Four Point Bending Fatigue Tests of Forged Ti 6Al 4V

Bernd Oberwinkler; Martin Riedler; Heinz Leitner; Ataollah Javidi

doi:10.3139/120.110038

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Four Point Bending Fatigue Tests of Forged Ti 6Al 4V

Bernd Oberwinkler , Martin Riedler , Heinz Leitner und Ataollah Javidi

Veröffentlicht/Copyright: 28. Mai 2013

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Aus der Zeitschrift Materials Testing Band 51 Heft 9

Abstract

The paper derives from a long-term research program that is aimed at developing qualitative and quantitative design guidelines to influence mechanical surface treatments in order to improve the fatigue life of structural components. A four point bending test rig was developed using finite element analysis. High cycle fatigue tests were performed on plane specimens taken from Ti 6Al 4V forgings with mill-annealed or bimodal microstructure. The high cycle fatigue behaviour of specimens with two different surface conditions (as-forged and machined) was compared. In order to assess the fatigue failure mechanisms, detailed investigations of the surface layer were carried out. Residual stresses were shown to play an important role in fatigue.

Kurzfassung

Insbesondere auf dem Gebiet des Flugzeugbaus setzt man bei Strukturteilen bevorzugt auf geschmiedete Bauteile, wobei als Werkstoff oftmals Ti-6Al-4V zur Anwendung kommt. Das Ermüdungsverhalten solcher Komponenten wird dabei maßgeblich durch die Oberflächenbeschaffenheit beeinflusst, wobei der Schwerpunkt dieser Forschungsarbeit auf dem Vergleich von schmiederoher und gefräster Oberfläche liegt. Dazu wurden Vierpunkt-Biegeschwingversuche an Flachproben aus Ti-6Al-4V mit bimodaler bzw. mill-geglühter Mikrostruktur durchgeführt. Es zeigten sich aufgrund der unterschiedlichen Oberflächenzustände insbesondere im Bereich der Zeitfestigkeit große Unterschiede in der Schwingfestigkeit. Die Randschichten der jeweiligen Oberflächenzustände wurden charakterisiert, wobei sich zeigte, dass der vorliegende Eigenspannungszustand die Schwingfestigkeit entscheidend beeinflusst.

Dipl.-Ing. Bernd Oberwinkler, born in 1984, studied Mechanical Engineering at the University of Leoben (Austria). Since 2007 he has been scientific assistant and PhD student at the Institute of Mechanical Engineering at the University of Leoben.

Dr. Martin Riedler, born in 1975, studied Mechanical Engineering at the University of Leoben (Austria). From 2001 until 2006 he was scientific assistant at the Institute of Mechanical Engineering at the University of Leoben and finished his PhD in 2005. Since 2006 he has been working at Böhler Schmiedetechnik GmbH & Co KG in Kapfenberg (Austria) in research and development. There he is responsible for thermo-mechanical process development (forging and heat treatment), and fatigue analysis projects of aerospace parts.

Dr. Heinz Leitner, born in 1970, studied Mechanical Engineering at the University of Leoben (Austria). From 1998 until 2001 he was scientific assistant at the Institute of Mechanical Engineering at the University of Leoben and finished his PhD in 2001. From 2002 until 2005 he worked as key researcher at the Christian Doppler Laboratory for Fatigue Analysis at the University of Leoben. Since 2006 he has been head of Experimental Fatigue at the Institute of Mechanical Engineering at the University of Leoben.

Dr. Ataollah Javidi, born in 1970, studied Mechanical Engineering at the University of Leoben (Austria). Since 2003 he has been scientific assistant at the Institute of Mechanical Engineering at the University of Leoben and finished his PhD studies in 2008.

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Published Online: 2013-05-28

Published in Print: 2009-09-01

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https://doi.org/10.3139/120.110038