Increasingly stringent emissions targets are encouraging vehicle manufacturers to prioritise reduction of vehicle mass. The falling cost of carbon fibre is increasing the viability of lightweight carbon-based body panel systems across a broad range of production volumes. In the present work an automated process has been developed for the manufacture of random fibre preforms at medium volume production levels (30-50,000ppa). This thesis seeks to understand the influence of key microstructural parameters on the mechanical and physical properties of carbon fibre laminates produced by directed fibre preforming. The principal parameters studied are fibre length, tow filament count and laminate thickness. A statistical process simulation has been developed to predict preform density variation and the results are compared with experimental tensile properties. Experimental studies have shown that there is a notable reduction in areal density variation and consequently an increase in tensile properties with shorter fibres (115mm to 6mm) and thicker laminates (1.5mm to 4mm for a constant volume fraction). Shorter lengths improved preform coverage and gave higher tensile strength, whilst thicker laminates reduced the presence of unreinforced areas which cause stress concentrations. Tow filamentisation has been induced by pneumatic means to reduce the mean filament count and maximise the mechanical performance when using inexpensive, 24K bundles. By maximising the level of filamentisation both stiffness and strength can be increased by 20% and 45% respectively. An analytical stiffness model is presented to predict the effect of tow filament count on the in-plane elastic constants. Filament count and out-of-plane fibre orientation distributions are determined from optical microscopy and are incorporated into a multi-level Mori-Tanaka based model. Predictions are within 8% of the experimental data for laminates containing large fibre bundles and 10% for laminates with highly filamentised bundles. An expression for critical bundle length has been developed for more accurate strength prediction, based on the number of filaments within the bundle. Experimental results confirm that the critical tow length is proportional to the tow filament count. Directed fibre preforming has been benchmarked against other competing processes in respect of mechanical properties, weight saving potential and cost. A full-scale demonstrator component has been manufactured using a variety of carbon composite solutions, which can all provide 40 to 50% weight saving for an equivalent bending stiffness to steel and greatly improved dent resistance. Directed fibre preforming has shown great promise for both semi-structural and structural components for medium volume applications, particularly when aligned fibres are introduced. The results from this work can be directly scaled for industrial application to provide a cost effective, lightweight alternative to steel.

The influence of the member orientation on the strength of joints formed with square hollow sections is examined. The bird beak joint system is a relatively new truss arrangement for square hollow sections, where the chord and the brace have each been rotated by 45° about their own centreline axes. Based on previous experimental testing it has been suggested that this joint system leads to a stronger joint arrangement. Finite element analysis has been used to study the strength and behaviour of such bird beak joints and to compare them to similar joints in CHS and the traditional RHS configuration to test this claim. A comprehensive study has been undertaken for bird beak X -joints and T -joints and comparisons are made with similar traditional joints in RHS and CHS as the parameters of the width ratio ß, the chord slenderness ratio 2y and the chord length ratio a are varied. Displaced shape and contoured stress plots are included to aid understanding of the failure mechanisms. The finite element work on K -joints allows comparisons of the strength and stiffness of bird beak K -joints with those formed in the traditional RHS configuration as the boundary conditions (at the ends of the members), the brace angle and loading conditions are varied. A limited amount of experimental work has been carried out in the laboratories at Nottingham University, with some assistance from the author, involving the physical testing of bird beak joints so that the finite element models can be validated. This work is reported and examined critically. The conclusions focus on the claims that the bird beak joints are stronger and how they differ from the traditional form of joints. Equations are presented to extend the design information available for a practical parameter range.

This work is concerned with the study of the mechanical behaviour of elastic laminated plates subjected to different boundary conditions. For the most part, each lamina is taken to be a fibre-reinforced material which contains a family of straight, continuously distributed fibres. When the modulus for extension in the fibre direction of each lamina is large compared with the other moduli, the laminate is termed 'highly anisotropic' and in such cases, approximate solutions can be obtained by treating the individual laminae as 'ideal' materials in the sense that they are inextensible in the fibre direction and also incompressible. In the context of the plane strain bending of a laminated cantilever, we show that the theory for ideal materials predicts the occurrence of singular fibres at the lateral surfaces of the laminate and at the interfaces between the individual laminae. In a highly anisotropic cantilever these fibres correspond to regions of high stress and accordingly a boundary layer theory is developed for these regions. The boundary layer solution, together with the ideal solution, provide a good approximation to the description of the response of the cantilever, but it is found to be inadequate near the intersections of edges and interfaces, and at corners. A separate investigation is made into the asymptotic behaviour of the stress in these regions. The major part of this thesis is concerned with the development of a general theory for laminated plates in stretching or bending. Given a laminate subject to specified boundary conditions, we define a single homogeneous equivalent plate which has material properties obtained. by an appropriate averaging of the material properties of each lamina. The equivalent plate is subjected to the same boundary conditions as the laminate and the equivalent displacements are determined by classical thin plate theory. The theory then assumes that the displacement components in each lamina can be expressed as the sum of the equivalent displacements and correction displacements. The correction solutions satisfy the conditions of displacement and traction continuity across the inter-laminar boundaries and the condition that the lateral surfaces of the plate are free from traction. In the special case of the laminae being isotropic, the solutions given by the theory exactly satisfy the full three-dimensional equations of linear elasticity. When the equivalent displacements are known, the complete solution in each lamina is readily determined and this is illustrated by examples. At the edges of the laminated plate, the prescribed boundary conditions are satisfied only in an average sense and therefore in these regions, an additional correction is required. The deviation of the calculated boundary condition from the specified boundary condition is used to determine the magnitude of this further correction.

The project examined the static and dynamic fracture mechanics of brittle materials. Destructive testing was performed on brittle, elastic, isotropic and homogeneous epoxy resin specimens made of Araldite CT-200 with Hardener HT-907. Three types of specimen were investigated, namely the three point bend (3PB) beam, the compact mixed-mode (CMM) specimen and the pressure tube. The 3PB and CMM specimens contained both narrow notches and real cracks. The pressure tubes included semi-circular notches. The real cracks were obtained by controlled fatiguing. The research involved the evaluation of the static mode-I and mode-II real and apparent critical stress intensity factors. The fracture surfaces and the phenomenon of crack branching were studied. The dynamic mode-I stress intensity factor was obtained at the inception of crack instability and also at branching. The concept of the existence of a unique relationship between the dynamic stress intensity factor and the instantaneous crack velocity was addressed. The possibility of modelling cracks in structural components by using cast shim notches in epoxy resin was discussed. The modelling of the static behaviour was proposed to be accurate and relatively easy. The dynamic behaviour would be approximately modelled; therefore suggestions on how to improve the dynamic modelling of propagating cracks were recommended, paying particular attention to the branching process and the instantaneous crack velocity. In addition to the experimental work, finite element analysis was conducted for the 3PB and CMM specimens containing narrow notches. It was shown that the specific geometry and loading conditions were unimportant and that the loading was conveniently characterised by the stress intensity factors for an equivalent crack. A method was devised which provided a relatively cheap and efficient means of determining stress concentration factors for what might appear to be complex geometries and loading conditions.

In this thesis a theoretical analysis is presented for statically loaded structural hollow section (SiuS) lattice girder joints having one compression bracing member and one tension bracing member welded to a rectangular hollow section chord member. A set of joint failure modes are established for gapped and overlapped bracings and the research is aimed towards establishing the yield and ultimate loads of such joints with the yield line method as the main analytical tool. The results of 150 joint tests, conducted both in isolation and in complete trusses at testing centres in three different countries, have been used to verify the theories proposed. A study of the parameters which are believed to influence the strength and behaviour of rectangular hollow section joints has also been made. Finally, a computer program has been written in Fortran to provide an automatic assessment of the strength of welded lattice girder joints having a rectangular hollow section chord member and either rectangular or circular bracing members.

An investigation of prestressed concrete containing steel fibres as secondary reinforcement to improve performance in shear, flexure and bond is reported. Emphasis is placed on the use of steel fibres in prestresssed extruded hollow core slabs, since these common precast elements have intrinsic difficulty in incorporating traditional secondary reinforcement due to their unique shape and manufacturing method. Two separate studies were carried out. The first study involved laboratory investigations into the bond between fibre reinforced concrete (FRC) and the prestressing strand, and the shear behaviour of laboratory-cast prestressed fibre reinforced concrete (PFRC) beams. The second part involved the factory production of fibre reinforced hollow core slabs in co-operation with a local manufacturer. The fibre reinforced hollow core slabs were subjected to conventional full-width shear tests, concentrated load shear tests, and to transverse flexure. For all laboratory cast elements, cubes, cylinders and prisms were cast to investigate compressive, tensile and flexural properties, respectively. Two types of steel fibre were investigated: hooked-end steel fibres at fibre volume fractions (Vf) of 0.5%, 1.0% and 1.5%; and amorphous metal fibres at Vf‘s of 0.28% and 0.56%. The trial production of fibre reinforced hollow core slabs necessitated the investigation of the effect of steel fibres on the extrusion manufacturing process. It was shown that fibre reinforced hollow core slabs could be adequately compacted with only slight increases in mixing water. Fibres were found to distribute randomly throughout the cross-section. However, the rotation of the augers affected the orientation of fibres, with fibres tending to align vertically in the web. It was shown that the addition of steel fibres to prestressed concrete has a negative effect on the bond between matrix and tendon, leading to longer transfer lengths. The effect of the increase in transfer length was to reduce cracking shear strengths by 4%. Shear tests showed that the incorporation of steel fibres could increase shear strength by as much as 45% for Vf = 1.5%. This increase in shear strength, known as the fibre contribution, was shown to be due to fibres bridging across the crack and an increased compressive resistance due to fibres arresting the propagation of cracks into the compressive zone. A semi-empirical equation for shear strength of PFRC elements is developed. It is given in two forms, one compatible with the present equations for prestressed concrete given in BS 8110 and Eurocode 2, and a second form compatible with that advocated for fibres in reinforced concrete. The equation makes use of equivalent flexural strength which is recognised as the most useful material property for design of FRC. The equation was found to give good correlation with the shear strength of single web beams cast both in the laboratory and under factory conditions. However, a overall strength reduction factor is required for full-width hollow core slabs to account for uneven load distribution and inconsistent web widths. This is consistent with tests on plain hollow core slabs found in the literature.

This work reports research concerning the properties of cermet coatings deposited by high velocity oxy-fuel spraying, which are designed to exhibit resistance to abrasive wear and high-temperature oxidation. Cermet powders have been produced by self-propagating high-temperature synthesis (SHS) reaction of elemental powder mixtures of Fe, Cr, Ti and C or B, to produce a cermet, containing an Fe(Cr) binder phase and a hard ceramic phase, TiC or TiB2. The Ti and C content in the powder mixtures were varied in order to evaluate the effect of the C: Ti ratio of TiC on the overall integrity of three different feedstock powders and coatings produced. Four cermet coatings were produced from these SHS powders, one TiB2-based and three TiC-based. Abrasive wear resistance of the coatings was evaluated using a dry sand rubber wheel (DSRW) abrasive wear testing machine, where the coatings were subjected to abrasion by both alumina and silica abrasives. The TiB2-based coating exhibited superior wear resistance when subjected to both alumina and silica. Of the TiC-based coatings, the equimolar coating exhibited superior resistance when subjected to alumina, and the excess Ti coating exhibited superior wear resistance when subjected to abrasion with silica. When compared with coatings produced from commercially available powders, namely, sintered and crushed WC-Co and blended NiCr-Cr3C2, the coatings produced from SHS powders exhibited comparable, and in some cases, better abrasive wear properties. Preliminary oxidation tests showed that all four coatings performed well at 500°C (the temperature at which WC-Co begins to degrade rapidly). They exhibited some oxidation at 700°C, and at 900°C, exhibited severe oxidation.

When a component is produced from textile reinforcement, it is well known that the reinforcement conforms to the shape of the tooling, predominantly by in-plane shear deformation. Current structural analysis techniques for composite components frequently neglect the effects of this deformation on subsequent mechanical properties. In this thesis the effects of shear deformation in the reinforcement on mechanical properties of the composite are shown to be significant, both for flat laminates with uniform reinforcement deformation, and for a component where deformation changes over the geometry. Methods are developed to predict the elastic behaviour and initial failure of components manufactured from textile reinforced composites, giving consideration to reinforcement deformation. One of the main objectives is to employ techniques which are purely predictive wherever possible, such that experimental test data are required principally for validation, rather than as input to the models. Implementation is performed in a modular fashion such that alternative models may be substituted at any stage in the procedure without affecting subsequent stages. Micromechanics models are employed to predict the properties of unidirectional composites from fibre and matrix properties and experimental validation is performed. A failure criterion is employed to determine lamina failure under biaxial loading. A simple model for woven fabric stiffness is implemented and extended to predict failure. Classical laminate theory is used to predict elastic and failure behaviour of angle-ply laminates; predictions are subsequently validated against experimental data. Material property and compaction models are incorporated into a draping simulation software tool which is used to create input files for structural analysis of components using layered shell finite elements, thought to be the most rigorous technique for textile composite components published to date. Results are shown to agree well with experimental data. To give full consideration of reinforcement geometry, initial studies of finite element modelling of the repeating unit cell are performed, whereupon the benefits and disadvantages of this technique are highlighted.

Freezing curve, NMR relaxation data, and steady field gradient and pulsed field gradient experiments were conducted on samples of water-logged woods excavated from the Tudor warship, the Mary Rose and on similar samples impregnated with Polyethylene-Glycol solutions: the polymer used as a bulking agent to prevent decay. At least two distinguishable populations of water molecules are found in wood. Freezing curves indicate the presence of approximately 0.38 g/g of hydration water, close to that observed in fresh timbers. Relaxation measurements on pre-treated samples provides evidence of a very tightly bound fraction, present at water contents of below 0.14 g/g 0i hydration water, with a second population of hydration water being present up to 0.1.8 9/9. Above this value a third ‘free' population is observed. The relaxation decays in longitudinal and transverse direction have been analysed in terms of a sum of exponentials. These indicate the presence of two populations of water which do not correspond to populations observed in freezing curve analysis. Exchange mechanisms dominate the temperature dependency of the relaxation behaviour in pre-treated samples, which is similar to that observed in other fibrous materials such as meat. However, t he different components do not appear to correspond to the physical characteristics of the wood and the spin populations cannot be associated with a distribution between identifiable compartments within the system. In PEG impregnated samples the contribution to the signal from the polymer is not resolvable on the equipment used. Samples treated with PEGs for which the degree of polymerisation is greater than 1540 show a dependency of relaxation characteristics on the water content of the sample. At low water contents PEGs of low molecular weight impart a mobility to the "bound" water molecules which is not seen in untreated samples. . Belt diffusion coefficients for water molecules in wood are anisotropic, and are reduced from those observed in distilled water. This reduction is brought about because water molecules are both held in a hydration layer, and bounded by the cellular structure of the wood. In impregnated samples the diffusion rates are lowered by a factor of 10, though this is not reflected in the relaxation behaviour. The anisotropy is reduced, and proton exchange mechanisms are blocked.

The use of composites for structural applications in the automotive industry has become more attractive due to the possible weight savings and part integration. Liquid moulding processes, where the reinforcement is prepared separately from the moulding operation, have been suggested as a suitable production method. However there are several obstacles to overcome before they can meet the high production volumes required. Whilst forming the preform, defects such as wrinkling and tearing can occur which can prevent successful moulding. This thesis addresses problems in the design and production of preforms. Current preform manufacturing processes and modelling techniques are reviewed. A model based on kinematic principles to predict fibre architectures for biaxial fabrics draped over arbitrary surfaces is described. A technique based on grid strain analysis was used to measure the deformation of various stitch bonded fabrics, and compared to the kinematic drape model results. The pure shear assumptions of the kinematic drape model assume the fabric has zero resistance to shear. Experimental measurements of fabric in-plane shear resistance were undertaken and compared for a range of fabrics. This highlighted some important criteria in fabric selection and possible problems in the kinematic modelling approach. The results from the in-plane shear tests were compared with those from the grid strain analysis to determine which fabric variables were important to fabric formability. Problems in the application of constraints within the kinematic model were discovered, and methods for overcoming them were suggested. Criteria which must be considered when selecting suitable fabrics for high drape preforms are discussed.