigue crack growth, experimental results and modeling, Int. J. Fatigue, 29 (2007), pp. 16341646Search in Google Scholar

12 S.Seitl, P.Hutar, Z.Knésl: Sensitivity of fatigue crack growth data to specimen geometry, Key Engng. Mater.385-387 (2008), pp. 557560Search in Google Scholar

13 W. V.Vaidya, M.Horstmann, K.Angamuthu, M.Koçak: Parametric (non)-variance of the mid-regime fatigue crack propagation in an aluminium alloy AA6056-T6, MP Mater. Test.52 (2010), pp. 300305Search in Google Scholar

14 J.Schijve: Shear lips on fatigue fractures in aluminium alloy sheet materials, Engng. Fract. Mech.14 (1981), pp. 78980010.1016/0013-7944(81)90091-6Search in Google Scholar

15 J. M.Barsom: The dependence of fatigue crack propagation on strain energy release rate and crack opening displacement, M. S.Rosenfeld (Ed.): Damage Tolerance in Aircraft Structures, ASTM STP 486, ASTM, Philadelphia, USA (1971), pp. 11510.1520/STP26670SSearch in Google Scholar

16 R. O.Ritchie: Incomplete self-similarity and fatigue crack growth, Int. J. Fract.132 (2005) pp. 197203.10.1007/s10704-005-2266-ySearch in Google Scholar

17 P. C.Paris, M. P.Gomez, W. E.Anderson: A rational analytical theory of fatigue, The Trend in Engineering, 13 (1961), pp. 914Search in Google Scholar

18 R. J. H.Wanhill: Damage tolerance engineering property evaluations of aerospace aluminium alloys with emphasis on fatigue crack growth, Report, NLR TP 94177 U (1995)Search in Google Scholar

19 H. K.Sriharsha, R. K.Pandey, S.Chatterjee: Towards standardising a sub-size specimen for fatigue crack propagation behaviour of a nuclear pressure vessel steel, Engng. Fract. Mech.24 (1999), pp. 607624Search in Google Scholar

20 S.Ravi, V.Balasubramanian, S.Nemat Nasser: Effect of mis-match ratio (MMR) on fatigue crack growth behavior of HSLA steel welds, Engng. Fail. Anal.11 (2004), pp. 413428Search in Google Scholar

21 M.Horstmann, J. K.Gregory, K.-H.Schwalbe: The AC potential drop method, Materialprufung35 (1993), pp. 212217Search in Google Scholar

22 W. V.Vaidya: Fatigue threshold regime of a low alloy ferritic steel under closure-free testing conditions: Part I-compliance variations in the threshold regime, J. Test. Eval.20 (1992), pp. 15716710.1520/JTE11709JSearch in Google Scholar

23 W. V.Vaidya: Inference on the bulk response of a long crack to fatigue loading, Scr. Metall. Mater.26 (1992), pp. 29730210.1016/0956-716X(92)90190-PSearch in Google Scholar

24 A. M.Sullivan, T. W.Crooker: A crackopening displacement technique for crack length measurement in fatigue crack growth rate testing- development and evaluation, Engng. Fract. Mech.9 (1977), pp. 159166Search in Google Scholar

25 R.Dif, B.Bes, T.Warner, P.Lequeu, H.Ribes, P.Lassince: Recent developments in AA6056 aluminium alloy used for aerospace, in: M.Tiryakioglu (Ed.), Advances in the Metallurgy of Aluminium Alloys, ASM International, Materials Park, USA (2001), pp. 390398Search in Google Scholar

26 R.Kocik, T.Vugrin, T.Seefeld: Laser beam welding in airframe structures, status and future applications (in German), F.Vollertsen, T.Seefeld (Eds.): Laserstrahlfügen: Prozesse, Systeme, Anwendungen, Trends, Strahltechnik, Band 28, BIAS-Verlag, Bremen, Germany (2006), pp. 1526Search in Google Scholar

27 W. V.Vaidya, K.Angamuthu, M.Koçak: Effect of load ratio and temper on fatigue crack propagation behaviour of Al-alloy AA6056, A. F.Blom (Ed.), Fatigue 2002, Proceedings of the Eighth International Fatigue Congress, Engineering Materials Advisory Service (EMAS), West Midlands, UK (2002), pp. 14671474Search in Google Scholar

28 K.-H.Schwalbe, D.Hellmann: Application of electrical potential method to crack length measurements using Johnson's formula, J. Test. Eval.9 (1981), pp. 218221Search in Google Scholar

29 W. V.Vaidya, M.Koçak, M.Horstmann, V.Ventzke, M.Pakdil, J.Hackius: Effect of porosity on fatigue crack propagation behaviour of a laser beam welded aluminium alloy, Fatigue Design 2005, Proceedings of the International Conference, CETIM – Centre Technique des Industries Mécaniques (French Industrial and Mechanical Technical Centre), Senlis, France (2007), ISBN 2-85400-711-9, on CD ROMSearch in Google Scholar

30 W. V.Vaidya, M.Horstmann, E.Seib, K.Toksoy, M.Koçak: Assessment of fracture and fatigue crack propagation of laser beam and friction stir welded aluminium and magnesium alloys, Adv. Eng. Mater.8 (2006), pp. 399406Search in Google Scholar

31 W. V.Vaidya, M.Horstmann, V.Ventzke, B.Petrovski, M.Koçak, R.Kocik, G.Tempus: Structure-property investigations on a laser beam welded dissimilar joint of aluminium AA6056 and titanium Ti6Al4V for aeronautical applications, Part II-Resistance to fatigue crack propagation and fracture, Mat.-wiss. u. Werkstofftech.40 (2009) pp. 769779Search in Google Scholar

Published Online: 2013-05-26
Published in Print: 2010-11-01

© 2010, Carl Hanser Verlag, München

This work is licensed under the Creative Commons Attribution 4.0 International License.

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