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US/Australia Collaborative Research Project on Corrosion Fatigue in D6AC Steel Joints

Report Number: AFML TR 78-150
Author: Harmsworth, C. L.
Author: Kemsley, D. S.
Author: Finney, J. M.
Corporate Author: Air Force Materials Laboratory
Laboratory: Air Force Materials Laboratory
Date of Publication: 1978-12
Pages: 100
Project: 2418
Task: 241807
AD Number: ADA076197

A U.S./Australian Program has been conducted to determine the effect of manufacturing-induced and environmental corrosion on D6AC steel Taper-Lok bolted joints as used in the F-111 aircraft. Under constant amplitude, traces of distilled water or concentrated hydrochloric acid in the bolt holes did not reduce fatigue life. Under spectrum loading traces of water did not affect fatigue life but traces of hydrochloric acid reduced the mean fatigue life of the joint by a factor of 110. The results of further constant amplitude tests and a limited series of spectrum tests confirmed previous findings that the life of those original joints in the F-111 which were manufactured using a six-flute hand reamer could be appreciably extended by rework with an 18-flute tapered reamer as used in later F-111 production. Other rework procedures involving cold working of the hole by a mandrel or specially designed fasteners showed little improvement when used in this relatively high-strength steel joint material. The effects of improved sealants and the capability of ultrasonic and magnetic NDI techniques for inspection of cracks at fastener holes were also investigated. It is concluded that the life of uncontaminated, properly fabricated and sealed D6AC steel joints as used in the F-111 wing carry through should not be a source of fatigue failure during a normal aircraft lifetime.

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