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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


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.


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.


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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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