Industrial robotic manipulators can be found in most factories today. Their tasks are accomplished through actively moving, placing and assembling parts. This movement is facilitated by actuators that apply a torque in response to a command signal. The presence of friction and possibly backlash have instigated the development of sophisticated compensation and control methods in order to achieve the desired performance may that be accurate motion tracking, fast movement or in fact contact with the environment. This thesis presents a dual drive actuator design that is capable of physically linearising friction and hence eliminating the need for complex compensation algorithms. A number of mathematical models are derived that allow for the simulation of the actuator dynamics. The actuator may be constructed using geared dc motors, in which case the benefits of torque magnification is retained whilst the increased non-linear friction effects are also linearised. An additional benefit of the actuator is the high quality, low latency output position signal provided by the differencing of the two drive positions. Due to this and the linearised nature of friction, the actuator is well suited for low velocity, stop-start applications, micro-manipulation and even in hard-contact tasks. There are, however, disadvantages to its design. When idle, the device uses power whilst many other, single drive actuators do not. Also the complexity of the models mean that parameterisation is difficult. Management of start-up conditions still pose a challenge.

The following report investigates the use of abradable seal technology in industrial steam turbine applications. Abradable seals are a highly adaptable, widely applicable and cheap method of improving seal performance. By retrofitting abradable coatings to existing labyrinth seals, improvements in the range of 0.5% - 1% power output are seen with cost returns within two years [1]. The intention of this investigation was to develop fundamental understanding of the seal degradation process. A Multi Oxidation and Incursion Steam Test (MOIST) rig was designed from concept, through detailed design and finally commissioned. During commissioning the capabilities of the MOIST rig were defined. Although flowing steam operation was not achieved during this investigation, a theoretically proofed steam system is in place for future development. High temperature operation was achieved, although not reliably. Reliable, repeatable atmospheric tests were developed, representative of the start-up and shut-down operations of an industrial steam turbine. These tests produced relative velocities up to 121ms-1 between coatings and blades, and incursion rates up to 50μms-1. ST12T, Nimonic 80A and Nimonic 101 blade materials were tested against a bentonite-NiCrAl abradable coating. The results suggest that the bentonite-NiCrAl abradable coating tested was highly suitable as an abradable coating for all blade materials. Additionally, high temperature tests are necessary to fully prove the use of blade materials against coating systems. Simultaneously, non-MOIST rig oxidation testing was performed in the range of 580˚C - 800˚C in static air and 580˚C in flowing steam for exposure times up to 5000 hrs. Bentonite-NiCrAl top coat - NiAl bond coat and either a STG-9T or IN625 substrate were analysed to devise mechanistic models for the oxidation of the top coat, bond coat, substrate and all associated interfaces. It was concluded that steam oxidation is intrinsically different to air oxidation and that adapting the bond coat to include Cr would significantly improve the oxidation resistance and service life of the coating system investigated.

Bioresorbable polymers are used for a wide range of medical applications inside the human body including fixation screws and plates for broken bones, sutures and scaffolds for tissue regeneration. Over a period of months or years, these devices degrade by hydrolysis of the ester bonds; they become fully absorbed into the body, thus removing the need for repeat surgery. The degradation pathway of these devices, including the loss of mechanical properties, is of great importance. However, the complexity of the degradation process, and the number of factors involved, means that degradation trends are not fully understood. Also, for many of the commonly used biodegradable polymers, no theoretical understanding exists for changes to mechanical properties during degradation. The devices are therefore currently designed to be over-supportive, which may inhibit the healing process due to the stress shielding effect. A general mathematical framework has been developed through several PhD projects at Leicester to model the degradation of bioresorbable polymers. This PhD thesis consists of three parts. The first part reviews the existing understanding of bioresorbable polymer degradation. In the second part, the previous models are simplified and improved. These new models are then used to reveal an in-depth understanding of the underlying mechanisms of the degradation process. The third part of this thesis focuses on understanding the change in Young’s modulus of degrading polymers. In order to do so, a novel atomistic finite element method is developed, which can simulate the mechanical response of a representative unit of a biodegradable polymer. The method is used to study the mechanical behaviour of polymer chains once chain scissions are introduced. The study leads to a concept for effective cavities for polymer chain scission, called the Effective Cavity Theory, which can be used to predict the change in Young’s modulus of a degrading polymer.

The processing window is important for the semisolid processability of alloys. Applications of semi-solid metal (SSM) processing, especially aluminium alloys have been expanding for their excellent mechanical properties. However, the alloys well suited and commercially used for SSM processing today are limited in types. The main purpose of this Ph.D. project is to understand what makes an alloy suitable for SSM processing on both aspects of thermodynamics and kinetics. This research started with a fundamental study of binary alloys based on Al-Si, Al-Cu and Al-Mg systems (wt%): Al-1Si, Al-5Si, Al-12Si and Al-17Si; Al-1Cu, Al-2Cu and Al-5Cu; Al-0.5Mg, Al-3Mg and Al-5.5Mg. These are representative of Si, Cu and Mg contents in commercial alloys used for SSM processing. The Single-Pan Scanning Calorimeter (SPSC) and Differential Scanning Calorimeter (DSC) were used to investigate the liquid fraction changes during heating and cooling of these binary alloys. Thermo-Calc and DICTRA (DIffusion-Controlled TRAnsformations) software have been used to predict the fraction liquid versus temperature taking into account both thermodynamics and kinetics. Comparison of the predictions with experimental data revealed that the simulation results show the same pattern with experimental results in the fraction liquid-temperature relationship. However, the SPSC results are closer to the prediction than DSC curves are, even with the relatively large sample size associated with SPSC. This is potentially a significant result as predicting the liquid fraction versus temperature for the heating of a billet for semi-solid processing remains one of the challenges. The results also suggest that the fraction liquid sensitivity to time should be identified as a critical parameter of the process window for semi-solid processing in addition to the fraction liquid sensitivity to temperature. For microstructure investigation, microanalysis techniques, including Scanning Electron Microscopy (SEM) and micro-indentation testing, have been used on polished sections, and compared to theoretical predictions. In addition, some parts of this project are in cooperation with General Research Institute for Nonferrous Metals (GRINM), which aims to design and develop high performance semi-solid alloys. Thermodynamic analysis (both predictions and experiments) were carried out on thixoformed 319s (2.95Cu, 6.10Si, 0.37Mg, wt%) and 201 (4.80Cu, 0.7Ag, wt%) aluminium alloys. SEM techniques and Transmission Electron Microscopy (TEM) were used for the microstructural characterisation. The results showed that the DSC curves were sensitive to microsegregation in SSM alloys and resulted in a lower liquid fraction than the cast alloys calculated through the integration method from the DSC results. Al2Cu phase in SSM alloys 319s and 201 can be dissolved into matrix up to 0.4 % before melting temperature under 3K/min heating rate when compared with 10K/min heating rate. The DSC scan rate should be carefully selected as higher heating rate can inhibit dissolution of the intermetallic phases during heating leading to less accurate liquid fractions predictions.

Weld solidification cracking is an important issue in fusion welding. If undetected, the cracking defects can act as stress concentration sites which lead to premature failure via fatigue, as well as offer favourable sites for hydrogen assisted cracking and stress corrosion cracking. For welded steel products such as deep sea oil and gas transportation pipes, such defects heighten the risk of catastrophic in-service failures. Such failures can lead to devastating environmental, economic, and social damage. In this thesis, a comprehensive review of literature associated with steel linepipe and solidification cracking defects is first presented. Fluid flow prior to solidification is then observed and quantified in situ using a novel synchrotron X-ray radiography approach. The flow is dynamic at velocities up to 0.52 m/s and primarily driven via Marangoni flow. The relationship between the microstructure and mechanical properties of the welded linepipe are extensively characterised, with a new equation derived to assess fracture toughness based on the size and distribution of carbonitride precipitates. Weld residual stresses are measured both before and after linepipe expansion in the U-forming, O-forming and expansion process for the first time using a neutron diffraction technique. To further understand the fundamental mechanisms of solidification cracking during welding of high strength steels for subsea linepipe, a novel small-scale Varestraint test rig was developed for use in synchrotron X-ray imaging experiments and a Transvarestriant test rig utilised for industrial scale weldability tests. Solidification cracking during the welding of steel is observed in situ for the first time using a micro-radiography approach and the 3D crack network is rebuilt using a micro-tomography technique. It is proposed that solidification cracks nucleate from sub-surface cavities associated with: i) residual liquid high in solute and impurity concentration (hot cracks), ii) Ti (C,N) precipitated during solidification (that induce ductile microvoids). Solidification cracks then propagate via inter-dendritic hot tearing.

Nano-scratch testing has been used throughout this thesis in order to deepen the understanding of the processes occurring during the nano-scratch test, and to develop a method for calculating the nano-scratch hardness, from the quantifiable variables that are obtainable from the technique. Scratch testing on the macro scale is a well-established technique, however when reducing the scale of a mechanical test, whilst interest is focussed on the yield strength or hardness of the material, plasticity size effects must be explored. A literature survey concludes that size effects in nano-scratch testing have not been investigated in the past, thus this is the main subject of this thesis. In order to carry out this investigation a number of methods were trialled to calculate the nano-scratch hardness of pure, polycrystalline, oxygen free copper using both the edge forward and the face forward tip orientations of a diamond Berkovich indenter. The results obtained were compared to the indentation hardness and the most theoretically suitable method was adopted for later experiments carried out in this work; the technique for obtaining measurements was optimised, such that a genuine lateral size effect (LSE), whereby the nano-scratch hardness increases with decreasing scratch size, was observed. To further investigate the lateral size effect, nano-scratches were performed on a sample of single crystal copper in different work hardened states. It was observed that the nano-scratch hardness not only increases with decreasing scratch size, but also increases when the spacing between the dislocations in the material is reduced; when the level of work hardening in the sample increases, the density of dislocations increases, thus the spacing between these obstacles is reduced. In addition to this, the anisotropy of the nano-scratch hardness was investigated by altering the scratch direction in the (100) plane of the single crystal copper. It was found that the nano-scratch hardness is anisotropic and that the scratch hardness is largest when the scratch direction is parallel to the slip plane. It is known that the yield strength of a material increases with decreasing average grain size and therefore the effect of grain size on the nano-scratch hardness was considered. By reducing the grain size of pure, annealed, oxygen free copper, the nano-scratch hardness was observed to increase. In all experiments, the nano-scratch hardness values of scratches performed in the face forward tip orientation were larger than that of scratches performed in the edge forward tip orientation, when scratching the same sample condition. This suggests that scratch hardness is tip geometry dependent and in order to develop a method of calculating a tip orientation-independent scratch hardness, the shape of the indenter and the plastic flow of material around the indenter in that orientation, must be known and incorporated into the calculation, possibly as a drag coefficient. In addition to the geometry of the plastic flow, and therefore the plastic zone size, it was found that the nano-scratch hardness is also governed by the interaction between the geometry of the indenter and the grain boundaries in the material. Finally a number of experimental issues from the nano-scratch test are highlighted and researchers are encouraged to consider these precautions when using the nano-scratch test.

This thesis details research investigating issues with the way in which safety requirements (often termed assertions) are written for the specific application of high consequence arming systems. Existing methods for deriving such requirements focus on the approach through which these systems are designed. Currently this is based upon three main concepts: isolation, incompatibility and inoperability. These are often referred to as the 3I's, and are used in combination with a fourth I of independence. The issue motivating this research is that there is no rigour in the manner in which these are written and no methods exist to ensure completeness of the resultant requirements set. A systems engineering approach has been adopted to perform this research and considers the needs of stakeholders involved in specification of arming system safety requirements, from these requirements of the project are derived. A solution has been presented in the form of a set of 8 templates which allow repeatable specification of assertions, along with a set of 12 patterns which cover realistic and commonly used relationships between these templates. The template assertions are based upon a state machine format and adopt a novel view of the 3I's where attenuation, incompatibility, state changes and race are used to specify lower level and more detailed requirements than the existing methods. Application of the new approach to real industry projects showed that it identified assertions which were missed using the current state of the art methods. Through use of modelling it has also been demonstrated that the new approach produces a complete set of assertions which, when implemented correctly, provide protection against detonation in a given environment. This approach is intended for use alongside existing methods to produce a set of requirements which meet all regulatory needs, inclusive of independence, something which this approach does not consider.

Space charge, as one of the major concerns for the reliability of polymeric High Voltage Direct Current (HVDC) cables, has drawn wide attention in both academia and industry. Accordingly, measurement techniques along with accurate data interpretation have been required to study space charge behaviour in insulation materials and to provide solid bases for simulation activities. In this work, a high temperature space charge measurement system for mini-cables has been developed based on the Pulsed Electro-Acoustic (PEA) method. In parallel, simulation tools for space charge accumulation, based on non-linear unipolar charge transport models, the acoustic signal formation, transmission of acoustic waves, and their detection, have been developed for PEA measurement on mini-cables to provide an alternative way for interpreting the raw experimental data rather than the traditional approaches of reconstructing space charge information by signal processing and calibration. The simulation uses 2-D simulation tools and includes the clamping unit of the PEA cell to provide, for the first time, a detailed comparison of the two commonly used shapes, flat and curved, of the base electrode. Benefiting from the ability of applying isothermal experimental conditions of 20 – 70 °C, the transient of ‘intrinsic’ space charge accumulation due to the field and temperature dependent conductivity has been studied by means of a novel experimental data analysis method proposed in this work. In addition, the analysis provides a way to assess conductivity models by matching the simulation results with the experimental space charge results. By applying the simulation tools, the effect of the possible cable defects of non-concentricity and a mismatch between the insulation and semicon layers could be assessed. Furthermore, the origin of the bulk space charge signal experimentally observed in a mini-cable was found to be consistent with a radius dependent conductivity which may be a consequence of incomplete degassing.

Current and future space missions demand highly reliable, High Performance Embedded Computing (HPEC). The review of the literature has shown that no single solution could meet both issues efficiently at present addressing HPEC as well as reliability. Furthermore, there is no suitable method of assessing performance for such a scheme. In this thesis a novel cooperative task-oriented fault-tolerant distributed computing (FTDC) architecture is proposed, which caters for high performance and reliability in systems on board spacecraft. In a nut shell, the architecture comprises two types of nodes, a computing node and an input-output node, interfaced together through a high-speed network with bus topology. To detect faults in the nodes, a fault management scheme specifically designed to support the cooperative task-oriented distributed computing concept is proposed and employed, which is referred to as Adaptive Middleware for Fault-Tolerance (AMFT). AMFT is implemented as a separate hardware block and operates in parallel with the processing unit within the computing node. A set of metrics is designed and mathematical models of availability and reliability are developed, which are used to evaluate the proposed distributed computing architecture and fault management scheme. As a new development, extending the current state of the art, the proposed fault-tolerant distributed architecture has been subjected to a rigorous assessment through hardware implementation. Implementation approaches at two levels were adopted to provide a proof of concept: a board level and a Multiprocessor System-on-Chip (MPSoC) level. Both distributed computing system implementations were evaluated for functional validity and performance. To examine the FTDC architecture performance under a realistic space related distributed computing scenario a case-study application, representing a satellite Attitude and Orbit Control System (AOCS), was developed. The AOCS application was selected because it features a time critical task execution, in which system failure and reconfiguration time must be kept minimal. Based on the case-study application, it was demonstrated that the FTDC architecture is capable of fully meeting the desired requirements by timely migrating tasks to functional nodes and keeping rollback of task states minimal, which proves the advantages of the adopted cooperative distributed approach for use on board spacecraft.

The research presented in this thesis is concerned with lossless hyperspectral image compression of satellite imagery using the Integer Karhunen-Loève Transform (KLT). The Integer KLT is addressed because it shows superior performance in decorrelating the spectral component in hyperspectral images compared to other algorithms, such as, Discrete Cosine Transform (DCT), Discrete Wavelet Transform (DWT) as well as the Lossless Multispectral and Hyperspectral Image Compression algorithm proposed by the Consultative Committee for Space Data Systems (CCSDS-MHC). The aim of the research is to develop a reliable low complexity implementation of the computationally intensive Integer KLT, which is suitable for use on board remote sensing satellites. The performance of the algorithm in terms of compression ratio (CR) and execution time was investigated for different levels of clustering and tiling of hyperspectral images using airborne and spaceborne test datasets. It was established that the clustering technique could improve the CR, which is a completely new finding. To speed up the algorithm the Integer KLT was parallelised based on the clustering concept and was implemented using a multi-processor environment. The core part of the Integer KLT algorithm, i.e. the PLUS factorisation, has proven to be the most vulnerable part to single-bit errors that could cause a large loss to the encoded image. An error detection algorithm was proposed which was incorporated in the Integer KLT to overcome that. Based on extensive testing it was shown that it is capable of detecting errors with a sufficiently low error tolerance threshold of 1e-11 featuring a low execution time depending on the extent of clustering and tiling. A new fixed sampling method for the covariance matrix calculation was proposed, which could avoid variation in the data volume of the encoded image that would be beneficial for remote debugging. Analysis of the overhead information generated by the Integer KLT was carried out for the first time and a compaction method which is crucial to clustering and tiling was also suggested. The full range of the proposed enhanced Integer KLT schemes was implemented and evaluated on a desktop computer and two DSP platforms, OMAP-L137 EVM and TMDSEVM6678L EVM in terms of execution time and average power consumption. A new method for estimating the best clustering level, at which the compression ratio is maximised for each tiling level involved, was also proposed. The estimation method could achieve 87.1% accuracy in determining the best clustering level based on a test set of 62 different hyperspectral images. The best average compression ratio, recorded for Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) and Hyperion (spaceborne) images is 3.31 and 2.39, respectively. The fully optimised KLT system, achieving a maximum CR, could compress an AVIRIS image in 3.6 to 8.5 seconds, depending on the tiling level, while a Hyperion image - in less than 1 second on a desktop computer. On the multi-core DSP, an AVIRIS image could be compressed in 18.7 seconds to 1.3 minutes, depending on the tiling level, whereas a Hyperion image - in around 3.4 seconds. On the low power DSP platform OMAP-L137 the compression of an AVIRIS image takes 5.4 minutes and of a Hyperion image - 44 seconds to 2.1 minutes, depending on the tiling level.