Rubber components under cyclic loading conditions often are considered to have failed as a result of the stiffness changing to an amount that makes the part no longer useful. This thesis considers three distinctive but related aspect of the fatigue failure exhibited by rubber components. The first considers the reduction in stiffness that can result from a phenomenon known as cyclic stress relaxation. The second considers fatigue crack growth encountered resulting in potentially catastrophic failure. The final issue relates to the complex topography of the resulting fatigue fracture surfaces. Previous work has shown that the amount of relaxation observed from cycle to cycle is significantly greater than that expected from static relaxation tests alone. In this thesis the reduction in the stress attained on the second and successive loading cycles as compared with the stress attained on the first cycle in a stress strain cyclic test of fixed strain amplitude has been measured for elastomer test pieces and engineering components. Adopting the approach of Davies et al. (1996) the peak force, under cyclic testing to a specific maximum displacement, plotted against the number of cycles on logarithmic scales produces a straight line graph, whose slope correlates to the rate of cyclic stress relaxation per decade. Plotting the rate of stress relaxation per decade against the maximum average strain energy density attained in the cycle reduces the data measured in different deformation modes for both simple test pieces and components to a single curve. This approach allows the cyclic stress relaxation in a real component under any deformation to be predicted from simple laboratory tests (Asare et al., 2009). Earlier work (Busfield et al., 2005) has shown that a fracture mechanics approach can predict fatigue failure in rubber or elastomer components using a finite element analysis technique that calculates the strain energy release rate for cracks introduced into bonded rubber components. This thesis extends this previous work to examine real fatigue measurements made at both room temperature and 70±1ºC in both tension and shear using cylindrical rubber to metal bonded components. Dynamic testing of these components generated fatigue failures not only in the bulk of the component but also at the rubber to metal bond interface. The fatigue crack growth characteristics were measured independently using a pure shear test piece. Using this independent crack growth data and an accurate estimate for the initial flaw size allowed 3 the fatigue life to be calculated. The fracture mechanics approach predicted the crack growth rates accurately at both room temperature and 70±1ºC (Asare et al., 2011). Fatigue crack growth often results in rough fatigue crack surfaces. The rough fatigue crack surface is, in part, thought to result from anisotropy being developed at the front of a crack tip. This anisotropy in strength whereby the material is less strong in the direction that the material is stretched might allow the fatigue crack to grow in an unanticipated direction. It might also allow the crack front to split. Therefore the final part of this thesis examines how, once split, the strain energy release rate associated with growth of each split fatigue crack develops as the cracks extend in a pure shear crack growth test specimen. The aim being to understand how the extent of out of plane crack growth that results might allow a better understanding of the generation of particular crack tip roughness profiles. Using a method of extending one split crack at a time, whilst keeping a second split crack at a constant length, it has been possible to evaluate the initial strain energy release rates of split cracks of different configurations in a pure shear specimen. It was observed that, for a split crack in a pure shear specimen, the initial strain energy release rate available for crack growth depends on the precise location of the split crack. It is also clear that the tearing energy is shared evenly when the crack tip is split into two paths of equal length, but as one crack accelerates ahead it quickly increases in tearing energy and leaves the slower crack behind. It is thought that this phenomenon is responsible for a lot of the roughness observed on the resulting fracture surfaces.

This research provides a comprehensive investigation into the effects of carbon nanotubes (CNTs) on the sintering behaviour, grain growth and properties of ceramics. Contradictory results reported in the literature on the effect of CNTs on sintering behaviour indicated the need for a systematic investigation under reproducible, controllable conditions. The sintering studies were performed using instrumented spark plasma sintering (SPS). It is a rapid sintering process that allows sintering to be studied in real time under isothermal conditions, enabling accurate calculation of time exponents and activation energies. A study into the effects of CNTs on the sintering behaviour of PSZ and B4C has shown that the presence of CNT content above the percolation threshold significantly reduces the sintering activation energies by 62 and 38% respectively. In both systems, the CNTS were also found to enhance the grain boundary diffusion mechanism of consolidation. Below the percolation threshold there was no significant effect on the activation energy. As well as the sintering behaviour, the grain growth of the PSZ and PSZ CNT composites was investigated. This research found that the CNTs acted as a grain growth inhibitor through a solute drag like mechanism both below and above the percolation threshold although with a high CNT content the solute drag effect was enhanced further with no significant change to the activation energy. The degradation of the CNTs was examined to determine whether they maintain their structural integrity during sintering. It was found that in both matrices with increasing temperature the CNTs were degraded to a greater extent. In the case of the PSZ-CNT composite the degradation was measured with respect to time at a series of temperatures to investigate the mechanism of degradation. Abstract ii The thermal properties of the ceramic CNT composites and porous ceramics were examined to determine the effect of CNTs on the transport properties of the matrix. It was found that the inclusion of CNTs in a PSZ matrix could enhance the thermal diffusivity and the residual porosity caused by burning them out causes a reduction.

Graphene is the first 2D material consisting of carbon atoms densely packed into planar structures. Graphene oxide (GO) is the intermediate derivative of chemically-produced graphene, which retains 2D basal plane structures but is also decorated with functional groups along the basal plane and edges. This functionality allows self-assembly of planar sheets into a paper-like material. However, formations of both intrinsic defects within the sheet structures as well as larger scale extrinsic defects in the paper are expected to significantly degrade mechanical performance. Strength provides the most direct evidence of defect related mechanical behaviour and is therefore targeted for understanding defect effects in GO paper. Such evaluations are crucial both from a technological perspective of realizing designed functions and from a fundamental interest in understanding structure-mechanics in 2D nanomaterials. A complete strategy of performing mechanical testing at different length scales is thus reported to provide a comprehensive description of GO strength. Both conventional larger scale mechanical testing as well as novel smaller length scale evaluations, using in situ atomic force microscopy (AFM) combined with scanning electron microscopy (SEM) and optical microscopy as well as structural probing using synchrotron FT-IR microspectroscopy, were applied to GO materials. Results showed that large structural defects determined mechanical properties of GO papers due to stress concentration effects whereas smaller scale intrinsic effects were defined by interfacial defects and stress concentrations within sheets. Synchrotron FT-IR microspectroscopy provided molecular deformation mechanisms in GO paper, which highlighted the interaction between in-plane C=C and cross-linking C=O bonds. A comprehensive description of macroscopic GO paper using evaluations of strength at the range of length scales studied was attempted, with a good correlation between predictions and experimental observations. This thesis therefore provides a hierarchical understanding of the defects impact on the strength of graphene-based materials from the macroscale to the nanoscale.

In Europe, the rapidly growing thermosetting foam insulation products industry comprises over 11,500 companies employing over a third of a million people and is worth about 6 billion Euros in trade. It is currently estimated 4-7 % of total new UK production is scrapped and goes to landfill. Estimated costs of disposing of this waste foam are of the order of £20 million/annum to the producers of foam panels and insulation blocks. A new strategic direction for rigid polymeric foams waste management has been developed converting the scrapped thermosetting foams into high added value material that can be used in various applications such as fire resistant insulating applications. Thus by this new innovative recycling process the waste is not only eliminated but benefits can be gained from the new material that comes out of it as a structural composite panel. The project involves a new concept that mixes fragmented scrap thermosetting foams materials with a proprietary liquid that cures at ambient temperature to form an incombustible material capable of withstanding high temperatures >1000 C. In this research different kind of polymeric foams used for manufacturing of reconstituted recycled samples. Sodium silicate solution has been chosen as the binder to binds shredded foams together. Due to fastening of sodium silicate curing different kind of acidic powders have been tested. For increasing of post properties after curing variety of fillers as an additive have been tried through out this research. Different foam cutting methods have been tested to find the suitable shredding routine. Rationale for selection of generic binder and its hardeners/fillers has been discussed in this project. Also as post properties evaluation compressive strength, thermal resistance, fire resistance and acoustic properties of recycled structural composite panels have been measured. At last a model for thermal conductivity of composite panels is developed.

The friction between a rubber surface in contact with a rigid surface is still not fully understood. Unlike other materials, friction behaviour in rubber is significantly dependent upon a variety of parameters due to its viscoelastic nature. The aim of this work is to understand frictional phenomena occurring on different length scales of intrest. In the first part of this work the influence of an entirely geometric factor on friction is confirmed by FEA and is validated by experiments for the first time. Under certain conditions, it can increase the frictional force significantly above that expected from a consideration of the interfacial coefficient of friction alone. This term is thought likely to make a considerable contribution to frictional sliding applications such as a tyre on a road surface. In the second part of this work an instability, observed at the rubber surface during sliding, is investigated. Despite experimental research in the past, virtually no information has been published on the modelling of the so-called Schallamach waves using FEA techniques. This work models successive Schallamach waves, giving the opportunity to investigate the transition of individual waves throughout the area of contact, for the first time. The use of FEA allows for a detailed stress and strain analysis at the interface and thus gives new insights into the onset of buckling instabilities. So far, Schallamach waves have only been observed experimentally for optically smooth rubber surfaces, however, during this work, surface waves have been also noticed for rough rubber surfaces. Furthermore, the examination of the frequency dependence of Schallamach waves allows for the consideration of a relationship to stick-slip behaviour. The third part of this work investigates the influence of the rubber surface topography as well as the rigid slider geometry on rubber friction under a wide range of experimental conditions. It was noted that subtle changes of surface finish significantly change the resulting frictional force. The knowledge gained from this can help in the design and understanding of more complex frictional interfaces.

This thesis examines the possibility of reinforcing thermoplastic matrices, notably polypropylene (PP) and polyhydroxyalkanoates (PHAs), by (a vegetable fibre) flax. An effort is made to enhance/optimise the mechanical properties of flax, PP composites through a micromechanical and macromechanical study. The fibrc'matrix interface is modified via chemical modifications as well as modifications in processing parameters (transcrystallinity). Effects of parameters like fibre length, fibre volume fraction and fibre-matrix interface modification on the mechanical properties of long flax fibre reinforced PP composites (compression moulded) as well as short flax fibre based composites (injection moulded) are studied. In order to get a better insight in the importance of these different parameters for the optimisation of composite performance, the experimental results are compared with model predictions using micromechanical models for random short-fibre-reinforced composites. For the injection moulded composites, different compounding routes are used and compared. The moisture resistance (pick-up and diffusivity) as well as dimensional stability (swelling) of natural fibre mat reinforced thermoplastics (NMTs), based on different kinds of flax fibres and PPs, are studied. The effects of a novel fibre upgrading method for flax fibres (DuralinTM) on the moisture pick-up and residual tensile properties of NMT composites are explored. Biodegradable composites based on flax fibre and PHAs are analysed. It is observed that addition of (cheap) flax fibre to polyhydroxybutyrate (PHB) could be advantageous as far as cost-performance of biopolymer composites is concerned. especially for stiffness critical applications. Mechanical properties of `biocomposites' manufactured through different routes (i. e. injection moulding and compression moulding) are compared. Addition of cheap flax fibres to an expensive and brittle PI IA composite leads to enhanced toughness of the composites. Abstract A life cycle assessment (LCA) study on glass-fibre-mat-reinforced-thermoplastic (GMT) and NMT manufactured by a current production method for thermoplastic prepregs followed by compression moulding into an automotive and non-automotive part is carried out.

An aspirating and dispensing printer established inside a robot gantry equipped with furnace and measurement table is used to prepare thick-film combinatorial libraries. Implementation of series of screening tests for ceramic inks that address stability against sedimentation, evaporation and particle segregation during drying, has provided a series of calibration inks can be used for calibration of this printer. The instrument can assemble ceramic mixtures with compositional accuracy of 1-3 wt %. By changing the amount of dispersant used in the inks or by printing onto a porous substrate, the geometry of residues from dried ceramic ink droplets can be modified to facilitate property measurements and uniform composition, as planned, can be achieved. The same material prepared in three ways, in the form of dried ink, ink-jet printed as for a combinatorial sample and by conventional compaction gave similar dielectric measurements. A combinatorial system has been developed so that combinatorial libraries can be printed, fired and screened automatically. A ternary A1203-TiO2-ZrO2 system was first studied using the developed combinatorial method. The particle segregation during drying of multi-component ceramic ink drops is not due to preferential sedimentation unless dispersant addition is restricted. The segregation is due to the partitioning of particles between the growing peripheral 'foot' that develops during drying and the diminishing liquid pool which contains vigorous recirculation flows. Better dispersed particles remain in the pool and hence are found in excess on the upper surface of residues. Less well dispersed particles join the 'foot' earlier in the drying process. The contact angle and height of droplets containing large amounts of dispersant, steadily reduced during drying until a minimum value was reached; the contact diameter being almost unchanged during drying. These droplet residues retained a dome shape. Droplets of suspensions containing small additions of dispersant terminated in a 'doughnut' shaped residue.

TiO2 is widely considered as a promising photocatalyst to degrade various organic pollutants in water, and to harvest sunlight renewable energy application. However, the efficiency of the photocatalytic reaction using TiO2 is not high due to its wide band-gap (3.22 eV, corresponding to the wavelength of 385 nm), which corresponds to the lower end of the wavelengths of solar light. The aim of this project is to use a continuous hydrothermal flow synthesis (CHFS) technique and other post-treatment methods to synthesize and tailor nano-TiO2 and TiO2-related photocatalysts for improved photoactivity. It was demonstrated that the rapid crystallising environment in a CHFS system resulted in the anatase phase of TiO2 (ca. 5 nm) with a high surface area and a high crystallinity. The CHFS system provides a flexible route of doping TiO2 at the atomic level (lattice doping) either to decrease the band-gap or to introduce intra-band gap states, which allow activation by visible-light. The structures of the resulting nanocatalysts were investigated using powder X-ray diffraction (XRD) and Raman spectroscopy. The quantity and chemical nature of the catalyst surface were determined by X-ray photoelectron spectroscopy (XPS). Morphologies of the products were characterized by Transmission Electron Spectroscopy (TEM) and Scanning Electron Spectroscopy (SEM). Band-gap energy was determined by UV-Vis spectrophotometry. A TiO2-CeO2 composite catalyst was successfully synthesized by CHFS. A stable solid-solution was indentified, which leads to a totally different optical property (i.e. with a narrow band-gap) when mixed with a methylene blue (MB) dye solution. All the composites materials show improved photodecolourisation rates. Novel 2D sodium titanate nano-sheets (ca. 400×500 nm) were developed with a high concentration of NaOH into the reactor. This material exhibits the highest photocatalytic efficiency amongst all materials being tested in this project. Several post-treatment methods were also adopted to further modify the CHFS-prepared nano-TiO2 samples. By heat-treating nano-TiO2 powder in air, the crystallinity of the sample was increased. By exposing the nano-TiO2 to ammonia atmosphere at a range of temperatures, products ranging from N-doped anatase TiO2 to phase-pure titanium nitride (TiN) were successfully obtained. N-doped TiO2 materials showed significant red-shift in band-gap. Surface modification of TiO2 in vanadium salt leads to a high surface absorbability and photo-oxidising power. Among all the modified samples, some of them indeed exhibited improved photocatalytic activity over the unmodified nano-TiO2. Moreover, the microwave dielectric properties of selected TiO2 samples (metal ion lattice doped) were also examined using sintered TiO2 discs. The results suggest that a useful dielectric resonator material can be achieved by introduction of certain dopants in combination with a spark plasma sintering (SPS) method.

The room temperature sol-gel processing technique was employed for the first time in the present work to fabricate the novel binary compound of the calcia-alumina (C12A7) system consisting of calcium oxide (CaO) and aluminium oxide (Al2O3) in a 12:7 ratio. The highest level of homogeneity and transparency of the C12A7 solution in ethanol was achieved by optimizing pH values, reaction dynamics and modified precursor structures. Studies were performed on this binary oxide in both thin film and powder forms. By using High Temperature X-Ray Diffraction (HTXRD) and Simultaneous Thermal Analyzer (STA), phase transformations in C12A7 powder were examined in situ under continuous heat treatment from room temperature to 1200°C. The samples were found to be amorphous at room temperature. As the temperature was increased, crystallisation was completed at 1100°C. The purity of C12A7 and the removal of redundant chemical by-products were confirmed by independent Fourier Transform InfraRed (FTIR) and Raman Spectroscopic measurements. C12A7 thin films were spin coated on single crystal MgO <100> substrates and the effect of heat treatment on crystallinity were investigated using XRD. Initial signs of the crystallisation of C12A7 thin film were observed at 800˚C and the complete crystallisation was achieved on heat treatment at 1100°C for 3 hours. Optical absorption spectroscopy measurements were made in the UV-Visible region and experimental data were analyzed to evaluate the dependence of the band structure of C12A7 crystalline phase on annealing temperature.

Offshore wind farm structures may have the potential to affect marine navigation and communication systems by reflecting radar signals. With ever increasing size of wind turbines it is necessary to better understand the influence of radar signals on wind turbine blades in order to minimise the radar reflecting potential. One possible way of reducing radar reflection is to use radar absorbing materials. In this thesis, epoxy composite materials reinforced with five different types of nano-size additives: carbon nanotubes (CNTs), carbon blacks (CBs), silver, tungsten carbide and titanium oxide are manufactured and tested to investigated their potential as wind turbine blade material that absorb radar signals. Nanoadditives/epoxy composites with additives content ranging from 0.05-1 wt. % were fabricated by a simple cast moulding process. The nanoadditives were dispersed in the epoxy resin by sonication method. The degree of nanoadditives dispersion was observed by examining the surface of the composite materials using scanning electron microscope (SEM). Complex permittivity of the nanoadditives/epoxy composites was studied using a free wave transmittance only method at a frequency range of 6.5-10.5 GHz. The effect of the percolation threshold of the direct current conductivity on the composite permittivity was analysed and discussion. In order to get a better insight in the importance of the results they were compared to existing models (Maxwell- Garnett, Bruggeman, Bottcher, Lichtenecker and Lichtenecker-Rother). A new model based rule of mixtures is developed to predict the complex permittivity of the composite. A model of wind turbine rotor blade made of the nanoadditives/epoxy composite was developed using Comsol-multiphysics software. The data obtained from the experimental work was inputted in to the model to generate result of backscattered energy verses composite permittivity as a function of nanoadditives content. A decrease in backscattered energy was noticed with increasing nanoadditives content. The results demonstrate that radar reflecting signals will be significantly reduced by incorporating nanoadditives in the composite materials.