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The investigations described in this paper were conducted to develop new fasteners and joining methods to reduce the weight and improve the fatigue life of aircraft structures. Three major modes of structural failure—fatigue, fretting, and stress corrosion—are discussed along with recommendations for improvement. Stresscoining was developed to cold-work aircraft structures for fatigue improvement. Fretting fatigue failures have been reduced by using Teflon coatings on fasteners and in faying surfaces of splice joints. Standard stress corrosion test blocks have been designed for evaluation of this failure mode. A crown flush rivet configuration has been developed that does not require head shaving after installation. Qualification tests were performed in compliance with MIL-STD-1312 to obtain Federal Aviation Administration and military approval.
Various new fasteners have been developed for aluminum, carbon-fiber composite, and titanium structures. These fasteners were designed to be “forgiving to the hole” in that they fill and prestress the hole uniformly without being extremely sensitive to hole-preparation tolerances. New low-cost specimens have been designed to provide a basis for screening and comparing fastener tests conducted by fastener manufacturers and aircraft companies. These programs are directed toward creating technology for achieving a more balanced fatigue-resistant aircraft structure.
fatigue life, fretting, stress corrosion, fasteners, joining methods, stress-coining, weight reduction
Senior structural design engineer, Douglas Aircraft Co., Long Beach, CA