This study comprised five clinical trials in children and young adults, and a series of supporting laboratory investigations. The first trial compared a second generation glass polyalkenoate cement with amalgam as a restorative material in the deciduous dentition. The glass polyalkenoate material underwent a more rapid loss of anatomical form and marginal integrity, and also had a higher failure rate than amalgam. The second trial compared a minimal composite restoration/ fissure sealant technique with a conventional amalgam restoration as treatment for occlusal caries in permanent molars. Although there has been some loss of anatomical form and marginal integrity of the amalgam restorations, and loss of the fissure sealant component of the composite restorations, only 11 amalgam and 8 composites have failed. There was no statistical difference in terms of failure between the two techniques. The third trial involved a study of glass polyalkenoatecomposite resin class II sandwich restorations in premolar and molar teeth. Results showed that a layer of glass polyalkenoate cement brought out to the approximal tooth surface in the box areas was not a reliable method of restoration and certainly not a solution to cervical gap formation found with composite resins alone in the class II cavity. The fourth trial involved a study of a microfilled composite resin veneer technique for improving the aesthetics of anterior teeth. Results showed a low failure rate and high patient satisfaction over a 30 month period. The fifth trial involved the use of a hydrochloric acid—pumice abrasion technique for removal of superficial enamel stains. The technique was quick and easy to perform, and results were impressive. Patient satisfaction and appreciation was very high. Laboratory investigations were largely centred around the use of glass polyalkenoate cements in the sandwich technique. Results showed that etching of glass polyalkenoate cement with acid gave no advantages over a simple wash with water, prior to bonding to composite resin. Also that etching before the manufacturers recommended time, and failure to use an unfilled intermediate resin resulted in a poorer bond between glass polyalkenoate cement and composite resin.

Carbon fibre composites are increasingly being used in aircraft structures due to their superior physical and mechanical properties. The process of drilling of carbon fibre composites in aircraft manufacture is economically important since the extremely abrasive nature of the fibres limits drill life. The hole quality produced by drilling in terms of fibre pullout and matrix cracking affects the notch sensitivity of the hole. The present thesis describes an experimental and analytical study of drilling of the carbon fibre composites carried out with the support of British Aerospace (Military Aircraft Division). Full drill life testing was carried out using four low cost commercial cemented carbide drills, three of which had brazed inserts, and drill life was determined by measuring the outer drill corner wear. Hole quality was measured in terms of diametrical tolerance using accurate plug gauges. Drill forces were measured using a two component Kistler dynamometer and attempts were made to measure residual stress in the workpiece using the birefringent photoelastic technique. The hole quality was related to drill wear, cutting forces and heat generated during drilling. Independent tasks were carried out to relate cemented carbide physical and mechanical properties to wear using several standard sliding wear experiments. Three different cemented carbide tool materials were investigated in terms of cobalt layer thickness, carbide distribution and physical properties including hardness and fracture toughness. Independent sliding wear tests were performed using a Pin-on-Disc machine, lathe and machining centre. These tests allowed the materials to be ranked in terms of wear resistance when rubbing against carbon fibre composite. The fracture toughness was measured using the techniques developed by Palmqvist. The wear resistance was correlated to the physical and mechanical properties of the tool materials. Hole quality was studied experimentally using scanning electron microscopy and fibre pullout shown to be primarily dependent on the fibre-matrix interface bond strength and the intrinsic strength of the fibres. The surface morphology of the fractured fibres in areas of fibre pullout showed inultimode damage due to anisotropy of the carbon fibre composite and the dynamics of drilling. The degree and pattern of damage developed in the drilled holes was found to be highly directionally dependent. The experimental results and theoretical analysis showed that the degree of hole damage depends not only on drilling parameters but also on the material composition and the manufacturing process of the carbon fibre composite.

No description available.

No description available.

No description available.

Silicon carbide fibre reinforced alumina is a ceramic composite which was developed in conjunction with the Rolls-Royce Aerospace Group. The material is intended for use in the latest generation of jet engines, specifically for high temperature applications such as flame holders, combustor barrel segments and turbine blade tip seals. The material in question has properties which have been engineered by optimizing fibre volume fractions, weaves and fibre interface materials to meet the following main requirements : high thermal resistance, high thermal shock resistance and low density. Components intended for manufacture using this material will use the "direct metal oxidation" (DIMOX) method. This process involves manufacturing a near net shape component from the woven fibre matting, and infiltrating the matting with the alumina matrix material. Some of the components outlined require high tolerance features to be included in their design. The combustor barrel segments for example require slots to be formed within them for sealing purposes, the dimensions of these features preclude their formation using DIMOX, and therefore require a secondary process to be performed. Conventional machining techniques such as drilling, turning and milling cannot be used because of the brittle nature of the material. Electrodischarge machining (E.D.M.) cannot be used since the material is an insulator. Electrochemical machining (E.C.M.) cannot be used since the material is chemically inert. One machining method which could be used is ultrasonic machining (U.S.M.).The research programme investigated the feasibility of using ultrasonic machining as a manufacturing method for this new fibre reinforced composite. Two variations of ultrasonic machining were used : ultrasonic drilling and ultrasonic milling. Factors such as dimensional accuracy, surface roughness and delamination effects were examined. Previously performed ultrasonic machining experimental programmes were reviewed, as well as process models which have been developed. The process models were found to contain empirical constants which usually require specific material data for their calculation. Since a limited amount of the composite was available, and ultrasonic machining has many process variables, a Taguchi factorial experiment was conducted in order to ascertain the most relevant factors in machining. A full factorial experiment was then performed using the relevant factors. Techniques used in the research included both optical and scanning electron microscopy, surface roughness analysis, x-ray analysis and finite element stress analysis. A full set of machining data was obtained including relationships between the factors examined and both material removal rates, and surface roughness values. An attempt was made to explain these findings by examining established brittle fracture mechanisms. These established mechanisms did not seem to apply entirely to this material, an alternative method of material removal is therefore proposed. It is hoped that the data obtained from this research programme may contribute to the development of a more realistic mathematical model.

Confocal Raman microspectroscopy has been used to study the interdiffusion in polymer laminates at the interfacial region between the constituent polymer layers. The effects of the polymer molecular weight, annealing temperature, and annealing time have been studied. Three different laminates with various PMMA molecular weights have been examined, with a view to studying the hydrogen bonding interaction between the alcohol and ester groups of PVOH and PMMA layers. It has been found that v(C=O) band shows no apparent frequency shift due to hydrogen bonding. However, considerable broadening of the v(C=O) band has been observed at the interfacial region. In order to study the effect of annealing temperature, a PAN/PVOH laminate has been chosen. It has been shown that the degree of hydrogen bonding is reduced if the polymer laminate is annealed at a higher temperature than the glass transition temperature of both of the constituent polymers. No significant change has been observed after annealing the laminate for various lengths of time. It has been shown that Raman imaging and Raman microscopy can provide invaluable information about the molecular distribution and chemical interactions of various phases in polymer blends. The diffusion of pure water and also water from some ionic solutions into sulphonated polyetherethersulphone/polyethersulphone, SPEES/PES has been studied using Fourier transform infrared-attenuated total reflectance, FTIR-ATR spectroscopy. The effects of sulphonation level, annealing temperature, ionic concentration, and presence of some ionic species on diffusion of water into SPEES/PES has been examined. In addition the sorption and desorption processes, and diffusion into a laminate of SPEES/PES-PVOH has also been studied. It was found that the above diffusion processes are not Fickian nor Case II and is best described by a dual-mode sorption model. The diffusion coefficient for H2O in various cationic solutions into SPEES/PES has a descending order of Li[+] > Cs[+] > Na[+] > K[+]. Increasing the ionic concentration results in a decrease in the water diffusion coefficient. It was found that an increase in annealing temperature caused the diffusion curve to become more sigmoidal in shape with a decreases in diffusion coefficient.

No description available.

No description available.

No description available.