Advanced ceramic materials are assuming increasing industrial importance because of their special properties. However, the extreme hardness and brittleness of these materials make their machining efficiency low. The difficulty arises from shaping ceramics whilst conserving their surface integrity, strength and high quality surface finish. Manufacturing processes such as grinding with diamond bonded wheels present one solution. The use of a diamond grinding wheel on the surface of ceramics, creates a complex system of elastic/plastic deformation, and subsequent cracking. For ceramic materials such as silicon nitride, two types of damage can occur; firstly surface damage in the form of machining marks which cause stress concentrations and surface cracks and secondly sub-surface cracking. These problems caused a major delay in the utilisation of these materials in the aeronautics industry. This research was aimed at providing a better understanding of the grinding process and parameters involved in machining ceramic component. An extensive preliminary study was carried out to understand the behaviour of advanced ceramic material during grinding. The effect of very high infeed and grinding wheel parameters were studied as an initial investigation. A system for on line detection of grinding wheel surface condition during grinding was developed during this research. Acoustic emission AE technique to monitor the wheel condition was also investigated during the experimental work. The grinding machine used is a commercially available machine with a stiffness coefficient of 18.5 N/μm. The machine was modified to accommodate a higher feed rate. The purpose of using this machine was to investigate how a commercial machine would grind hard material such as advanced ceramics and what the effect would be on the process of crack initiation and propagation during grinding. The effect of different grinding wheel and machine tool parameters on crack initiation and propagation was investigated and represent the main concern of this research. Experimental design using modified L27 orthogonal array was used. The response of the surface roughness, fracture strength, AE spectral amplitude, grinding forces, grinding energy, crack size, sub-surface cracks distance from the ground surface, depth of surface damage due to different grinding wheel and machine parameters used in the fractional factorial array were all investigated. Three basic types of cracks that were found to occur after the passage of an abrasive grain on the surface of ceramics materials were identified. These are radial, median and lateral cracks. Only radial cracks and machine marks are visible on the surface, median and lateral cracks (parallel to the surface) are formed below the affected zone and thus not visible. The load of an individual grain and its shape on the grinding wheel surface were found to have an influence on the crack initiation and propagation. Higher damage depth on the ground surface was measured when the grain size increased or was extremely sharp. Median cracks were found to be at a deeper location from the ground surface (2-15 μm) compared with lateral cracks. The dimensions and depth of median cracks beneath a ground surface was found to increase when the levels of grinding wheel grit size, wheel bond hardness, depth of cut and table feed were increased. However, locations of lateral cracks were found not to be affected when theseparameters increased and found to occur at 2-4 μm below the surface. The median cracks were located close to the ground surface at low table feed rates compared with deeper location when the table feed rate increased. A correlation between AE, SEM and 3D data and the ground surface condition was carried out. The condition of the ground surface whether smooth or rough was identified and linked with AE signals. The link between these observations show that an increase in percentage of surface fracture is accompanied by low-amplitude long­ duration events which can be assumed as the characteristic of brittle mode grinding. This observation was confirmed by the SEM and the 3D observations. Higher AE spectral amplitude was found to be associated with smooth ground surfaces. However, sub­ surface median cracks were found for this condition. This correlation was the first reported attempt to link different experimental measurements and parameters. Different artificial cracks were initiated on ceramic specimen surfaces in both longitudinal and transverse directions using v-shaped discs. This method of initiating cracks is more realistic than that produced by a single diamond scratch. The very random nature of diamond grit shape, size and location on the surface of the wheel would alter the characteristics of a crack initiated in a real grinding process. This technique used for creating an artificial crack is the first reported attempt hitherto. The groove generation mechanism observed using SEM was almost brittle when the depth of scratch increased. At larger groove depths, a deeper locations of sub-surface median cracks were found. Grinding processes were then carried out on these cracks to investigate their propagation. The AE spectral amplitude was found to be higher for specimens ground with artificial cracks compared with specimens ground without artificial cracks. The sub-surface cracks initiated due to grinding specimens with artificial cracks were found to be at deeper locations than to those for ceramic specimens ground without artificial cracks. The effect of remaining damage depths on the ground surface on the fracture strength were also studied. Increasing the diamond grinding wheel grit sizes, wheel bond hardness and table feed were found to be the most influential factors that increase the propagation distance of the artificial cracks during grinding. A computer model based on finite element analysis package was used to study the behaviour of the ceramics in grinding. This package was used to establish a theoretical model which was validated using experimental results. Normal and tangential grinding forces from experimental work were used as input to the FE model. These forces were chosen to indicate different wheel and machine parameters. The model simulates the process of grinding by applying these forces on the surface of the ceramic specimen to study the crack initiation, propagation and their distance from the ground surface. A complete simulation for the grinding process was made including removal of material during the process.

Published work concerning the performance of coated and uncoated carbide tipped circular saw blades has been searched and reviewed. The search has shown that little similar experiments on the carbide tipped circular saw blades have been conducted. Furthermore the evidence shows that no work has been published on the application of coatings to the carbide tipped circular saw blades. Finite element analysis has been widely applied to the cutting process, but the application of finite element methods to the carbide tipped circular saw blade is still a new area of research. In this investigation the performance and life of the carbide tool both uncoated and coated were quantified by rigorous measurement. The proposed carbide properties ( composition, cobalt distribution, specific gravity, micro-structure and red hardness of carbide) have been experimentally tested. The failure modes for the carbide circular saw blades and carbide tipped saw segments have been established. In this work a novel experimental approach was used, in which TiN and TiAlN coatings were applied to the carbide tipped circular saw. A feature of this approach is that a lower coating temperature is used and yet still retains the good bonding strength between the substrate and the coating. The parameters obtained in this investigation were used as a basis in the development of a finite element model. This model was used to optimise tooth geometry and predict the failure mode with respect to temperatures and stresses. Investigation has shown that TiN and TiAlN coatings have largely enhanced the tool life in the case of cutting proposed workpiece materials. The crater wear, flank wear and large chipping have been arrested or reduced. Computer model and transverse rupture strength figure have been established. The results shows that the model used for qualitative analysis of a problem is possible and the examples conducted in the case of cutting mild steel is completely consistent with the failure modes obtained in the cutting tests.

The procedure of calculating annual machinery ownership costs from the discounted cash flows of the mortgaged capital cost, the repair and insurance charges and the resale income is extended to include the effect of loan rate and loan period on interest charges, the effect of capital allowances taking account of the actual balancing charges at the end of the period of ownership, and the effect of tax relief on the interest charges, repair costs and insurance premiums. The concept of marginal holding cost is applied to determine the optimum ownership period. The selection of tractor- plough combinations is based on the prediction of soil characteristics such as moisture content, strength, and workability, all of which influencing the assessment of plough draught and tractor power. A number of filters are used to select the appropriate and realistic tractor /implement combinations with different sizes of fully mounted plough depending on the draught, and the speed of each selected gear of the tractor. For each acceptable combina- tion of tractor and fully mounted plough determined, the costing routine is used to calculate the annual costs. The branch and bound algorithm is suitable for mixed integer solutions to the farm machinery selection problem. Machinery sets are selected simultaneously with the chosen cropping pattern on a given land area. Machinery sets are matched correctly to the tractor sizes. Four sizes of tractor are available (45 kW, 61 kW, 74 kW and 94 kW,. Field operations take place in discrete time periods during which available work days are predicted from soil type and weather records for the specific site. Cereal and root crops are distinguished by optimum sowing and harvesting date. Discrete time periods are defined in relation to these optimal dates and give rise to overlapping operations for different crops. The calculation of probability levels for available work days when operations are subject to different criteria is discussed. A single arbitrary value of 75% probability for available work days is adopted in the linear programming model for the main part of the study. Two stage processes are used to simulate available work days in each time period. The patterns generated converge on the relative frequency pattern laid down by the generating process. The range of experience is wider than that contained in the short series of 24 years historical data. The simulation model generates results suitable for stochastic dominance ranking. In a simulation experiment on a 250 ha arable farm cropping cereals and potatoes, alternative solutions are obtained by integer linear programming, the solutions being ranked according to gross revenue. Annual costs of operating farm machinery are derived from a separate costing algorithm based on the annual hours of use which are determined by the size of the task and not by the sequence of work days. After deducting the annual costs of machinery operation, the cumulative net revenue curves cross and second order stochastic dominance ranking is used to identify the optimum (maximum profit) solution. The current study demonstrates the viability of the analytical procedures but further work is now required to reduce the computing time involved for the complete machinery selection procedure. Meanwhile, a commercial software package is prepared on the calculation of annual machinery ownership costs.

Experimental and theoretical studies of the influence of oil supply pressure on the friction torque in plain bearings have been carried out. The focus of the work has been the reduction in bearing friction that might be achieved by reducing oil supply pressure and the mechanisms by which the changes in friction occur, with potential applications to reducing bearing friction in internal combustion engines. A single bearing test rig has been used to investigate the impact of feed oil pressure on the extent of cavitation and the role of increased film cavitation on friction under light, steady loads for a bearing with a 180° groove, using an SAE 5W-30 oil. Film visualization shows that cavitation area increases when the oil feed pressure is reduced and the extent of the full width film reduces primarily as the angle of film reformation is retarded. Both load and speed increases reduce the full width film extent. At constant film viscosity, friction torque was reduced by up to 20% by increased cavitation which reduced the film area and the eccentricity ratio. The latter reduces the surface shear stress in the load-bearing region of the film and overall, the circumferential average. As load increases, the reduction in film area accounts for an increasing proportion of the friction torque reduction. The effect of load, speed, lubricant formulation and clearance on bearing friction and film pressure has been investigated. Increases in load led to increases in friction and peak film pressures with smaller percent reductions in friction torque as the supply pressure was reduced. Bearing friction torque was found to show a linear dependence on oil viscosity in the hydrodynamic regime where friction could be substantially reduced by using low viscosity oils. The effect of increased clearance was to reduce bearing friction and increase peak film pressures. The effects of reduced oil supply pressure on friction in crankshaft main bearings during cold-start warm-ups have been investigated. Friction reductions have been found to be most significant during cold running conditions at light loads. The thermal coupling between the bearing films and engine structure influences the film warm-up. Initially there is a rapid rise in film temperatures after which the warm-up is held back by the temperature of the surrounding metal. In addition to reducing bearing friction, reducing oil supply pressure also reduces the oil pumping work required; this represents an additional benefit which can be particularly significant under cold operating conditions.

The surface of diamond grinding tool manufactured by current production method exhibits stochastic nature in terms of different grit size, irregular geometry, random crystallinegraphic orientation, non-uniform spacing, and varying protrusion heights. These topography characteristics has been found having various negative effects for the abrasive performance, especially in high-precision applications, causing less controllable surface topography, inefficient chip flow, high working temperature and cutting force. The thesis covers the design and manufacture of laser generated novel abrasive pad with ordered abrasive grits from CVD polycrystalline diamond films, providing repeatable patterns and shapes for abrasive tool used in load controlled plane grinding process, which is regarded as engineered abrasive pad. Two major design parameters for engineered abrasive pad, including abrasive grit geometry and planar contact area between grits and workpiece surface, were investigated. An inverted test setup was developed to enable the evaluation for the performance of ordered abrasive pad under plane grinding operation. The analysis of material removal and surface topography was made and compared between conventional abrasive pad (randomly shaped grits) and two engineered abrasive pad (saw tooth and square frustum) to evaluate the influence of grit geometry on the grinding performance. Furthermore, a geometrical model was developed to simulate the surface roughness generated by engineered abrasive pad. Inverted tests were conducted allowing the validation of the model. Besides grit geometry, three abrasive pads (one conventional, two engineered) with different planar contact were also studied through inverted grinding test to evaluate the influence of planar contact area on grinding performance. An improvement of design for better material removal (31.5% in Chapter 7) was achieved by adjusting the planar contact area of engineered abrasive pad. It was found that laser generated abrasive pad can provide not the only superior surface finish, but also introduce less damage to the workpiece surface. More efficient chip flow and very little tool wear leading to a longer tool life was also observed. In particular, the engineered grits with symmetric shape (square frustum) exhibits superior performance over conventional grits (randomly shaped) and asymmetric grits (saw tooth). A good agreement between simulation and experimental results was found for surface roughness prediction, therefore provide good initial results for numerically studying engineered abrasives under planetary abrasive machining processes. Moreover, the evaluation of planar contact area also shows laser generated abrasives can provide significant advantages in material removal when designed with comparable planar contact area as conventional abrasive pad under specific applications, particularly when the abrasive contact geometry is designed to provide clearance in the cutting directions. Combining the findings above, a preliminary benchmark methodology was proposed for design of engineered abrasive pad, which enables the future optimization of engineered abrasive tool.

Energy use in buildings accounts for a large portion of global and regional energy demand and energy-related CO2 emissions. To steer the world towards a low carbon future, the development of new and more efficient technologies is required. In hot and humid climates, the high latent heat loads results in uncomfortable and unhealthy indoor environments, accounting for 30% to 50% of standard air conditioning energy requirements. Physical adsorption of water vapour on solid desiccants is found to offer an energy efficient alternative to conventional dehumidification process using standard air conditioning systems. However, the isosteric heat of adsorption released increases the surface vapour pressure of the solid desiccants resulting in a decreased adsorption capacity. In packed beds of solid desiccants, this heat of adsorption increases the bed temperature, exit air temperature and exit air humidity ratio subsequently imposing an increased cooling load requirement and high energy requirement in the regeneration of the solid desiccants. In literature, several approaches used in removing in situ the heat of adsorption released in packed bed systems were fraught with several limitations. To this end, an integrated packed bed-oscillating heat pipe (OHP) system was proposed. The concept was for the evaporator of the OHP to remove the heat of adsorption generated by the packed bed and reject at its condenser towards an energy efficient isothermal adsorption process. To achieve this, theoretical investigations of the individual systems and the integrated systems preceded experimental testing of a rig set up in the laboratory. For the theoretical studies, the OHP was helically coiled at both ends, filled with ethanol, methanol and water working fluids respectively at 50% volume fraction and numerically investigated using the Eulerian Volume of Fluid (VOF) model in ANSYS Fluent R15.0. The packed bed on the other hand was configured as a Heggs et al (1994) Z-type flow arrangement for enhanced radial flow using the Porous Media model in ANSYS Fluent R15.0 set up with the properties of Silica Gel. ANSYS Fluent R15.0 System Coupling limitations led to the development of mathematical models for the prediction of the integrated system performance. The experimental investigations were in line with the theoretical only in this case the optimum working fluid, deionized water, was used as the main working fluid in the helically coiled OHP (HCOHP). The results showed reasonable agreement between the performance of the numerical model and experimental prototype. The HCOHPs were capable of passively removing heat from the packed bed systems. Mean bed temperature reduction between the integrated packed bed-HCOHP system and corresponding individual packed bed configurations were about 5.61°C, 9.48°C and 10.14°C respectively for the large annulus (LAPB), medium annulus (MAPB) and small annulus (SAPB) packed bed configurations. Average packed bed outlet temperature reductions of about 6.61°C, 9.19°C and 6.29°C were also achieved for the respective configurations. A validation of the theoretical model showed average temperature difference of about 5.60°C between the experimental prototype of the integrated system and results predicted using experimental packed bed temperature data and HCOHP thermal resistance. Compared to other similar systems in literature, the integrated packed bed-HCOHP system showed capacity to passively remove significant amounts of the heat of adsorption released in silica gel packed beds towards isothermal adsorption.

The current design for a salient pole rotor consists of hundreds of laminations joined together to form a core pack, which is then pressed onto shaft. This thesis examines the possibility of using a solid cast rotor to reduce the complexity of rotor construction. To produce a solid salient pole rotor that has the capability to match the performance of the current lamination based rotor three fundamental areas which affect rotor performance were investigated. They are: • The magnetic performance of cast steel and a lower saturation Fe-Ni alloy for the magnetic shielding of pole faces. • The comparison of the performance of a solid steel rotor verses the lamination based rotor. • The use of laser cladding to produce a soft magnetic coating to prevent eddy currents from being induced into the rotor. Samples of cast steel were tested after various heat treatments were applied and their DC B-H curves were measured. The samples were examined, via optical microscopy, to determine the effect of heat treatments on their microstructure. The changes in their B-H curves and permeability were linked to the changes in microstructure by examination of the optical images. A prototype of a solid rotor was produced to determine its performance compared with the lamination based rotor. The prototype rotor was produced with a Fe-Ni alloy on the rotor pole faces. The prototype rotor was found to require an average of 72% more power in the field windings to match the performance of the lamination based rotor. This was true until the generator’s output reached 72kW when the Fe-Ni alloy on the rotor pole faces saturated, resulting in the air gap between the rotor and stator increasing from 2mm to 34.5mm. After the increase in air gap the prototype rotor required an average of 188% more power to match the lamination based rotor. The point at which the Fe-Ni alloy saturates is critical, as once saturated the power in the field windings must increase sharply to bridge the larger air gap. From this work it is clear that a cast steel with a better magnetic performance is required and that the point at which the lower saturation material on the pole shoes saturates needs to more closely match the normal operating power of the generator. Laser cladding was used to produce a coating that can be applied to the pole faces, with a sufficient thickness to allow a controllable increase in the air gap between the rotor and the stator at predetermined field strengths. The use of laser cladding in this way enables the pole face to act as a magnetic shield stopping heating in the rotor due to induced eddy currents. The use of annealing in both inert and reactive atmospheres was examined to determine their effect on the DC magnetic properties of the deposited coating. Annealing in an inert atmosphere of argon was found to improve the saturation magnetisation of the coating 30% better than annealing in a reactive hydrogen atmosphere.

The parametric studies investigated the cavitation phenomena occurring in Diesel Fuel Injection Equipment using immersed jets. The studies looked at cavitation from the incipient stage, to the fully developed stage, to leaving the fuel to cavitate for a sustained period of time. The studies were conducted with the aim of understanding the cavitation phenomena occurring inside the Fuel Injection Equipment making use of purposed built continuous flow rigs. The first part investigated the onset of cavitation taking place inside a mechanical 80 bar continuous recirculated flow rig that mimicked the flow inside the injectors spill valves as well as the flow inside the high-pressure pumps spill valves during the first stages of cavitation. High velocity jets of variable concentration were considered, from the incipient stage to the fully developed stage, focusing on the impact that changing the fuel composition has on the jets as well as on the impact it has on the geometrical parameters of the nozzle valves. The rig made use of custom made Acrylic, Brass and Aluminum-steel nozzles of Cylindrical, Hemispherical and Conical geometries respectively. The n-Octane, n-Decane, n-Dodecane, n-Tetradecane and n-Hexadecane mixtures were directed into an optically accessible receiver using single hole injector nozzles of 0.14mm and 0.25 mm hole diameters respectively. Parameters such as the fuel composition, the geometry and the material of the nozzles, as well as the operating conditions of the fuels were looked into where 25 repetitive sets of measurements were completed taking into consideration each parameter respectively. Incipient cavitation was associated with the flow outside of the nozzle and was visually observed at the top of the nozzle hole. Cavitation additionally occurred between the layers of the turbulent high immersed jet flow and the stagnant fluid inside the receiver. The onset of cavitation was obtained using the fuel Upstream Pressure to Downstream Pressure ratio. At the point of onset, the results showed that the Upstream Pressure to Downstream Pressure ratio decreased with the increase of n-Octane percentage in the mixture when considering the Cylindrical and the Hemispherical nozzles. When considering the Conical nozzle on the other hand, the critical Upstream Pressure to Downstream Pressure ratio increased with the increase of n-Octane concentration. The results also showed that the jet length and width increased when varying the diameter of the nozzle hole from 0.14 mm to 0.25 mm. Furthermore, the total Saturated Vapour Pressure increased with the increase in n-Octane concentration, where the increase in the propensity of the flowing fuel through the Cylindrical and Hemispherical nozzles, to cavitate was noted. On the other hand, the propensity of the Conical nozzles to cavitate decreased with the increase in Saturated Vapour Pressure. The second part of the study investigated the sustained hydrodynamic cavitation taking place inside a mechanical 1650 bar continuous recirculated flow rig, mimicking the flow inside the injectors spill valves and high-pressure pumps spill valves at a later stage of cavitation as the fuel was left to cavitate for a longer period of time, leading to the degradation of the fuel due to changes in the fuel’s chemical composition taking place during cavitation. A needleless 0.213 mm single hole diameter Cylindrical nozzle was considered, as the Commercial Diesel fuel, the biofuel Rape Methyl Ester and the Gas to Liquids paraffin blend were left consecutively to cavitate for a period of 30 hours. The volume flow rate was obtained as 1.129 Liter per minutes considering a Discharge Coefficient of 0.8. The results showed that by passing a 405nm laser over the 30 hours period through the cavitated fuel mixtures, a decrease with time of the transmission signal of the laser beam penetrating all tested fuels respectively was noticed. The laser beams experienced a decrease in strength due to the changes in the chemical composition of the fuel as high pressures and high temperatures took place inside the receiver. The effect of heating the fuels overnight inside a modified Water Bath tea urn at 60 degrees Celsius was looked into in order to separate the impact of temperature to the impact of cavitation alone. The effect of subjecting to fuel to cavitation and heating was greater than the effect of subjecting the fuel to heating alone. The Gas to Liquids fuel was visually transparent compared to the commercial Diesel fuel and had the highest laser transmission signal. Of all three fuels, the Commercial Aged Diesel fuel had the lowest laser transmission signal as the impurities inside the fuel changed the chemical composition of the fuel due to sustained hydrodynamic cavitation.

Porous air bearings enjoy some important advantages over conventional air bearing types such as increased load carrying capacity, higher stiffness and improved damping. However, these types of bearings have yet to find widespread acceptance due to problems with obtaining materials with consistent permeability, instability issues relating to the volume of gas trapped at the bearing surface in the pores, and manufacturing the bearing without altering the permeability. Using a series of fine grades of alumina powder to minimise surface pore volume it has been demonstrated that it is possible to consistently and reproducibly manufacture porous bearings by injection moulding and slip casting. The relationship between powder size, processing conditions, porosity, mechanical properties and fluid flow characteristics were experimentally determined. The temperature of processing and the green density were found to be the controlling parameters in the resulting fluid flow properties for a given powder size, Test bearings were produced from the range of processing conditions investigated. It was found that the fine powder size bearings were stable over the entire range of test conditions irrespective of their initial manufacturing route. The most important consideration for the bearing performance was the quality of manufacture. The bearings were found to be sensitive to the flatness of their working surface and quality of fit in their test holder. The bearings were compared with published theories for load capacity and stiffness. A reasonable agreement was found with load carrying capacity once a correction for surface roughness was incorporated. Stiffness predictions provided a useful tool for the analysis and prediction of properties such as optimum values of permeability for a given geometry, if certain allowances are made.

M.Ing. (Electrical & Electronic Engineering) / Switching losses in power electronic converters can be reduced by using snubbers, or resonant circuits. Simple snubbers can be implemented without much effort, but then energy is still dissipated, which reduces the efficiency of the converter. Regenerative snubbers are known, but these usually require complicated additional circuits. The use of nonlinear capacitors as turn-off snubbers has been investigated, and proved profitable. The main reason for this is the much smaller amount of energy which is stored in the the nonlinear capacitors, compared to linear capacitors. Resonant circuits reduce switching losses by allowing switchings to occur when the voltage across the switching device, or the current through the switching device is zero. This effect is called soft-switching and to obtain this, resonance between an inductor and capacitor is usually involved. Resonant circuits have the disadvantage that the installed switching power cannot be used optimally. This drawback has been reduced by using a saturable inductor in the resonant circuit. This thesis considers the use of both nonlinear capacitors and nonlinear inductors in a resonant phase arm. It was found that the nonlinear resonant elements lead to very low overdimensioning of the switching devices, and minimal switching losses in such a phase arm. Very few additional components are used, which keeps the cost of the converter down. A 1.5kW converter was constructed in which the double nonlinear resonant phase arm was implemented. This converter was investigated both experimentaly, and by means of computer simulations. The converter is also compared with the current state of the art. It is concluded that resonant phase arms with both. nonlinear inductors and nonlinear capacitors can function effectively in power electronic converters. Some important advantages are also assosiated with the use of the double nonlinear resonant circuit.