Doctor of Philosophy
Department of Materials Engineering
Smiltnieks, Shane, Fatigue strength of adhesively bonded aluminium in a marine environment, Doctor of Philosophy thesis, Department of Materials Engineering, University of Wollongong, 2002. http://ro.uow.edu.au/theses/1496
Adhesives are being used for the joining of both semi-structural and structural components at an ever increasing rate. This increase in use is related directly to the acknowledgment of the many advantages adhesives have over more conventional methods of bonding. There are though, a number of industries that are sceptical of the long term performance of adhesives and hence their use has been kept to a minimum. One of these industries is the aluminium shipbuilding industry where long term durability is very important. jAluminium vessels are exposed to continual cyclic stresses and the harsh environment of both the sun and saltwater. This project has brought about the development of a testing facility, which allows the simultaneous fatigue testing hostile environment exposure of adhesively bonded joints. Studies have also been aimed at developing pretreatment systems, which assist in providing satisfactory fatigue performance. Lap shear tests were used initially to determine the effect of the various pretreatment/adhesive combinations and the effect of a hostile sodium chloride solution on joint strengths. Those combinations that proved to be effective in increasing joint strength or exhibited unexpected results where then tested using the fatigue rig. A number of these combinations where then fatigue tested while under the simultaneous effect of a salt spray environment. Once failure had occurred, extensive surface characterisation utilising techniques such as Atomic Force Microscopy, Optical Microscopy, X-Ray Photoelectron Microscopy and Transmission Electron Microscopy where investigated to determine the mechanism of joint failure. The various studies showed that both the joint strength and the durability of the joint under a hostile environment could be increased by several orders of magnitude with correct selection both adhesive and pretreatment. The use of the Width Tapered Cantilever Beam type fracture mechanics specimen was also investigated in conjunction with an analytical model to determine if the two could be used to predict the fatigue strength of adhesively bonded joints both under an ambient, and a hostile salt spray environment. Good correlation was found between the experimentally determined results and those obtained using the analytical model, indicating that this method may have potential in determining results rapidly which under normal experimental conditions may take from several months to years to obtain.