Current and future structural applications for composite laminates frequently involve design solutions combining composite laminates and metal; the materials must be joined. Two conventional means of joining are available: mechanical joining and adhesive bonding. Both methods have critical disadvantages. A novel surface treatment for metals developed at TWI, Surfi-Sculpt™ leads to the formation of surface protrusions on metal surfaces. These protrusions are typically 1.0 mm high and 0.6 mm diameter. The surface modified metal can be bonded with composite laminates to form a Comeld™ joint. These joints can be described as a combination of mechanical fastening and adhesive bonding. There are many possible variables which could be applied to the metal surface. The variables include the shape, height, orientation and distribution (distribution pattern and density) of the protrusions. The aim of this work was to optimise the protrusions with respect to their geometry and distribution using the finite element modelling method for the Comeld™ joint under tensile loading with titanium alloy and cross-ply carbon prepreg composites. The simulations require multi-scale modelling techniques to transfer results between the global model, which is the reflection of the whole joint, and the unit cell models containing a protrusion. The two-dimensional simulations focused on the protrusion geometric parameters whereas the three-dimensional simulations focused on the protrusion spatial arrangement including the distribution pattern and density. Modelling of the entire joint geometry with two and three-dimensional global models was carried out using smeared properties for the adhesive layer which includes the protrusions. These models yield results for both quasi-static properties and stress distributions for these joints. Results from the simulations show critical effects on stress distributions arising from changing protrusion geometry. These joints show significant advantages over conventional joining technologies and their application would allow improved performance for combinations of metal and composite laminates.

A unique organic/inorganic nanocomposite of lead sulphide (PbS) quantum dots (QDs) embedded in substituted metal-free phthalocyanine (C6H2Pc) has been prepared by a simple and low-cost method. The preparation procedure consists of exposure of a thin spun film of non-peripherally octa-hexyl lead phthalocyanine to hydrogen sulphide atmosphere. The formation of the PbS QDs has been verified using X-ray diffraction and transmission electron microscopy techniques. From the transmission electron microscopic measurements, the average size of the PbS QDs is found to be 4.5 nm, which is smaller than the exciton Bohr radius. Independent Xray diffraction and optical absorption studies provide supportive evidence for the size of QDs. Quantum confinement gives rise to a clear blue shift in the absorption spectrum with respect to the bulk PbS. The QDs band gap has been estimated to be 1.95 eV from Tauc's law and the frontier energy levels of the PbS QDs has been derived. About two orders of magnitude increase in ohmic conductivity, from 6.0×10−12 for C6H2Pc to 3.1×10−10 for the nanocomposite, is observed by steady-state electrical measurements in sandwich structure between indium tin oxide and aluminium. Temperature-dependence of the electrical conduction is studied aimed to calculate the activation energy and determine the type of conductivity. The incorporation of the PbS QDs decreases the activation energy by about 0.5 eV at temperatures higher than 240 K. It is found that the Poole-Frenkel mechanism is in good consistency with the superlinear electrical behaviour of the nanocomposite. The frequency response of alternating current (AC) conduction is found to obey the universal power-law. The cryogenic study of AC conduction reveals that the correlated barrier hopping (CBH) model closely fits to the experimental data at temperatures below 240 K. The parameters obtained by fitting the CBH model point out that the hopping process cannot take place directly between neighbouring PbS QDs but involves the localised states within the matrix.

Globally, heart valve dysfunction constitutes a large portion of the cardiovascular disease load, causing high rates of mortality in European and industrialized countries. This is reflected in the database of the American Heart Association and the UK Valve Registry, showing a progressive increase in the number and age of patients in need of surgical interventions. Aortic valve (AV) dysfunction is significantly more prevalent than pathologies associated with other heart valves, accounting for approximately 43% of all patients having valvular disease. These statistics highlight the essential need for efficient and long term substitutes. However, the two types of replacement valves currently available in practice, i.e. mechanical and bioprosthetic valves, have only an estimated lifetime of around 10 years, after which the associated problems necessitate re-operation in at least 50-60% of the patients. Moreover, for patients under 35, the failure rate is nearly 100% within 5 years of the valve replacement surgery. The significant numbers of patients suffering from AV dysfunction, shortcomings to currently available valve substitutes, and the market demands for replacement valves has prompted increasing interest in the study of AV biomechanics. A fundamental study of the AV structure-function biomechanics is presented in this thesis. The mechanical behaviour of the AV is characterised at the tissue level, and the associated microstructural mechanisms established. In addition to the experiments, in depth mathematical models are developed and presented, to explain the observed experimental data and elucidate the micromechanics of the AV constituents and their contribution to the tissue behaviour. Tissue-level results indicate that the AV shows ‘shear-thinning’ behaviour, as well as anisotropic time-dependent characteristics. The microstructural experimental data indicates that there is no direct translation of tissue level mechanical stimuli to the ECM, implying that strain transfer is non-affine. Modelling micro-structural mechanics has confirmed that collagen fibres do not need to become fully straight before they contribute to load bearing, while the elastin network has been shown to contribute to load bearing even at high strains, further exacerbating the non-linear stress-strain relationship of the valve. The structural mechanisms underlying time-dependent behaviour of the tissue can be explained at the fibre level, stemming from fibre sliding and the dissipative effects arising due to fibre-fibre and fibre-matrix frictional interactions, suggesting a unified structural mechanism for both the stress-relaxation and creep phenomena. These outcomes contribute to an improved understanding of the physiological biomechanics of the native AV, and may therefore assist in optimising the design processes for substitute valves and selecting appropriate materials to effectively mimic the native valve function. Understanding AV micromechanics also helps quantify the mechanical environment perceived by the residing cells, which can have significant implications for cell-mediated tissue engineering strategies.

Microfluidic membranes are used in myriad applications, including use in microbioreactors. They serve as bio-catalyst surfaces or allow cell adhesion. However, creating such membranes requires complex manufacturing processes including multi-step self assemble. Recently, a nylon membrane was produced in situ in a flow channel [17]. This process is completed rapidly (within a few minutes), but such membranes are essentially only gas permeable. Control of the thickness and inclusion of porosity is important for effective membrane permeably for general solute transfer and could be sensitive for a given size range of molecules. In the present work, a simplified in situ fabrication technique has been used to produce a robust and novel protein micro-membrane. The proteins studied were BSA and fibrinogen with an acyl chloride to achieve protein crosslinking. Three acyl chloride crosslinkers were tested each crosslinker also generated unique surface morphologies and cross section morphological structures. Permeability of these membranes was tested by diffusion studies using dye molecules as well as the electrochemically active. A simplified approach of using ethanol to further modify the porosity of the membrane was established. Antibacterial membranes were achieved by exposing the protein membranes to copper sulphate solution. Tensile tests on the membranes showed that there was variation in membrane strength that was related to the crosslink or molecule type, and was also related to porosity.

In general, it is expected that concrete structures using Glass Fibre Reinforced Plastic (GFRP) rebars as reinforcement could have improved durability compared to normal steel reinforcement because of the corrosion resistance of the rebar. However, there are some aspects of the behaviour of the GFRP bars under high temperature that must be explored. The aims of this work are to predict the fire rating of the GFRP rebars when embedded in concrete elements by creating a model and to validate the model by full-scale experiments. The first part of this work evaluates the effects of alkaline environments on the rebar itself, the bond strength at interface between the concrete and the rebar, and the strength of the GFRP rebars at a range of different temperatures (20-120°C). The three types of GFRP rods investigated in this work were subjected to alkaline solutions at 60°C for three different exposure times i. e. 30 days, 120 days and 240 days. Tensile and flexural tests were carried out for the physico-mechanical characterisation on the treated GFRP rebars specimens. As the immersion period and temperature increased, the strength of the rebars decreased. Data obtained from the first part of the work were used to predict long-term performance of the GFRP rebar in fire. The effects of higher temperatures with time on GFRP reinforced concrete members were also studied experimentally in this work. As a result equations were developed. These were validated with the help of the fire tests carried out in second phase of this work on two full-scale GFRP reinforced concrete beams. The first beam was reinforced with GFRP made from thermoset resin and in the second GFRP made from thermoplastic resin was used. Shear reinforcement for the first beam were GFRP stirrups and for the second beam steel stirrups were used. Degradation of flexural and shear capacities due to fire was evaluated using the modified design codes which is based on assessment of the reduction in the initial strengths of concrete and GFRP reinforcement, resulting from the high temperatures developed inside the beam. A comparison of the results for each beam is presented. Fire resistance (load bearing capacity) of GFRP RC beams complied with British Standard BS 478. These results are published for the first time in this work. The predicted failure time using the model compares well with the fire test results. The 3 result also indicated that the basic fire model needed adjustment mainly due to a difference in the assumed and observed failure modes. The importance of data necessary for a more accurate model has been identified as a programme for future work.

A study has been made of the Instrumented Falling Weight Impact Test, investigating and analysing the effect of test parameters and specimen geometry on the characteristic results of the test. Two materials, poly(methylmethacrylate) and high density polyethylene are chosen, which exhibit typical extremes of brittle or ductile behaviour. High speed photography is used to monitor the development of deformation and progress of failure during the impact test. The major features of typical force-time curves obtained from the tests on PMMJL and HDPE are thus characterised in terms of failure development and quantified. Analyses are adopted which enable materials property data, such as modulus, E , fracture or yield stress, [Sigma][Subscript] f , [Sigma] [Subscript] y and a fracture parameter, G [Subscript] c to be obtained from the tests conducted on flat plates. A framework is proposed which would enable extraction of similar materials data from a wide range of plastics during routine testing with the falling weight test method.

A systematic investigation of the structural stability, evolution and hydrogenstorage properties of Mg-based hydrides was carried out, involving mechanical milling and chemical alloying. The effects of milling on particle size, lattice parameter, microstructure, and phase composition of the powder mixtures were characterised using SEM, X-Ray diffraction and quantitative Rietveld analyses. Mechanical milling was shown to be an effective method of refining the particle size, particularly when MgH2 is involved. The influences of the selected chemical elements, including transition metals, graphite carbon and rare-earth metals, on hydrogen desorption/absorption of various milled mixtures were clearly identified using coupled Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC). The as-received MgH2 shows an onset desorption temperature of 420°C. Mechanical milling reduces the onset temperature to 330°C. Chemical alloying, via surface catalysis and/or solid-solutioning, further increases the desorption kinetics and reduces the desorption temperature down to 250°C. The degree of such effect decreases from Ni, Al, Fe, Nb, Ti, to Cu. Further comparison of desorption characteristics of MgH2 mixed and mechanically alloyed with Ni clearly shows that the kinetic improvement and the effective reduction of the desorption temperature is mainly due to a catalytic effect, rather than solid-solutioning of Ni. Although posing little influence on desorption characteristics, graphite improves the absorption behaviour of MgH2. The rare earth metals, Y and Ce, do not seem to influence hydrogen desorption of MgH2 due to the formation of stable hydride phases, but CeO2 in the (MgH2+Ce) mixture provides a beneficial effect on desorption kinetics. Multi-component mixtures of (MgH2+15Fe+5Ce) and (MgH2+Al+Ni+Y+Ce) exhibit relatively fast desorption kinetics and the lowest desorption temperature at about 240°C and 220°C, respectively. Finally, mechanical alloying of the non-stoichiometric compositions of (3MgH2+Fe) and (4MgH2+Fe) effectively generated a new ternary hydride, Mg2FeH6, with a very high yield of about 80wt% from the (3MgH2+Fe) mixture, which is a promising candidate for heat-storage. The research findings laid a clear and valuable foundation for future development of new and cost-effective Mgbased hydrogen storage materials with a high capacity, a low desorption temperature and rapid kinetics.

A comprehensive study of domain switching process in different ferroelastic and ferroelastic/ferroelectric perovskite structured ceramics has been performed. The effects of thermal fluctuations on domain switching dynamics were investigated in the ferroelastic and in the ferroelectric case under static and dynamic electric and mechanical conditions. In the ferroelastic case, domain switching behaviour was investigated for different compositions, using different types of mechanical tests. Compression tests were carried out to characterize the ferroelastic properties, such as coercive stress, hysteresis loop and irreversible strain. Creep experiments were performed to study the domain switching time dependence at different stress levels. Domain switching kinetics during creep was characterized by implementing a rate model, based on thermal activation rate theory, which allowed the activation volume to be estimated. A Rayleigh-type analysis was performed to study the effects of stress amplitude, loading rate, temperature and composition on ferroelastic switching. Rayleigh-type relationships were proposed to fit the results and the rate model developed was applied to quantify the effect of the loading rate on the Rayleigh loops. Alternative methodologies were developed to assess the effects of rate and temperature on the coercive stress, providing original sets of data. A further application of the rate model provided an estimation of the activation parameters (volume and enthalpy). In PZT 5A at the coercive field the activation volume was calculated to be 2.44 nm3, with a reasonable consistency with the value obtained from creep tests (7.49 nm3). In the ferroelectric case, domain switching was studied by generating P-E and butterfly hysteresis loops and by analysing creep-relaxation curves. In creep experiments, the polarization and the strain were measured simultaneously, during the application of a constant electric field. An insight into the evolution of domain structure and on domain switching mechanisms was gained, highlighting analogies and differences with the ferroelastic case. Experiments at different frequencies, allowed the activation volume to be estimated at the coercive field (77 nm3). The relatively large value indicates small rate dependence and suggests a domain structure with broad and mobile domain walls, being the preferred sites for the nucleation.

This thesis investigates both experimentally and numerically the oxidation, sintering, melting and solidification processes of different nanoparticles under various thermodynamic scenarios, with a background for energy applications. Two sets of main techniques are adopted in this work, which are isoconvensional kinetic analysis and molecular dynamics simulation. Based on the techniques of simultaneous Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC), for first time the isoconvensional kinetic analysis is applied to study the oxidation of nickel and tin nanoparticles. This method is demonstrated capable of modelling one-step nanoscale oxidation and revealing underling kinetic mechanisms. Moreover, some distinct features of nanoparticle oxidation compared with their bulk counterparts are found such as melting depression, oxidation kinetic change in the vicinity of Curie point of nickel and pressure-related two-step oxidation of tin nanoparticles. The detailed study from Molecular Dynamics (MD) simulation establishes a three-stage sintering process of two nickel nanoparticles, which is unable to be described by bulk continuum-level models. MD is applied to study the interaction between nickel and aluminium and its consequent thermo-mechanical and structural property evolution in a nickel-coating aluminium particle in a heating and cooling cycle. The simulation successfully predicts the atomic diffusion during melting and the formation of glass and crystal phases, and allows for the estimation of interior core-shell pressure. Reactive MD is then applied to simulate the oxidation of silicon nanoparticles. It predicts well the exothermal reaction process and experimentally reveals the oxygen exchange process.

The degradation of polyurethane (PU) coil coatings were studied with step scan phase modulation photo-acoustic (SS-PM-PA) FTIR, confocal Raman mapping (CRM) and scanning electron microscopy (SEM). PU coatings were oven cured for 30 seconds to reach a peak metal temperature of 232°C. The cured coatings were exposed in a QUV A accelerated ageing test with exposure time intervals of 1200 hours and 4098 hours. Isophorone diisocyanate (IPDI) cross-linker gave lower cross-linking density and degradation rate to the PU coating compared to hexamethylene diisocyanate (HDI). Cyclic trimer (CT) isocyanate cross-linker gave higher durability compared to biuret (BI). A primary amide and urea entity rich top-film was formed at the surface of degraded PU coatings, with characteristic IR bands at 1640 cm-1 and 1560 cm-1. The decomposition of allophanate in exposed HDI-CT cross-linked PU coating was indicated. The degradation of BI core produced additional urea linkage compared to allophanate. ɛ-caprolactam (Capro) blocked isocyanate gave lower cross-linking density and higher degradation rate compared to methyl ethyl ketoxime (MEKO), and 3,5 dimethyl pyrazole (DMP). The addition of melamine and HALS (less than 5%) improved the durability of PU coatings. The melamine linkage was more sensitive to the degradation compared to the urethane linkage. The higher NCO/OH resulted in more rapid degradation product build-up at the surface of the PU coating in the meantime deterred the decomposition of amide II type linkage. A FTIR peak fitting method was developed for generating degradation index plots, based on the knowledge of degradation chemistry of the PU coatings described above. The degradation rate correlation of the PU coatings exposed in the QUV A test and natural exposure sites including Liverpool, UK (LIV), Vereeniging, South Africa (SA) and Kuala Lumpur, Malaysia (KL) are demonstrated by using degradation index plot methods. The harshness of the natural exposure sites gives the order of KL > SA > LIV.