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The investigation contained herein is a part of a larger, long-term project: The Development of SMART Aircraft Bolts. Structural failures, at highly stressed components, arc common in some of the aircraft used by the South African Air force. The strength of one such component, the wing bolts on the C-130 aircraft, is analysed and compared to the stress distribution in a bolt which has a small hole drilled through the centre of the bolt (which will be used to insert a sensing device). The results of this analysis will be used as input into further phases of the project, e.g., SMART material selection and the development of sensing devices. Due to the complex physics of a bolted joint, advanced analysis of the bolt under conservative loading was performed, after conducting thorough research into bolted joint design and analysis methods, in order to provoke the final recommendations. / Thesis (M.Sc.)-University of Natal, Durban, 2000.

Aviation is known to have some of the most stringent structural health monitoring standards in the world. An example of this would be the fact that certain bolts in the aircraft assembly must be periodically removed and inspected for fatigue damage. This can be a very costly endeavour: a case in point being the Hercules C130 aircraft, which requires approximately 200 man hours of down-time for the inspection of the bolts that attach the wings to the fuselage. The substitution of TRIP (Transformation Induced Plasticity) steel bolts for the current HSLA steel (AISI 4340) from which the bolts are manufactured, allows the bolt to act in the capacity of load bearing member as well as damage detector. This unique feature is a consequence of the transformation characteristic exhibited by TRIP steels when they are strained: an irreversible change within their microstructure from paramagnetic austenite parent phase to permanent ferromagnetic state occurs in direct proportion to the peak strain. This property allows us to establish a relationship from which the service life of the component can be determined. A prototype of a smart aircraft bolt and washer system has been developed, where the bolt acts as damage detector and the washer effectively examines the health of the bolt by reading the changing magnetic susceptibility of the bolt. This study presents both material development and product development phases of the Smart Aircraft Bolt prototype. A prediction of transformation characteristic due to deformation is carried out using finite element analysis (mechanical model) and a constitutive model (strain induced martensitic transformation kinetics) to predict the best situation for the smart washer. In addition, experimental work is performed in the form of cyclic temperature testing (with and without external loading) and tension-tension fatigue testing. For both sets of experimental testing, two positions of washer placement are tested. A correlation between volume fraction of martensite present and remaining life, is therefore possible. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2008.