published_or_final_version / Civil Engineering / Master / Master of Philosophy

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

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No description available.

The use of fibre composites in the design of load carrying aircraft structures has been increasing over the last few decades. At the same time, aluminium alloys are still present in many structural parts, which has led to an increase of the number of hybrid composite-aluminium structures. Often, these materials are joined at their interface by bolted connections. Due to their different response to thermal, mechanical and environmental impact, the composite and the aluminium alloy parts are subject to different design and certification practices and are therefore considered separately.The current methodologies used in the aircraft industry lack well-developed methods to account for the effects of the mismatch of material properties at the interface.One such effect is the thermally induced load which arises at elevated temperature due to the different thermal expansion properties of the constituent materials. With a growing number of hybrid structures, these matters need to be addressed.  The rapid growth of computational power and development of simulation tools in recent years have made it possible to evaluate the material and structural response of hybrid structures without having to entirely rely on complex and expensive testing procedures.However, as the failure process of composite materials is not entirely understood, further research efforts are needed in order to develop reliable material models for the existing simulation tools. The work presented in this dissertation involves modelling and testing of bolted joints in hybrid composite-aluminium structures.The main focus is directed towards understanding the failure behaviour of the composite material under static and fatigue loading, and how to include this behaviour in large scale models of a typical bolted airframe structure in an efficient way. In addition to that, the influence of thermally induced loads on the strength and fatigue life is evaluated in order to establish a design strategy that can be used in the industrial context. The dissertation is divided into two parts. In the first one, the background and the theory are presented while the second one consists of five scientific papers.

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The present thesis investigates the friction properties of total knee replacement components using lubricating fluids of different composition and rheology. The first stage of the thesis involves characterization of the rheological properties of hyaluronic acid (HA)/bovine calf serum (BCS) solutions. With increased concentration and molecular weight of HA, higher viscosities and more pronounced shear thinning in steady shear flow was observed. In dynamic oscillatory flow, the elastic character of the solutions became more pronounced and the cross-over frequency decreased upon increasing concentration and molecular weight of HA. The second part of the thesis involves the determination of a method by which the coefficient of friction is estimated using a linear reciprocating wear testing machine with spherical metal indenters articulating on flat UHMWPE samples and deionised (D.I.) water lubrication. A characteristic periodic pattern in the friction behaviour was observed and the coefficient of friction was computed by calculating the average of 30 points about the midpoint between reversals and using the average of three cycles. The third part of the thesis involves the investigation of the effect of fluid composition on the coefficient of friction in knee replacement components. With increased concentration of HA in solution (0-1mg/mL), the coefficient of friction of HA/BCS solutions decreased. However, with HA/BCS solutions of higher HA concentrations (above 1mg/mL), no significant difference in the coefficient of friction was observed. Similar behavior was observed with HA/Albumin solutions. With HA/ D.I. water solutions, the coefficient of friction was almost identical irrespective of the concentration of HA in solution. Significant difference in the rheological properties of HA/D.I. water solutions did not affect the coefficient of friction. The Stribeck analysis revealed that the coefficient of friction with HA/BCS and HA/D.I. water lubrication was not governed by hydrodynamic conditions. The fourth part of this thesis involved characterization of lubricating fluids before and after friction testing. Absorbance and dynamic light scattering measurements of HA/BCS solutions and of HA/Albumin solutions indicate a rise in turbidity and the presence of larger size particles in these solutions after friction testing. The ninhydrin test confirmed the presence of protein in the precipitates obtained following testing. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2010-09-24 14:06:41.437

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Empirical and modelling studies are reported which explore ways in which the central nervous system might consider musculo-skeletal geometry when generating commands for single degree of freedom elbow flexion and extension movements. In a series of experiments it is shown that subjects do not perform rapid, goal-directed flexion and extension movements equally accurately in different parts of the elbow's workspace. In these experiments, movements of 10, 20 and 30 degrees in amplitude were tested using up to five different initial elbow angles. When performing flexions, subjects tended to overshoot targets when starting from extended positions, to undershoot targets when starting from more flexed positions, and to perform relatively accurate movements when starting from the centre of the workspace. Final position accuracy was more variable for extensions. When reliable differences existed for extensions, subjects tended to produce a pattern of results opposite to that of flexions: subjects overshot targets when starting from flexed positions and undershot targets when starting from more extended positions. A model of elbow movement based on the $ lambda$ version of the equilibrium-point hypothesis was used to assess the extent to which the pattern of errors obtained in the empirical studies could be reproduced by a control scheme that does not adjust commands in response to changing musculo-skeletal geometry, but rather uses one single invariant command throughout the workspace. The motivation for testing the invariant command notion was to explore the possibility that motion planning might be achieved without an explicit representation of musculo-skeletal geometry. Predicted patterns of final position errors across the workspace matched empirically obtained error patterns for flexions, but the model performed less well when predicting the pattern of errors observed for extension movements.