The so-called creep strength enhanced ferritic (CSEF) 9-12% Cr steels have been identified as the most promising class of materials for some of the key components in ultra-supercritical fossil-fired power plants, including the main steam pipes, headers and superheater tubings. These steels are less costly, and they have a lower coefficient of thermal expansion and a higher thermal conductivity when compared with austenitic stainless steels, making them less susceptible to degradation through thermal fatigue. However, experience has shown that the weldments in these steels are particularly prone to premature creep failure, due to a localised form of cracking in the heat-affected zone {HAZl, which is referred to as Type IV cracking. The work presented in this thesis is concerned with the effects of residual stresses and constraint on Type IV cracking. In the first part of this work, the residual stresses in a 25.4 mm thick, 324 mm diameter pipe girth weld, made in a P91 steel pipe, have been measured in both the as-welded and post weld heat treated (PWHT) conditions using neutron diffraction, and compared with the corresponding metallurgical zones across each weld. It was found that the highest as-welded tensile stresses resided near the outer boundary of the HAZ, and towards t he weld root region and these were not fully relieved by the applied PWHT. In both conditions substantial tensile direct and hydrostatic stresses existed across the HAZ, including the fine-grained and intercritically-annealed regions, where premature Type IV creep failures manifest in 9-12% Cr steel welds. Compressive stresses were found in the weld metal coinciding with the last weld bead to be deposited. In the second part of the work, creep tests were conducted at 625°C on cross-weld and simulated fine-grained HAZ specimens. The contributions of specific influences on creep performance (such as residual stress, constraint and creep damage associated with relaxation of residual stresses during PWHT) were then systematically examined. It was found that the geometric constraint (introducing a triaxial stress state) was beneficial in improving creep rupture life and that residual stresses (of the order of 50 MPa) showed a. clear reduction in life. Moreover there was some evidence that residual stress relaxation associated with PWHT may introduce some creep damage. The digital image correlation (DIC) technique was applied to resolve tensile and time dependent creep deformation properties along the length of P91 cross-weld samples. The results demonstrated the capability of the Die technique for full field measurement of strain during both room-temperature-tensile and high temperature creep tests in the vicinity of welded joints, where the gradients in microstructure and mechanical properties can be steep.

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Wetting and de-wetting processes play an important role in many natural and technological processes. In many cases, wetting is an essential prerequisite for application, for example in paint films, crop sprays, cosmetics, pharmaceutical tablets and in preparation of suspensions. Both equilibrium and dynamic processes of wetting are important in coatings. In many industrial and medical applications, some strategies to control drop-spreading on solid surfaces are being developed. One possibility is that a surfactant, a surface-active polymer, a polyelectrolyte or their mixture are added to a liquid (usually water). Recently discovered trisiloxane and other silicone-based surfactants show very unusual behaviour.

An investigation was made into the nature of permanent non-annealable mottle in the epoxy-resin system CT200/HT901 (C.I.B.A. Ltd.) as used for photoelastic analysis. Tensile and shear fracture specimens showed fibrilar formations, termed spicules attached to the fracture surface. Investigation of these spicules showed them to have been formed shortly prior to gel. They consisted of heavily cross-linked, fully cured resin having a higher ester content than the surrounding matrix. The spicules were more dense than the matrix, the difference being consistent with the strain necessary to produce 0.1 stress fringes; this irregular unannealable birefringence is termed mottle. Extraction of the insoluble fraction prior to gel showed fully cured spheres which could be the initiation points for spicular growth. The self-diffusion constant of the phthalic anhydride hardener was determined at various temperatures and cure times. Extent and rates of cure were determined using infra-red analysis and these were used to calculate the value of the self-diffusion constant necessary to sustain the spicule growth throughout cure. Comparison of the calculated and experimentally determined diffusion constants showed spicule growth to be possible for about two thirds of the gel-time. Density measurements at elevated temperatures enabled calculation of displacements in castings; differential displacements showed the post-gel stresses to be insufficient to cause microfracture. As spicule growth is apparently a diffusion controlled process, methods suggested for the elimination of spicules include the use of less diffusive hardeners of low exotherm coupled with low oven temperatures.

A thorough review of the literature has been undertaken on the prediction of the properties of composite materials from the properties of the components. This suggests that least progress has been made in the property area of toughness, and it is evident that the major techniques for the assessment of toughness are impact tests. A study of the influence of material parameters on the impact performance of fibre reinforced plastics is reported in this work. The material parameters studied were fibre type, diameter, geometry and volume fraction, and matrix properties. In order to study the failure process and energy absorption mechanisms in notched and unnotched specimens, both Charpy impact and slow rate tests were conducted using identical test geometries. Failure analysis depended to a large extent on optical and scanning electron microscope fracturegraphic observations of tested specimens. It was found that similar complex failures occurred at both test rates that could be analysed in terms of the standard strength and stiffness properties of the materials under test, provided that full consideration was given to the test geometry. Models have been developed to predict the critical conditions controlling the mode of failure, and it was possible to evaluate the influence of both test and material parameters. The energy absorbed was found to be dependent on the fibre failure conditons including modifications due to the specimen failure mode. These results suggested that the micro-mechanisms of energy absorption (eg debonding) were a secondary effect of straining the fibres to failure. The overall conclusion is that the Charpy test cannot be recommended for the comparison or characterisation of composite materials. Alternative techniques, based on the determination of the strain rate dependence of standard properties have been recommended together with preliminary supporting results.

The strength and failure characteristics of polyamide 6.6 filled with both glass and carbon fibres has been studied. It has been shown that provided there exists a moderately strong interface between the fibre and matrix, stiffness enhancement is as predicted by a modified rule of mixtures, but that strength is limited by an embrittlement of the material, which results in premature fracture at low strain. Failure mechanisms in a simple model composite were studied using optical microscopy and this suggested that matrix cracking initiated by the fibres was the principal cause of this premature fracture. Experiments in which fibre length distributions were determined both before and after fracture confirmed that failure sequences involving gross fibre fracture did not occur. This hypothesis has been confirmed by careful observation of the mechanical properties, together with optical and scanning microscopy and acoustic emission techniques, of the fibre filled thermoplastic. Limited experimental evidence suggests a more beneficial combination of properties might be obtained by using a mixture of glass and carbon fibres in the composite.

This thesis presents molecular dynamics simulations of nanoindentation and nanoscratching simulations on a number of oxide. materials. In particular, the oxides studied are used as thin films in optical coatings. These films provide a variety of different functionalities, including reducing infra-red transmission through the glass to lower the heating and cooling costs for buildings. Simulations are performed initially on magnesium oxide, which is studied as a test material due to the simple structure. Simulations are then performed on the rutile and anatase polymorphs of titanium dioxide, which are used in the anti-reflective and self-cleaning part of the coatings, respectively. Finally, simulations are performed into zinc oxide and a silver layer sandwiched between two zinc oxide layers. This multi-layered stack represents the typical structure of the energy saving part of the coatings. Mechanical properties of the thin films have been calculated and compared with experiment. Generally, there is a good level of agreement between the modelling and the experiments. Deformation mechanisms in the different systems have been identified so as to help understand the failure mechanisms in these coatings.

A comparative Life Cycle Assessment (LCA) was performed on two natural fibre thermal insulation products made from hemp and sheep wool and a benchmark mineral wool product. The assessment revealed both advantages and some disadvantages with the natural fibre materials. A major finding was the particularly low or absent impact in terms of global warming potential shown by the natural fibre materials. This was caused by the renewable carbon sequestered in the material withdrawing carbon dioxide from the atmosphere. With regard to the end of the product life, the study showed that only a proportion of the total amount of carbon dioxide was released in landfilling and composting scenarios. Dynamic vapour sorption analysis was conducted on varied natural fibres in order to develop a protocol for studying moisture sorption in natural fibres. Data from these studies were subsequently used in calculating the integral heat of wetting in hemp fibres. The energy release caused by the quantity of material studied in the LCA during predicted relative humidity fluctuations was found unlikely to affect the results of the LCA. However, where large quantities of natural fibres are used throughout a construction the heat of wetting may produce a notable difference in the internal temperature of a building and provide a degree of passive environmental control.

Synthetic sports surfaces have increased in popularity since their introduction into the United Kingdom in the early 1970's. In many sports, such as hockey and athletics, they have become the standard for play. The benefit of synthetic turf is commonly judged to be lower in maintenance requirements and operating costs, and having an increased quantity of play, when compared to natural turf. Synthetic turf has, historically, been perceived to be 'maintenance free' and there has been little or no research into the effect that maintenance has on its performance and physical characteristics. The aim of this thesis was to develop a fundamental understanding of the mechanical wear and decline in hydraulic performance of second generation synthetic turf surfaces, its impact on technical performance characteristics, and economic costs in relation to maintenance and usage.

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