Aspects of the crystal structure of diamond, and its associated defects, have been considered with reference to the effect such characteristics might have on its mechanical properties. Also, established resolved shear stress models, which account for anisotropy in conventional Knoop indentation hardness of all single crystals, have been reviewed. Particular attention has been given to the role of microplasticity and the nature of crack formation in the deformed zone formed beneath the indenter. It is then shown that a similar approach can be applied to the case where a cone, made from a softer material, replaces the conventional rigid indenter. By using different materials covering a range of hardness, impressions can be formed beneath which there is a controlled density and depth of dislocations. In this work, the 'soft' indenter technique has been extended to high temperatures and applied to study the plasticity of various types of natural and synthetic diamond. Consequently, the effect of temperature on the critical resolved shear stress of synthetic type Ib, and natural type Ia and type IIa has been established. Above a critical threshold temperature for the onset of plasticity, time dependent growth of the impression volume occurs whilst the mean contact pressure is decreasing. It is shown that geometrical similarity, i.e. the ratio of the impression size to dislocated volume, is maintained whilst the critical mean pressure continues to be exceeded during this process of 'impression creep'. Activation energies of about 2.9 eV and 1.2 eV were determined, from rates of volume change, for natural (both type I and II) and synthetic type Ib respectively. Whilst no significant differences were observed between 98.9% 12C (natural abundance) and 99.9% 12C (isotopically enriched) synthetic diamonds, their behaviour was most like that of a type IIb diamond. Finally, by studying type la diamonds with a nitrogen concentration ranging from 14 - 750 ppm, evidence is obtained which supports the suggestion that this element reduces the intrinsic resistance to dislocation movement and encourages the initiation of cracks in the diamond structure.

Investigations concerning the microstructure and mechanical properties, composition and chemical bonding of alumina coatings have been performed. Alumina coatings have been deposited by both ionized reactive magnetron sputtering (IMS) and conventional reactive magnetron sputtering (CMS) in an argon/oxygen discharge onto stainless steel coated silicon substrates. X-ray diffraction (XRD) was used for the phase analysis, and nanoindentation was used to evaluate the mechanical properties. Substrate temperature during deposition was <500°C, which is the technologically interesting temperature range to coat temperature sensitive substrates such as tool steels. Formation of the x-phase was observed at 472°C. At substrate temperatures <472°C evidence for the formation of the amorphous alumina phase was found. Films containing a mixture of K and θ-alumina phases was grown at 430°C. The crystalline film hardness was 22+-1 GPa, which is equivalent to values reported for alumina films deposited by Chemical Vapor Deposition (CVD). Films grown at the same temperature by conventional magnetron sputtering were X-ray amorphous, and the hardness was found to be strong function of the substrate temperature. Furthermore, a novel, very high rate reactive magnetron sputtering deposition process for alumina hard coatings at substrate temperature ≤250°C has been developed. Utilizing pulsed D.C. power to sputter A1+A1Ox off the target surface and partial pressure control of the reactive gas to maintain a certain partial pressure value (accuracy of better than 0.005 mTorr), fully dense, transparent alumina coatings could be produced at 76% of the metal deposition rate. The coatings have an elastic modulus of,140 GPa, a hardness of 12 GPa, a chemical composition close to stoichiometric, and a refractive index of 1.65.

The increasing complexity of systems has made the design task extremely difficult without the help of an expert's knowledge. The major goal of this dissertation is to develop an intelligent software shell, termed the Knowledge-Based Design Support Environment (KBDSE), to facilitate multi-level system design and performance evaluation. KBDSE employs the technique, termed Knowledge Acquisition based on Representation (KAR), for acquiring design knowledge. With KAR, the acquired knowledge is automatically verified and transformed into a hierarchical, entity-based representation scheme, called the Frame and Rule Associated System Entity Structure (FRASES). To increase the efficiency of design reasoning, a Weight-Oriented FRASES Inference Engine (WOFIE) was developed. WOFIE supports different design methodologies (i.e., top-down, bottom-up, and hybrid) and derives all possible alternative design models parallelly. By appropriately setting up the priority of a specialization node, WOFIE is capable of emulating the design reasoning process conducted by a human expert. Design verification is accomplished by computer simulation. To facilitate performance analysis, experimental frames reflecting design objectives are automatically constructed. This automation allows the design model to be verified under various simulation circumstances without wasting labor in programming math-intensive models. Finally, the best design model is recommended by applying Multi-Criteria Decision Making (MCDM) methods on simulation results. Generally speaking, KBDSE offers designers of complex systems a mixed-level design and performance evaluation; knowledge-based design synthesis; lower cost and faster simulation; and multi-criteria design analysis. As with most expert systems, the goal of KBDSE is not to replace the human designers but to serve as an intelligent tool to increase design productivity.

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The use of water as a hydraulic fluid in a pump necessitates the use of conformal contacts to reduce the high rates of wear and leakage losses that result from the low viscosity and lubricity of water. Swashplate type axial piston pumps are ideal in this respect because they incorporate such conformal contacts. Furthermore, the development of such a pump for use with water, especially sea-water, critically relies on the correct selection and application of materials. The purpose of this research work is firstly to examine the contact conditions within an axial piston pump for a range of sleeved and lined components manufactured from a variety of different materials. The use of finite element analysis with gap elements is a useful way of determining the contact pressure distribution between conformally contacting components. It is shown that this method gives excellent agreement with available analytical methods for the two-dimensional cylindrical and axisymmetric spherical cases, and thus can be extended to layered components. Extension to three dimensions, when the contact cannot be accounted for by plane strain or plane stress conditions, is also possible, allowing a much more representative analysis of the contact conditions within an axial piston pump. No single combination of materials is identified as being the most suitable, rather, the method enables the consequences of choosing materials for their tribological characteristics to be examined. Once the contact conditions are known within the pump it is then possible to more accurately design the pump components. However, conventional deterministic methods are not appropriate for designing ceramic components, due to the inherent scatter of limiting defects, and statistical methods are necessary. Thus the second part of this research work is aimed at reviewing and examining the different probabilistic design methods with the long-term view of determining which, if any, are best suited to the design of ceramic components in this particular application. It is conduded that no single method adequately predicts the probability of failure of ceramic specimens with more complex stress distributions than four-point flexure bars.