Abstract
This paper presents results from tests aimed to assess the relative ductility of titanium alloy Ti 6Al-4V and stainless steel A286 aerospace fasteners of comparable size and tensile strength. A test procedure is developed, and tensile tests are performed on test fasteners. All test fasteners fracture in the threaded region. Elastic and plastic deformation at rupture are extracted from the resulting load versus displacement curves and used to compute the ductility index for each test fastener. The ductility index quantifies the relative ductility between the different fastener materials. The average ductility index for the titanium alloy fasteners is about one-tenth the average value for the A286 fasteners. In addition, the fracture surfaces of the titanium alloy test fasteners fracture perpendicular to the axis of tensile loading, whereas the A286 test fasteners fracture across three or four threads, which corresponds to about a 45° angle. Both the relative ductility index values and fracture surface characteristics indicate much less ductility in the titanium alloy fasteners. These results are not intended to discourage the use of titanium alloy fasteners but rather to provide additional data for use in proper joint design when the benefits of lower weight or extreme temperature use are required.
Similar content being viewed by others
References
F. Gross, Concerns with the use of titanium fasteners, NASA Materials Engineering Branch Technical Information Paper No. 133 (2003)
M. Stevenson, J. McDougall, K. Cline, Metallurgical failure analysis of titanium wing attachment bolts. ASM Int. Pract. Fail. Anal. 3, 75–80 (2003)
A. Jha, S. Singh, M. Kiranmayee, K. Sreekumar, P. Sinha, Failure analysis of titanium alloy Ti6Al4V fastener used in aerospace application. Eng. Fail. Anal. 17, 1457–1465 (2010)
NASA-STD-5020, Requirements for threaded fastening systems in spaceflight hardware (2012)
G. Gerard, Structural significance of ductility in aerospace pressure vessels. ARS J. 32, 1216–1221 (1962)
K. Samuel, Dependence of strength and ductility ratios in austenitic stainless steels. Int. J. Press. Vessels Pip. 83, 474–476 (2006)
J. Whittaker, Ductility and use of titanium alloy and stainless steel aerospace fasteners, University of South Florida, MS Thesis (2015)
ASTM F606-13, Standard test methods for determining the mechanical properties of externally and internally threaded fasteners, washers, and rivets (2013)
Acknowledgments
The authors gratefully acknowledge the funding and support of the NASA Engineering and Safety Center (NESC) and Dr. Michael Dube for this work.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Whittaker, J.T., Hess, D.P. Ductility of Titanium Alloy and Stainless Steel Aerospace Fasteners. J Fail. Anal. and Preven. 15, 571–575 (2015). https://doi.org/10.1007/s11668-015-0007-8
Received:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11668-015-0007-8