The purpose of coating is to get a blend of unique properties at low cost which is not possible from other manufacturing processes. High velocity oxygen fuel (HVOF) is one of the most commonly used thermal spraying processes to produce wear and corrosion resistant coatings. Alongside wear and corrosion resistant properties the HVOF thermally sprayed coating process also induces microstructural heterogeneities which decreased the corrosion resistant properties. Considerable research has been reported on corrosion testing of the HVOF sprayed coatings by using electrochemical techniques. Some electrochemical techniques give area average results whilst other allows the effect of different features to be determined. The complementary use of basic electrochemical techniques with more advance techniques is missing in most of the previous research. In this research work potentiodynamic polarization testing, electrochemical impedance spectroscopy and scanning electrochemical microscopy were used to see if the combined results could provide a broader picture of corrosion processes taking place at HVOF coatings. Three HVOF coatings of different microstructural complexity i.e. γ-phase Inconel 625, γ + β-phase CoNiCrAlY and WC-CoCr cermet coating were tested. Potentiodynamic polarization results gave overall current response of the applied potential which included the current responsible for chemical reaction and current for charging and discharging of the double layer. The general corrosion ranking of different materials was established by measuring corrosion potential, corrosion current density and passive current density from polarization curves. The analysis of the polarization curves revealed that without careful consideration of experimental details significant errors can be introduced. Improved procedures for potentiodynamic polarization testing were demonstrated by deliberately altering experimental parameters. The localized corrosion due to chloride ions and Cr-depleted regions was also studied by potentiodynamic polarization testing. The correlation between individual microstructural features and their electrochemical response was established by EIS including equivalent circuit modelling. The impedance spectroscopy results also revealed the electrochemical changes due to immersion time and polarization. The electrochemical activity at high resolution was studied by more sophisticated spatially resolved SECM. The SECM imaging and heterogeneous electron transfer rate constant studies in feedback mode pin point the regions of different electrochemical activity. The SECM imaging and SECM feedback approach curves at stainless steel and bulk Inconel showed negative feedback all over the surface. The Inconel 625 coating showed both positive and negative feedback from the surface. The positive feedback regions correspond to less electrochemically active and negative feedback regions correspond to electrochemically active regions. The comparison between SECM images and microscopy images confirmed that the splat boundaries were the most active regions in the HVOF Inconel 625 coating. The heterogeneous ET kinetic study determined higher rate constant values at positive feedback regions and lower rate constant values at negative feedback regions.

This work addresses the characterisation of the micro-structure of fibre bundles in reinforcement textiles for composites and its influence on resin flow in liquid composite moulding (LCM) processes. Random variations in local filament spacing result in a non-uniform flow velocity field. Merging flow fronts due to differences in local flow velocities can lead to gas entrapment in the matrix phase. This results in formation of micro-scale defects, which can significantly reduce the matrix-dominated mechanical properties of the finished composite. An automated image analysis method was developed to precisely determine local filament distributions within complete fibre bundles. Based on two-dimensional micrographs, filament arrangements were characterised statistically by means of nearest neighbour distance and angle distributions. It was observed that the micro-structure becomes more uniform with increasing level of compaction. A micro-structure generator to reconstruct filament arrangements was adapted incorporating these measurement data. Transverse permeabilities derived from numerical simulations of steady-state flow on automatically discretised model domains were found to be log-normally distributed. With increasing model size, average values and widths of the distributions decrease, converging to the permeability of a complete fibre bundle. Similarly, average values and scatter decrease with increasing fibre volume fraction. The transverse permeability of random filament arrangements was found to be significantly smaller than for uniform filament arrangements. The void content in composite specimens produced by resin injection along and perpendicular to the fibre bundles was characterised with a developed image analysis process. Due to the more uniform micro-structure at increased bundle compaction, a decrease in void content was observed in the case of transverse resin injection. A first step towards void content prediction in a fibre bundle by numerical simulation of transient flow through a randomised filament arrangement was made. It was hypothesised that steady-state flow results may be used for the prediction of transient flow.

P92 steel is a high-alloy steel that has been specifically designed for operating at high temperatures (600°C - 650°C) and has found wide use in the power generation industry, particularly since 2005. For the successful installation and use of this advanced steel, all aspects of its behaviour, in terms of both metallurgy and in-service behaviour, must be investigated. Investigating all the relevant material aspects is beyond the scope of a single PhD, and so the Supergen consortium funds a number of projects working on different material aspects. The purpose of this thesis is to investigate, and seek a greater understanding of, the behaviour of welds in P92 steel so that their in-service behaviour may be better understood particularly the response of the material to post-weld heat treatments (PWHT), the optimum weld consumable composition and the microstructural development during creep-rupture. This understanding has been achieved through a combination of microstructural characterization, thermodynamic modelling and mechanical testing. Specifications for weld metals define a range of compositions; thermodynamic modelling has enabled a better understanding of how the composition affects the final microstructure of P92 weld metal (given that this work is based upon thermodynamic predictions, the understanding developed here is applicable to both parent and weld metal). Precipitation strengthening is important to the creep resistance of P92 and the modelling has revealed how precipitate levels vary based on composition. Using this knowledge, quality checks on P92 used by industry can better ensure the fitness for service of a material if an accurate composition is known; furthermore, this understanding will enable manufacturers to further tailor compositions to produce the strongest possible material. Following welding with P92 fillers, post-weld heat treatment is carried out, and there is a desire to perform this heat treatment close to the A1 temperature of the materials involved. As such, it is important to accurately know the A1 temperature of the materials being heat treated. A combination of thermodynamic modelling, experimental thermal analysis and microstructural characterization was used to investigate the key transformation of ferrite to austenite. This investigation focused on the effect of composition on the transformation temperature, A1, and the rate at which austenite could form during PWHT. An equation to predict the Ae1 temperature of P92 is produced and validated. The knowledge of how composition affects the A1 temperature is useful for both welds and parent material, enabling the design and selection of P92 material that will not undesirably transform during heat treatments. It is proposed that the equation for Ae1 allows the determination of maximum safe heat treatment temperatures and will reduce the likelihood of poor quality material entering service. Experimental work has demonstrated that during PWHT (or parent material tempering), equilibrium conditions are approached, confirming that Ae1 should be used to determine maximum heat treatment temperatures instead of the AC1 temperatures which are currently employed. Creep testing of three different weld consumables was carried out to determine which had the best properties for use in service, and to understand the microstructural features which controlled creep behaviour of these weld metals. Creep testing of weld metal has indentified that δ-ferrite causes early failure as the resulting precipitate-free zones (PFZs) are creep weak. The presence of localized δ-ferrite is caused by an inhomogeneous distribution of ferrite stabilizers, particularly tungsten within the weld metal, resulting in greater stability of δ-ferrite and its retention in the weld. Using this knowledge, alloy specifications of weld consumables and corresponding welding procedures can be improved to ensure a homogeneous distribution of elements so that localized weaknesses in a weld can be avoided. There is tentative evidence that tungsten plays an important role in the creep ductility of P92 and that variations in tungsten and silicon could lead to an optimization of creep strength. The outcomes of this thesis facilitate a better understanding of P92 parent metal and welds and provide results that are immediately applicable and useful to the power generation industry.

When an asphalt pavement is subjected to repeated traffic loads punctuated by rest periods, the acquisition of damage is interrupted by molecular relaxation and healing: the restoration of continuity across fractured interfaces. The healing effect is responsible for improved fatigue performance at high temperatures and dominates the laboratory-to-field shift factor in design. The mechanism of healing is not well understood, however. To describe this process, myriad investigations are collated with healing in high polymers, but neglect microstructural changes due to the damage processes that precipitate fracture. Yet, the remnants of deformation drive healing phenomena. An enhanced knowledge of healing and the effect of fracture could allow for the direct application of laboratory fatigue in pavement performance prediction. This thesis develops an understanding of the interrelation between binder structure and crack healing, using electron microscopy and mechanical analyses. Cryogenic microscopy indicates that the bulk is amorphous: phase separation in the form of bi-continuous or discrete structure is catalysed by surface effects including composition-dependent short-range interactions and thermal gradients. Environmental microscopy shows that the creation of a free surface during fracture perturbs the bulk solubility continuum, which stimulates phase separation in the form of interconnected fibrils. This system is sensitive to molecular scission and precludes healing by spatial interference and by reduced potential interaction. Rheological tests confirm the space-bound character of the microstructure and emphasise the requirement for an efficient method to quantify healing. Vialit pendulum tests validate the use of cohesive energy for this purpose and define the effect of fracture temperature: the capacity for healing is reduced by rupture of glassy fractions. Although susceptible to high variability, the outcome of direct tension testing confirms the involvement of crystallisable materials and the reduced proliferation of interfacial molecular interaction due to main-chain scission.

This thesis describes research examining the use of computational fluid dynamics (CFD) in structural wind engineering. It looks in particular at steady and unsteady RANS simulations and Detached Eddy Simulation and their use in the calculation of structural loads on static bluff building structures. Previous research across structural wind engineering and CFD is reviewed and critically examined with respect to structural engineering. CFD simulations are performed and compared with published flow data for simple cubes. Loading studies are performed for a complex building and the results compared with wind tunnel studies used in the structural design of the building. Some important local pressure and design forces are found to be highly dependent upon simulation parameters including the spatial discretisation used. In particular, local forces and pressures in the separation and reattachment regions cannot be consistently predicted. Standard industrial CFD methods for improving simulation accuracy including mesh refinement and increasing discretisation accuracy do not necessarily improve prediction of structural loads and explanations are given for this. Results for overall structural loads are found to be sufficiently settled and repeatable for comparison with experimental values, while some local forces and pressures cannot be predicted consistently. Recommendations are made for the appropriate use of CFD in structural engineering and for the future development of CFD techniques. In particular, improved representation of multiple turbulent scales in the free stream and separation regions is required.

This research addresses the development of a laser metal deposition process with wire feeding and melt pool temperature control. The system consists of a2 kW fibre laser, a CNC table, a wire feeder and a temperature monitoring and control system. A study of the influence of the main parameters on the process and on the deposited bead geometry was performed. The parameters analysed were: laser power, traverse speed and wire feed rate. As a result of this study, a process window was established for metal deposition of stainless steel 308LSi (wire) on stainless steel 304 (plate). The influence of the parameters on the bead geometry (height and width) was analysed applying the Design of Experiments methodology, using a full factorial design 3k. The results are presented, together with important practical considerations for laser metal deposition with wire. A closed-loop temperature control system was developed: it controls the melt pool temperature by means of modifying the laser power. The melt pool temperature was measured by a two-colour pyrometer, whereas a single-colour pyrometer was used for monitoring the workpiece (upper layer) temperature. A model of the melt pool was derived from a heat balance equation. It was then utilized for the design of the controller in the discrete domain, using the root locus method. The control algorithm was developed in LabVIEW software and executed in a computer. The control system was implemented successfully and was utilized to build single-bead walls and cylinders of stainless steel 308LSi. The study performed on the parameters and the developed temperature controller proved to be very effective tools to facilitate the transition to the deposition of titanium alloy Ti-6A1-4V, requiring only minimum adaptations. Single-bead walls and cylinders were also built in this material. Stable and smooth metal deposition was achieved for both materials. During the experiments, several strategies for the automation of wire metal deposition of multilayered structures were developed. Finally, mechanical tests were performed. The mechanical properties of the deposited materials are comparable to those in wrought (annealed) condition and to similar alloys made by laser powder deposition systems. The system developed in this work provides a means to perform stable and smooth wire metal deposition, achieving good mechanical properties. It also facilitates the transition to deposit different materials. It has a flexible structure and can be expanded or adapted to be used in other wire metal deposition systems.

In recent years, electromagnetic interference (EMI) has raised serious issues in terms of the unintentional radiation that disrupts the near proximity equipment from working properly. One solution to reduce the effects of EMI is the use of electromagnetic shielding. Carbon fibre composite (CFC) material is a promising customised product that has entered numerous industrial areas due to its attractive properties like high strength, low weight, and the resistance to chemical substances and corrosion. CFC has started to be used as electromagnetic shields, for example modern computer cases. However, not much is known about its electromagnetic behaviour. This research derives various models for CFC materials for the purpose of achieving better understanding to their interaction with electromagnetic waves at microwave frequencies. Throughout this research, the electrical properties of different materials have been investigated in terms of their shielding effectiveness (SE). The modelling was performed using the transmission-line modelling (TLM) method. The digital filter (DF) technique was used for small structures that are embedded in the system under modelling. In this way, the space mesh can be turned into coarser mesh. While maintaining the same accuracy, this technique has substantially saved on computational resources and has increased the speed of the modelling process. This in turn, has made it more feasible to model large scale practical systems. The formulae of DF cascading were derived to allow modelling systems of multiple embedded structures. Simulated models were validated by comparing them with the corresponding conventional fine mesh results. One-dimensional models were validated with the available analytic solution. Experimental measurements were conducted on panels made of this anisotropic material, which has manifested frequency-dependent characteristics that satisfy Drude model. These measurements have validated the corresponding numerical electromagnetic models. The final product of this study is gaining better knowledge about the electromagnetic behaviour of different materials. This knowledge can help in predicting the shielding performance when these materials are used within large-scale systems.

Optical Character Recognition (OCR) shows great potential for rapid data entry, but has limited success when applied to the Arabic language. Normal OCR problems are compounded by the right-to-left nature of Arabic and because the script is largely connected. This research investigates current approaches to the Arabic character recognition problem and innovates a new approach. The main work involves a Haar-Cascade Classifier (HCC) approach modified for the first time for Arabic character recognition. This technique eliminates the problematic steps in the pre-processing and recognition phases in additional to the character segmentation stage. A classifier was produced for each of the 61 Arabic glyphs that exist after the removal of diacritical marks. These 61 classifiers were trained and tested on an average of about 2,000 images each. A Multi-Modal Arabic Corpus (MMAC) has also been developed to support this work. MMAC makes innovative use of the new concept of connected segments of Arabic words (PAWs) with and without diacritics marks. These new tokens have significance for linguistic as well as OCR research and applications and have been applied here in the post-processing phase. A complete Arabic OCR application has been developed to manipulate the scanned images and extract a list of detected words. It consists of the HCC to extract glyphs, systems for parsing and correcting these glyphs and the MMAC to apply linguistic constrains. The HCC produces a recognition rate for Arabic glyphs of 87%. MMAC is based on 6 million words, is published on the web and has been applied and validated both in research and commercial use.

The excellent specific stiffness and strength of carbon fibre reinforced polymer composites means that the automotive sector has been investigating methods of implementing these materials into structurally demanding applications. The work detailed within this thesis supports ongoing research at the University of Nottingham into the automated manufacture of discontinuous carbon fibre reinforced polymer composite materials. Advances in the automation of composites manufacturing has meant that methods to effectively join these materials is required. This work provides a fundamental understanding of the differences that result from the adhesive bonding of a discontinuous fibre composite (DFC) compared to conventional fibre reinforced composite materials. The main objective of the project was to characterise the behaviour of adhesively bonded DFC adherends. Using a single lap shear joint geometry, an optimised fibre architecture and joint geometry was identified with a 2-part low temperature curing epoxy adhesive being characterised for industrial application. To further improve the performance of the DFC substrates, a fibre alignment technique was implemented that achieved properties comparable to those of more traditional non-crimp fabric composites. From the experimental investigations conducted, the use of discontinuous carbon fibre reinforced composites in bonded assemblies shows promise with the potential for use in structural applications.

This thesis is concerned with the propagation of elastic waves in polycrystalline materials. In particular, in establishing a relationship between the statistical properties of the wavefield and the statistical properties of the material via a correlation function. Here the study of elastic waves has been restricted to surface acoustic waves (SAWs), mainly because they are readily accessible using an optical scanning acoustic microscope (OSAM)