To gain insight into the problem of impact on to composite materials this work has examined experimentally the characteristics of stress waves propagating through a multi layered plate due to a surface impact. Theoretical and numerical techniques have been developed for an impulsive line load acting on the upper surface of a four layer cross ply plate. These resolve the surface and inter lamina disturbances caused by the passing stress waves due to a normal line impulse onto a plate. The objective of this work was to examine the wave propagation in a cross ply plate with experimental techniques and compare the wave characteristics with the analytical predictions. To detect the passing of the stress waves on the surfaces and at the ply interfaces a piezo electric sensor was developed using polarized homopolymer of vinylidene fluoride (PVDF) film. The responses collected from surfaces and mid plane of the impacted plate were dominated by the low frequency contribution of the impact, so the high frequency shear wave responses were extracted with digital filters. The experimental results presented show that when the limiting wave velocity in the plate was that of a Rayleigh type surface wave the largest disturbance in the plate occurred on the upper surface of the plate, and that when the limiting wave velocity in the plate was that in an internal shear wave and the largest disturbance occurred at the mid plane of the plate. These results demonstrated that the presence or absence of shear waves could be resolved experimentally at the surfaces and ply interfaces of a multi layered material. A good correlation was seen between the experimental results and the analytical results which provided some verification for the analysis method.

This thesis contains a framework of medical decision support systems (DSS) and a case study of signal interpretation in electromyography (EMG). Methodologies required for architecture of such knowledge-based systems (KBS) are explored at both epistemological level and computational level in the thesis. Firstly, a research scheme is proposed under which system development is explicitly defined as a process of two stages, conceptual design and computational design. The conceptual design is mainly concerned with the medical domain. Its task is to abstract the problem-solving logic of that domain into symbolic forms of models. The computational design deals with more concrete issues related to system implementation and information technology (IT). Its task is to create applicable computing models in light of the conceptual system models. Object-oriented analysis (OOA) is introduced into the process of system analysis and design. At conceptual level, three fundamental inference patterns, forward reasoning (FR), backward reasoning (BR) and induction reasoning (IR), are abstracted as basic building blocks of domain problem-solving. Medical domain problem-solving can therefore be modelled as a hierarchical process made from the three basic patterns. A scheme extracted from a number of blackboard systems is determined as the framework's general problem-solving scenario. The blackboard scheme is then defined as a complex of interacting objects. At computational design, various computing algorithms are reviewed which range from object-oriented design (OOD), knowledge representation, uncertainty-handling to user-system interface. Decision strategies are also investigated in the context of EMG interpretation. The logic of medical decisions is revealed as a process of heuristic search and probabilistic thinking by Bayes' theorem. Decision-making is therefore modelled as a hierarchical process that combines inference reasoning and uncertainty-handling. An inference engine is designed using fuzzy logic and a decision network. It employs the decision principles of Bayes' theorem, but applies more realistic strategies of uncertainty-handling and inference. A preliminary EMG interpretation system is built under the framework. It is evaluated via a simulation study. The general methodology presented by the framework is shown to be a promising approach to system transparency, efficiency and performance.

Continuous advances in silicon processing technology have enabled devices to be more miniaturised and sophisticated. Most scientific Charge-Coupled Devices (CCDs), for example those used in astronomy, are following this trend; they are being scaled down and their doping profiles are becoming more complicated. Such trends increasingly require the use of three-dimensional (3-D) numerical simulations to provide improved designs. This thesis covers work focused on the three-dimensional simulation of buried-channel (BC) MOSFETs and CCDs. For BC MOSFETs a 1-D analytic model is developed to study their electrical characteristics and this is followed by 3-D numerical simulation work. Geometric-induced physical effects are thoroughly investigated using the 3-D simulation to optimise the scaling factor for the device. This simulation shows that 2-D simulation cannot estimate accurately the electrical characterisations of the narrow-channel and small geometry devices. For BC CCDs two X-ray astronomy CCDs are introduced: EPIC CCD as an open- electrode CCD imager and JET-X CCD. The optical properties of the EPIC CCD, used for ultra-low signal applications, were shown to be critically dependent on the dead layers and optical filter. It was clearly shown, for both devices, that 3-D simulations are useful for analysing charge storage and handling despite the complicated doping profile and sophisticated design structure. The charge handling capability of the JET-X CCD was found to be 9900 (electrons/?.m) using a 1-D analytical model. A 3-D static simulation of the JET-X CCD enabled estimations of the full-well capacity (60040 electrons), different depletion edge positions (< 5 % errors) and an optimised output gate voltage (between 3 and 4 V) for a higher charge transfer efficiency and demonstrated routes for optimisation and improvement. A 3-D transient simulation of the same device enabled estimations of the dynamic full- well capacity (61110 electrons), a dark current contribution (< 1 electron for a pixel clock cycle of 1.85 ?s) and a charge transfer inefficiency (< 0.001 % for a pixel clock cycle of 4.2 ns with a fall time of 0.4 ns). The 3-D simulation work suggests that a higher charge detection efficiency and charge transfer efficiency can be achieved with a higher-resistivity epi-material and a pixel clock cycle with a longer fall time (i.e. > 0.4 ns).

This thesis describes an experimental study of the compressive failure of T800/924C carbon fibre-epoxy laminates exposed in hot-wet environments. The specimens were immersed in boiling water so that the moisture equilibrium level was reached in a period of few weeks. The moisture level and moisture diffusion through the thickness of the laminate were measured experimentally and compared with theory (Fick's Law). Uniaxial compression tests were carried out in a Celanese test rig and the failure mechanisms were studied under various environmental conditions. Fracture characteristics were identified using optical and scanning electron microscopy. The critical failure mechanisms observed were in-plane and out-of- plane fibre microbuckling. At test temperatures higher than 50°C the failure mode switched from in-plane to out-of-plane microbuckling. As the temperature increased the shear strength and stiffness of the resin were considerably reduced. This decreased the amount of side support for the fibres and reduced the strain level at which fibre microbuclding occurred. Finally, recent theoretical models were employed to predict the compressive stress-strain response and strength of unidirectional laminates. It was found that although the theoretical models do not exactly predict the compressive strength of the laminate, they are sufficiently accurate for the cases examined.

For more than half a century turbulent mixing layers have been the subject of intense experimental and numerical investigation. With the discovery of primary, spanwise aligned and secondary, streamwise oriented vortices the interest in low and high Reynolds number mixing layers has been invigorated. The immense increase of computational capabilities in recent years has lead to an ever growing number of numerical simulations of mixing layers. However, numerical simulations have had great difficulties in reproductions the structure dynamics and entrainment mechanisms observed in the experiments. In this study Large Eddy Simulations of the low and high Reynolds number spatially developing, three-dimensional mixing layer are performed. At the heart of the presented studies lies the focus on the inlet conditions of the simulations. The effects of spatial and temporal correlation of the inlet conditions are studied for the low and high Reynolds number planemixing layer. It is shown that physically correlated inlet fluctuations lead to the development of the spatially stationary, streamwise oriented vortices observed in experiments. The effects of the presence of the streamwise vortices on the momentumand passive scalar fields are investigated in detail. In the latter parts of this work, the effects of varying the inlet fluctuation levels are reported. By altering the inlet fluctuation magnitudes the number and strength of the spatially stationary streamwise vortices can be controlled. The implications of this on the dynamics of the primary, spanwise aligned vortices are discussed. A change in the number and strength of the spatially stationary streamwise vortices is shown to be critical for the shape of the obtained probability density functions. If spatially stationary streamwise vortices are present, the obtained probability density functions are of the non-marching type. A lack of spatially stationary streamwise vortices produces marching probability density functions.

Super duplex stainless steel has a wide range of applications in chemical transport and processing facilities, especially in subsea oil and gas pipelines. A desirable combination of corrosion resistance and mechanical properties can be delivered by a balanced duplex microstructure. However, the microstructure of steel can be altered during processing, which can result in degradation of mechanical properties and corrosion resistance. In offshore environment, cathodic protection is widely used to improve corrosion resistance of gas and oil transportation pipelines. However, the application of cathodic protection can trigger the evolution of atomic hydrogen, which can adversely affect the macroscopic mechanical properties. Solute hydrogen induces premature failure, which is known as hydrogen embrittlement. In this project, microstructure evolution in super duplex stainless steel was first investigated. A new Cr2N precipitation mechanism has been proposed that a nano size lamellar M23C6 facilitates Cr2N rods precipitation in super duplex stainless steel. To study Cr2N precipitates in super duplex stainless steel weldment, transmission Kikuchi diffraction (TKD) was used to measure the geometrically necessary dislocation distribution (GND) around Cr2N. The TKD-GND results suggest a high GND density can be measured in nano-sized regions adjacent to Cr2N. The effect of hydrogen charging on dislocation multiplication in super duplex stainless steel was investigated and it is found that dislocation density multiplies by about one order of magnitude in steels with under 5% pre-strain, but dislocation density remains the same in steel with pre-strain at 10% and above. EBSD was used to study the effect of hydrogen on crack propagation. Hydrogen assists crack propagation through ferrite but can be trapped by both ferrite and austenite. It is found that austenite traps cracks by emitting dislocations or forming secondary grain boundaries ahead of crack tips, while in ferrite grains, the grain boundaries can impede crack propagation. The above findings provide new insight into microstructure evolution and hydrogen induced failure in super duplex stainless steel.

Ni-base superalloys are currently the most important material for high-temperature applications used in gas turbines. High amount of refractory elements used in the latest generations superalloys requires heat treatment for dissolution of inter-dendritic phases. However, occurrence of surface defects during heat treatment significantly reduced high-temperature performance of superalloys. To understand the mechanism of defect formation, a fundamental study on discontinuous precipitation and elemental sublimation is carried out. Discontinuous precipitation in single crystal superalloys during solution heat treatment has been examined. It is found that discontinuous precipitation is induced by local chemistry change near the casting surface and is dominated by the loss of Ni through sublimation. A phenomenological model is proposed to illustrate the phase evolution near the casting surface during solution heat treatment of single crystal alloys. Model Ni-Cr-Al model alloys were designed and made for measuring partial vapour pressure and thermodynamic activities of major elements Ni, Al and Cr in Ni-base alloys. Partial vapour pressures of Ni, Cr and Al in the γ phase were measured over the temperature range of 1473-1650K using Knudsen Effusion Mass Spectrometry. The partial vapour pressure of Al is about two orders of magnitude lower than that of Ni, and five times lower than that of Cr, suggesting that the sublimation of Al is almost negligible compared with those of Ni and Cr at solutioning temperatures. The kinetics of Cr sublimation was measured in long-term isothermal experiments at 1573K and it is found that Cr partial vapour pressure reduces significantly during the first 20 hours. Equations for calculating partial vapour pressure and thermodynamic activity at high-temperature range have been obtained. This fundamental study provides an enhanced understanding on microstructure instability of Ni-base alloys during heat treatment, and is useful for optimisation of heat treatment and alloy design of single crystal alloys.

Powder compaction is used in a wide range of industrial applications ranging from powder metallurgy, food, pharmaceuticals, consumer goods, catalysts, fuels briquettes, etc. Powder compaction can be defined in terms of 1) compactibility, which represents the ability to form strong compacts, which is quantified by compact strength and 2) compressibility, which represents the ability of the powder mass to form dense compacts and is described by the constitutive law. The aim of this work is to establish relationships between particle properties, (including mechanical properties of particles and interactions between particles, which are included in the contact law), and bulk powder properties (including compactibility and compressibility). Excipients used in pharmaceutical tablet formulations, such as microcrystalline cellulose, calcium phosphate and mannitol (a sugar) and their mixtures were characterised. Compacts of different densities were manufactured and their compressive and tensile strength was measured. The break force of curved faced tablet made of these materials and mixtures was also measured under an extensive range of conditions. A predictive model was developed and validated to estimate the break force of curved faced tablets using diametrical and uniaxial compression tests only; this has a significant practical importance in the pharmaceutical industry. The mechanical properties of individual particles were characterised using nano-indentation. The data for pharmaceutical excipient were augmented with results for a model powder material consisting of spherical aluminium particles. The now classic micromechanical model of Fleck was used as a theoretical framework to relate particle properties and constitutive laws for compaction. A parameter describing the strength of contact between particles was estimated using the strength of compacts. The contact strength parameter was then related to adhesive contact laws between particles. This work represents the first complete framework for relating contact law (which includes the elastic and plastic properties that determine the deformation of particles in contact and the friction and adhesion between particles) to compact strength.

Sintering is the thermal process that uses powders to form a new dense product by increasing temperature but holding it under the melting point of the material in use. Modelling the sintering process is important for fundamental understanding the behaviour of the particles during the sintering process instead of through empirical experimental work. In the first part of this thesis, a simplified method is developed to model the solid state sintering process which depends on the coupling between grain boundary and surface diffusion. A curve fitting method was developed to create a new relationship that relates the chemical potential at the junction of the grain-boundary and free surface to the neck size and the ratio of grain-boundary diffusivity over surface diffusivity. This relationship enables the de-coupling between the two diffusional processes when modelling the sintering process. The sintering process can, therefore, be separately modelled from the surface diffusion process, which greatly simplified the model for problems involving many particles such as those in a discrete element model. The results of the curve fitting method were first compared with the analytical Coblenz equations to allow for the validation and proofing of the new method in terms of modelling the sintering process; thereafter, comparisons were made with the full finite difference model using two parameters, namely diffusion coefficient ratio and applied stress. The curve fitting model matched well with the full finite difference model for the two parameters. In the second part of this thesis, two stages were undertaken: firstly, the new method was used in a variational model to simulate the two copper particles, and was compared with a new curve fitting-finite difference method for two sintering ratios. The variational model results were in good agreement with the new curve fitting-finite difference method. Secondly, multiple particles of copper were used in a variational model to simulate selective laser sintering for 27 copper particles. Laser scan speed, laser power, and particle temperature were collected from the COMSOL model, after which the particle temperature was used in the variational model to calculate the neck growth and shrinkage ratios between particles for different particle sizes. In the third part of this thesis, a molecular dynamics simulation code, LAMMPS, was used to investigate and understand the behaviour of nano-copper in the sintering process. Firstly, the melting temperature of nano-copper for different nanoparticle sizes was calculated and compared to four analytical models, after which neck size and shrinkage ratios were determined and compared with different diffusion mechanisms. The melting temperature numerical results matched well with the analytical nano-copper model. The hollow nano-copper improved the sintering process compared to solid nano-copper. Nanoparticle sintering has different behaviours comparing to micro-particle sintering. The nanoparticle sintering process is faster than for microparticle sintering; moreover, the melting temperature of the nanoparticles changed depending on size, when compared with microparticles where the melting point was constant.

This investigation is of mass, momentum and heat transfer applications of the idealised rotor-stator cavities using Computational Fluid Dynamics (CFD). This approach is based on previous literature that provides a fundamental view of the subject. However, this research is more focused on the development and simulation of high-fidelity computational models to refine the understanding of rotor-stator flow problems in engineering. An open source CFD toolbox, OpenFOAM, is used to solve Navier-Stokes equations and turbulence is modelled using Large eddy simulation (LES) approaches. The rotor boundary layer roughness is modelled by the parametric force approach, which is an ideal method to represent real-world roughness. Different types of rough wall conditions are imposed on the rotor. The roughness of the rotor wall affected the mean velocity profiles and turbulence intensity at the rotor. Increasing the roughness height transmits these effects to the stator wall. The outer wall of the rotor-stator cavity provides a passage to transport the roughness induced disturbances to the stator side, which tends to an unsteady flow even at minor roughness levels. The nanofluid heat transfer in the rotor-stator cavities is investigated using single-phase and two-phase transport models. Both models result in enhanced heat transfer rate by using different volume fractions of nanoparticles. The two-phase models provide additional information on the relative slip in the nanoparticle phase due to the Brownian and thermophoresis effects. Near the hot stator, particles are displaced away from the surface, which results in a mild reduction of heat transfer rates. The final section studies the Lagrangian particle dynamics and deposition in a Rotating Disk Chemical Vapour Deposition (RCVD) chamber. Here, the rotating effects of the disk highly agitate the particle phase, which enhances the deposition efficiencies on the rotor. Apart from that, carrier phase turbulence and thermophoretic forces are important factors in particle dynamics.