Ductility of Titanium Alloy and Stainless Steel Aerospace Fasteners
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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.
KeywordsFastener Bolt Ductility Titanium Stainless steel Aerospace Aviation
The authors gratefully acknowledge the funding and support of the NASA Engineering and Safety Center (NESC) and Dr. Michael Dube for this work.
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