The project investigates the feasibility of using sensor-based detection and processing systems to provide a reliable means of monitoring rolling contact fatigue (RCF) wear failures of silicon nitride in hybrid bearings. To fulfil this investigation, a decision was made early in the project to perform a series of hybrid rolling wear tests using a twin disc machine modified for use on hybrid bearing elements. The initial part of the thesis reviews the current understanding of the general wear mechanisms and RCF with a specific focus to determine the appropriate methods for their detection in hybrid bearings. The study focusses on vibration, electrostatic and acoustic emission (AE) techniques and reviews their associated sensing technologies currently deployed with a view of adapting them for use in hybrids. To provide a basis for the adaptation, an understanding of the current sensor data enhancement and feature extraction methods is presented based on a literature review. The second part describes the test equipment, its modifications and instrumentation required to capture and process the vibration, electrostatic and AE signals generated in hybrid elements. These were identified in an initial feasibility test performed on a standard twin disc machine. After a detailed description of the resulting equipment, the thesis describes the calibration tests aimed to provide base data for the development of the signal processing methods. The development of the signal processing techniques is described in detail for each of the sensor types. Time synchronous averaging (TSA) technique is used to identify the location of the signal sources along the surfaces of the specimens and the signals are enhanced by additional filtering techniques. The next part of the thesis describes the main hybrid rolling wear tests; it details the selection of the run parameters and the samples seeded with surface cracks to cover a variety of situations, the method of execution of each test run, and the techniques to analyse the results. The research establishes that two RCF fault types are produced in the silicon nitride rolling element reflecting essentially different mechanisms in their distinct and separate development; i) cracks, progressing into depth and denoted in this study as C-/Ring crack Complex (CRC) and ii) Flaking, progressing primarily on the surface by spalls. Additionally and not reported in the literature, an advanced stage of the CRC fault type composed of multiple and extensive c-cracks is interpreted as the result of in duced sliding in these runs. In general, having reached an advanced stage, both CRC and Flaking faults produce significant wear in the steel counterface through abrasion, plastic deformation or 3-body abrasion in at least three possible ways, all of which are described in details.

Identification of kissing defects in adhesive bonds has been reported to be an area of concern across a range of industries. To date the majority of work on this matter has focused on the development of advanced ultrasonic techniques. The current thesis focuses on the use of thermography, specifically pulsed and pulse phase thermography (PT and PPT), for the identification of kissing defects. Initially the thesis focuses on the application of PT and PPT for the identification of a range of defect types in a variety of materials to establish the effect of material properties on identification of defects. A numerical model has been developed to simulate the thermal evolution created during a PT or PPT experiment. After validation through a series of case studies, this model has then been used as a predictive tool to relate defect detectability to the thermal property contrast between defect and bulk materials. Where insufficient thermal property contrast exists defects have a limited effect on heat propagation through a component and therefore are not detected using PT or PPT. A means of producing realistic kissing defects in bonded joints is established. The addition of a small load to bonds containing kissing defects was found to open the defects sufficiently to enable their detection. Initial experiments use the application of a tensile load, via a test machine, to successfully investigate simulated kissing defects in single lap joints. A technique using vacuum loading on one adherend of an adhesive bond while PPT is carried out from the other adherend was successfully trialled. Vacuum loading enables the technique to be taken out of the laboratory. A low cost infrared detector, Flir Tau320, compared to the research based photon detector, Flir SC5000, was demonstrated to be suitable for application in PT, thus enabling a significantly lower cost tool to be developed.

Rim (or tip) driven thrusters with structurally integrated brushless PM motors are now an established technology with an increasing range of applications. In these thrusters, the stator of the motor is housed within the thruster duct, and the rotor forms a ring around the tips of the propeller. Such high pole number motors tend to be very thin radially, have very small axial length to diameter ratios, and have relatively large airgaps to accommodate corrosion protection layers on the surfaces of the rotor and stator. The relatively large diameter stator laminations of such machines tend, therefore, to have a very thin back of core and narrow teeth, which make them expensive and difficult to manufacture. This thesis proposes an alternative motor topology featuring a toothless stator whose laminations are manufactured from a single strip of steel that is edge wound into a spiral. The electromagnetic design of the motor was optimised for maximum efficiency for a given propeller torque and speed. The airgap flux density in was obtained from an analytical solution of Laplace and Poisson's equations of scalar magnetic potential. Electromagnetic torque was calculated for ideal square wave current distribution. Copper and core losses were estimated in the usual manner. Design of the machine was refined using transient finite element analysis, allowing for rotation of the rotor. The design optimisation revealed that there is an optimum radial thickness for the permanent magnet and number of poles at which the efficiency is maximum. A demonstrator machine was built and tested, and yield a 10% lower efficiency when compared with an existing slotted machine of the same diameter, with an increased volume in the slotless machine of 15%. A cost analysis yielded that the slotless edge-wound laminations are cheaper to manufacture than slotted laser-cut laminations, however the costs of the increased magnet material required are higher. This project has demonstrated a potential cost savings in the manufacture of laminations, however, for this specific thruster application the costs are offset by the need for more magnet material.

Scaffold design for bone regeneration is currently widely investigated as pore architecture can dramatically impact tissue formation in porous biomaterials used in regenerative medicine. A wide variety of 3D structures is used for this purpose, which has become even more important given the geometric freedom offered by emerging rapid prototyping techniques. Therefore, optimal design of pore architecture to maximize tissue formation and ingrowth is required. Tissue formation is frequently assessed in certain established scaffold structures, produced mainly as the end result of a particular fabrication process and its limitations. However, instead, scaffold architecture design should be based on the knowledge of how tissue actually forms in porous structures in the first place. Tissue formation within porous structures can be dependent on several parameters, such as cell generated forces, cell division, cytoskeleton and extracellular matrix arrangement. Tissue differentiation is also an important aspect as once cells commit to a lineage, the proliferation could decrease. These aspects have been extensively shown to be modulated biochemically. However, the impact of different 3D structures is still largely unclear. Therefore, in this thesis, it is aimed to characterise 3D tissue formation within different structures. For this purpose, an in vitro system with well-defined open pore slots of 1cm length, 1mm thickness and varying width (hundreds of micrometres) was used to characterise tissue growth solely as a function of pore geometry. This system provided a 3D environment for neo-tissue formation while minimizing nutrient limitations associated with full 3D constructs. This thesis is the outcome of three studies. The first was focused on tissue formation kinetics in four different pore widths of 200, 300, 400 and 500 μm. For this purpose, a unique system made of calcium phosphate cement with open pores was designed and fabricated. Several types of microscopy were used such as optical microscopy, time-lapse microscopy, epi-fluorescence microscopy and confocal microscopy. Results demonstrated that the material was biocompatible with Human Bone Marrow Stromal Cells and that tissue formation was strongly influenced by pore geometry. Both velocity of tissue invasion and area of tissue formed increased as pores became narrower. This was associated with distinct patterns of actin cytoskeleton organisation depending on pore width, indicating the role of active cell generated forces. The second study is a more detailed characterisation of the type of tissue regenerated and its organisation. The neo-tissue was seen to display an osteoid-like collagen matrix. The main elements constituting a tissue i.e. cells, actin cytoskeleton and collagen matrix were imaged and their organisation was quantified with various image analysis methods. Results showed a significantly higher alignment with the longitudinal pore axis in the 200 μm compared to the 500 μm pores for all the tissue components analysed. By relating tissue orientation with its expansion rate, the results suggested that increased tissue alignment could be an important factor enhancing tissue formation. In the third study, tissue differentiation was assessed as a function of pore size. Expression of intermediate and late bone markers was assessed, Alkaline Phosphatase and Osteopontin respectively. Results showed that both markers were expressed, indicating that the neo-tissue regenerated reached late state of differentiation and is prepared for mineralization. The expression of these markers was semi-quantitatively evaluated. ALP expression was expressed increasingly as tissue “age” increased. A gradient was observed with increasing staining intensity towards the starting point of tissue formation. Thus, the results revealed presence of distinct zones in which cells are in different states associated with various functions (proliferation or differentiation). Additionally, the expression of Osteopontin assessed semi quantitatively did not show any notable differences between pore widths. However, the results obtained displayed high variability between replicates. Therefore, it was only concluded that neo-tissue formed in both structures was able to express early (second study, chapter 4), intermediate and late osteogenic markers, although no significant differences were found between the different pore widths. This demonstrated that the tissue regenerated had committed to the osteogenic pathway, with the potential for full differentiation into mineralized tissue, which needs to be confirmed in future studies. Overall, the results presented in this thesis provide evidence for the hypothesis that pore geometry affects tissue growth capacity by modulating tissue organisation. Key factors governing tissue formation in vitro were elucidated, highlighting the importance of the interplay between cell division, cell mechanics, cytoskeleton dynamics, tissue spatial organisation, matrix deposition and differentiation in relation to porous structure.

Reverberation enhancement is a technology which allows the reverberation time of a room to be increased through the use of an electronic system. These systems have traditionally been applied to improve the acoustics of large concert halls but the technology can also be used in smaller spaces with several possible applications. Previous uses of reverberation enhancement in small rooms have largely consisted of direct transplants of systems designed for large concert halls. This work investigates the complications which arise when using reverberation enhancement in a small room due to the differences in the acoustic properties of the space and also the restriction on the channel count of the system due to physical constraints. The first part of this work deals with increasing the resultant reverberation time of the room without requiring additional system channels. This is achieved through the use of processing within the system. Two methods have been investigated. The first extends the resultant reverberation time without changing the feedback gain. The processing used for this purpose is either electronic reverberation or simple delay, both of which have been shown to allow significant increases in resultant reverberation time. These changes can be predicted accurately using diffuse field theory. The other method uses time-varying processing to increase the maximum stable feedback gain. This has been shown to allow increases in resultant reverberation time but also causes undesirable artefacts which limit the usability of this technique. The second part of this work focuses on the differences in the acoustic properties of small rooms and especially the ways in which these rooms differ from a diffuse field. This includes the consideration of the modal properties of the room at low frequency which are insignificant in a large room. It has been shown that the spatial and frequency variations of the room at low frequency can be reduced through numerical optimisation of the processing within the reverberation enhancement system. Finally, the diffusion of the sound field and the early energy in the impulse response have been considered. It is shown that restrictions on the resultant reverberation time may be required in order to create a subjectively acceptable acoustic response. Overall, this work has shown that by accounting for the properties of the room, excellent performance of the system can be achieved.

This thesis investigates the design and optimisation of constrained electromagnetic energy harvesters. It provides optimal design guidelines for constrained electromagnetic energy harvesters under harmonic and random vibrations. To find the characteristics of the vibration source, for instance vertical motion of a boat, the spectrum of the excitation amplitude should be obtained. Two Kalman filter based methods are proposed to overcome the difficulties of calculating displacement from measured acceleration. Analytical models describing the dynamics of linear and rotational electromagnetic energy harvesters are developed. These models are used to formulate a set of design rules for constrained linear and rotational energy harvesters subjected to a given sinusoidal excitation. For the sake of comparison and based on the electromechanical coupling coefficient of the systems, the maximum output power and the corresponding efficiency of linear and rotational harvesters are derived in a unified form. It is shown that under certain condition, rotational systems have greater capabilities in transferring energy to the load resistance and hence obtaining higher efficiency than linear systems. Also, the performance of a designed rotational harvester in response to broadband and band-limited random vibrations is evaluated and an optimum design process is presented for maximizing the output power under these conditions. It is furthermore shown that the profile of the spectral density of the measured acceleration signal of a typical boat can be approximated by a Cauchy distribution which is used to calculate the extracted power extracted by the proposed energy harvester in real conditions. In order to increase the operational bandwidth of rotational energy harvesters, subjected to time-varying frequency vibrations, a variable moment of inertia mechanism is proposed to adaptively tune the resonance frequency of harvester to match the excitation frequency. Also, the effects of combining the variable moment of inertia mechanism and adjusting the load resistance to increase the operational bandwidth of the system for constrained and unconstrained applications are studied. Finally, a ball screw based prototype is manufactured and the experimental results of its testing are presented which confirm the validity of the design and the derived dynamic equations of the system.

Polymeric coatings find applications in downhole water injector tubulars, protecting the inner surfaces from corrosion. Although these predominately epoxy-based coatings resist the harsh temperatures and pressures associated with a working injector, they are currently failing when exposed to mechanical damage. The mechanical damage takes the form of impact and wireline wear inflicted by the downhole 'tools' required in the maintenance of the injectors. In this work, experimental techniques have been developed for the successful direct observation of the impact and wireline wear damage mechanisms. The work has taken two concurrent paths, one investigating the abrasive wear range of supplied polymeric coatings utilising a pin-on-disc rig, the second studying the same coatings under impact conditions for which a specialised rig was designed and built. By comparing the recorded failure mechanism to physical properties of the coatings, relationships were found which led to recommendations initiating compositional changes to the coatings. One of the most significant findings of the work was that although the downhole coatings industry has spent many years developing and marketing thermoset based coatings, the under-utilised thermoplastic-based coatings appear to offer a 'better' solution to the problem. Unlike the modified epoxy coatings, it was shown that nylon-based coatings resist both wireline wear and impact damage without compromising the corrosion barrier properties of the coatings.

White structure flaking (WSF) as a premature wear failure mode in steel rolling element bearings is caused by white etching cracks (WECs) and perhaps butterflies formed in the ~1 mm zone beneath the contact surface under rolling contact fatigue (RCF). WECs are branching crack systems typically several millimetres in length that have a microstructural change called ‘white etching area’ (WEA) associated with the crack. Butterflies are smaller cracks initiating at material defects and impurities that form WEA wings that revolve around their initiators. Hydrogen diffusion into the bearing steel during service and transient operating conditions have been suggested as drivers of white etching features (butterflies, WEA and WECs). However the initiation and propagation mechanisms as well as the thresholds for WEC formation are not well understood. This is due to the difficulties of creating WECs repeatedly under laboratory conditions and the lack of a method established for mapping WECs in detail or 3 dimensions as typically only limited metallographic analyses are conducted over several cross-sections. A series of RCF tests have been conducted in this study to investigate the formation drivers and formation mechanisms of WECs using a two-roller RCF machine. WECs were successfully created in hydrogen charged 100Cr6 martensitic steel rollers under low-moderate concentrations of diffusible hydrogen (~1 ppm) and service realistic loading conditions (Pmax 1.5 – 2 GPa). However, only butterflies were formed under transient conditions with non-hydrogen charged rollers. One such butterfly was analysed in detail to further understanding of crack formation mechanisms and carbide dissolution as part of the WEA microstructural change. Based on the evidence obtained from the SEM, FIB tomography and STEM/TEM analysis, a void/cavity coalescence theory for initial butterfly crack formation and iron chromium carbide dissolution as part of the WEA formation mechanism is proposed. Metallography was extensively used in this project to view cross-sections of the wear zones subject to RCF. A metallographic serial sectioning technique was established to quantitatively map wear zones for the first time. Mapping WECs in their entirety and 3D modelling revealed the 3-dimensional morphology and orientation of WECs and maximised detection of possible WEC initiators. This study has for the first time quantitatively investigated the influence of diffusible hydrogen, load and rolling cycles on white etching feature formation and the thresholds of formation. The hydrogen charged tests showed that the formation of butterflies was independent of the concentration of diffusible hydrogen with the test parameters used, but dependent on contact pressure and number of rolling cycles up to a threshold. WEC formation thresholds were found at certain values of the concentration of diffusible hydrogen, contact pressure and number of rolling cycles. Extensive serial sectioning and 3D modelling of WECs also demonstrated that the orientation of WECs differed depending on the sectioning direction. It was found that the vast majority of WECs were contained in the subsurface wear zone and did not make any connection with the surface, thus dismissing surface initiation. The WECs often interacted with inclusions that were judged to be crack initiators and evidence was found that butterfly cracks could propagate to form WECs. The white etching features initiated predominately at short sulfide type inclusions, small globular manganese sulfide oxide inclusions and small globular oxide inclusions. Therefore strong evidence was observed for a subsurface initiation mechanism of WECs from non-metallic inclusions. A comparison of the WEC formations in the hydrogen charged two-roller tests was made with serial sectioning investigations of WEC formation in wind turbine gearbox bearings obtained from the field and those tested on a large-scale transient test rig (non-hydrogen charged). This was performed to understand if a difference in the WEC initiation and propagation mechanism occurs under the differing conditions. The comparison showed correlation between the WEC formation mechanisms as a high number of inclusions interacted with the WECs that were judged to be crack initiators and small/short sized inclusions predominated as the crack initiators. Therefore based on the serial sectioning analysis across various test specimens and bearings it is proposed that one mechanism of WEC formation is due to multiple linking of extended butterflies or small WECs in the subsurface to form larger WEC networks that eventually propagate to the surface resulting in WSF. The data also suggests that steel cleanliness standards analysing inclusion density (as opposed to maximum inclusion lengths) are more relevant in understanding butterfly/WEC initiation. However steel cleanliness standards used should record inclusions that are only a couple of micrometer’s in length/diameter.

Hydrostatic Pressure Machines (HPM), are a class of hydropower energy converter designed to operate at sites with heads below 3 meters; sites receiving increasing interest as the demand for power from renewable energy sources grows. The HPM is a ‘Pressure machine’, applying the pressure produced by differing water levels at a site, directly to the blades of the device to extract power. Prior to the current research, these machines had only existing as laboratory models. This thesis describes the design, construction and testing of a 5 kW prototype HPM installed at a re-activated mill site in Bavaria. Observations and performance test results from this full scale unit are then compared with the results of scale model tests carried out in the laboratory. New theory is developed to account for the geometry of the prototype machine and the variations in water levels encountered during operation. This is found to give very good agreement with performance measurements from both prototype and model tests, with no scale effects identified between the scales over the normal operating range of the machine. Several alternative rotor designs are tested at model scale, which demonstrate useful performance gains compared with the prototype machine. Direct blade force and cell pressure measurements are also obtained during model operation which has increased our understanding of the energy exchanges taking place between rotor and fluid within the machine. This in turn helps to identify the key machine geometries which impact performance.

Damage tolerant life assessment and the resulting component repair and replacement scheduling is crucial to the continued operation of UK power plant. Typically a major outage on a conventional power station takes 8 -12 weeks; there is a drive to minimise the scope of remedial works undertaken allowing the length of the outage to be reduced. Recent trends in life assessment methods are towards approaches that can be used to justify deferring invasive inspections and reducing the scope of the maintenance works. This thesis reports the development of a life assessment protocol for industrial steam turbine blade to disc interfaces which explicitly accounts for the residual stresses and strain hardening resulting from shot peening with a view to improving life cycle efficiency and reducing operator cost. A modelling approach has been developed which allows for the effect of shot peening to be explicitly accounted for in the damage tolerant life assessment process. The approach requires the input of experimentally determined residual stress, surface roughness and strain hardening profiles. Whilst the methods for determining residual stresses are well standardised, the optimum means of determining both the surface roughness characteristics (two and three dimensional) and the strain hardening profile (microhardness, X-ray diffraction and electron backscatter diffraction) were investigated as a first step towards standardising these measurements: It was found that a three dimensional analysis of the surface topography is most likely to capture the worst case defect. X-ray diffraction and electron backscatter diffraction measurements of cumulative plastic strain were shown to be most similar, with microhardness measurements appearing to overestimate the strain hardened region. Furthermore, the retained benefit of the shot peening process in terms of total life even under very high strain range LCF conditions has been clarified in terms of the applied stress distribution, specific material cyclic characteristics and residual stress relaxation. Under high strain range three point bend fatigue loading, the residual stresses and strain hardening in notched samples of the tempered martensitic steel under investigation did not change significantly. This allows the shot peening process to be specified for notched components under high strain range cyclic bend load, such as low pressure turbine disc blade interfaces, with an improved understanding of the resulting benefits.