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Section A Some Aspects of Three-Dimensional Photo-Elastic Stress Analysis. The theory of Photo-Elasticity is discussed, both for two and three dimensional stress problems. An investigation is carried out showing that Catalin 800, with certain reservations, is suitable for three-dimensional stress analysis. Certain three-dimensional stress problems are investigated with reference to pressure on part of the boundary of semi-infinite solid. Section B1 An Investigation of the Stresses found in a semi-infinite body of sand acted upon by pressure on part of the boundary. A circular plate is loaded and the stresses in the sand investigated a pressure cell capable of giving the Principal Stresses. The stresses so found are in accordance with the hypothesis that the sand can be considered as an idealized solid which obeys Hooke's Law but is horizontal direction. Section B2 An Investigation of The Variation of Subgrade Modulus of a Sand with Varying Beam Breadths. A Foundation Beam is loaded and the relationship between contact pressure and deflection is found. This relationship, the Subgrade Modulus, is found to have a constant value for the majority of practical engineering problems.

The use of fibre reinforced polymers is rapidly increasing in a range of applications, from aviation to sporting goods. While the outstanding material properties offered by modern composites make them widely applicable they often suffer from brittle, catastrophic failure. Their inherent brittleness limits their application for safety critical applications without large safety margins. This thesis sets out to introduce design principles that introduce a degree of 'pseudo- ductile' failure behaviour to advanced fibre composites. Much of the inspiration for the work comes from looking at the failure processes of natural hierarchical materials. Many of these materials are able to sustain large amounts of damage at different length scales without catastrophic failure, with many of them being essentially ceramics. Nacre, a relatively simple discontinuous laminated material, served as a major inspiration. Three main strategies were employed to reduce the effects of brittle fracture. Ply terminations were used to selectively weaken a laminate allowing one large fracture to be replaced with a number of smaller ones. Thereby giving indication of the laminates failure and significantly increasing the strain to failure over a traditional laminate. Ply perforations, where portions of a ply are cut, were used to weaken a laminate allowing the location of the fracture to be controlled. The third method tailored interlaminar fracture toughness allowing for steady crack propagation where traditional laminates would suffer unstable crack growth. The work introduces three distinct and highly expandable methodologies capable of reducing the limitations of modern composites.

The rheology of a two-dimensional dry foam is probed with quasi-static bubblescale simulations of the sedimentation of circular discs and elliptical objects. The sedimenting objects move in response to a combination of their weight and the forces exerted on them by the network of soap films and the pressures in the bubbles. Viewed macroscopically, the plasticity and elasticity of the foam combine to determine the rate of descent of a circular disc. A critical disc weight is found that determines whether the disc is supported by the foam or not. This critical weight increases linearly with disc diameter and decreases with the liquid fraction of the foam with a power-law relation. Similarly, the drag force exerted on a disc increases linearly with its diameter and decreases with the liquid fraction of the foam with a power-law relation. An attractive force between a disc and a nearby wall is seen when the disc is further than two bubble diameters from the wall. Such wall effects are minimal when the disc sediments from a central position in a channel of sufficient width. The interaction between two sedimenting discs is quantified by placing them in one of two configurations: one in which the discs are placed side by side and the other in which the discs are initially one above the other. The discs descend through the foam and move towards a stable orientation in which they are positioned directly above one another with a constant separation of one or two bubbles. Above a critical initial separation of the order of 5 bubble diameters, the discs do not interact. The existence of the critical separation is shown to be a result of the discrete nature of a dry foam. The descent and rotational motion of an ellipse of similar size and weight to one of the circular discs is then considered. An ellipse rotates towards a stable orientation in which its major axis becomes parallel to gravity, driven by the local structure of the foam. This rotational motion is much slower than the downward motion.

In this work, X-ray techniques have been used to study coatings of zirconia and yttria doped zirconia. The experimental techniques used were laboratory-based X-ray diffraction (XRD) and synchrotron radiation based small-angle X-ray scattering techniques in both transmission mode; small-angle X-ray scattering (SAXS), and reflection mode; grazing-incidence small-angle x-ray scattering (GISAXS). By using XRD and (GI)SAXS measurements, information has been gained about the crystal structure of the coatings, and about the size- and surface structure of the scattering particles, respectively. Two types of in situ experiments were performed; in situ dipping-and-heating cycles, and in situ incremental heating. SAXS was used for the measurements on the former, whilst both SAXS and GISAXS was used for the latter. The coatings have been studied at various stages during calcination, and a novel methodology used for tracing the morphology quantitatively in systems subject to change, is presented here. This type of measurement and methodology is important, for example, in understanding mechanisms of corrosion and catalysis or ageing of materials. I found that the coatings transform from polymeric gels to particulate films featuring agglomeration and Ostwald ripening, as the sample is heated. The yttria concentration was found to influence the size- and the surface structure of the scattering particles; the more yttria, the smaller particles. When the samples were heated, I found that the particles within the coatings with higher yttria concentration gets a rougher surface structure at lower temperature than the particles in the lower yttria concentration coatings.

Electrochemical techniques are used to investigate a variety of novel and natural cellulose materials. Novel cellulose architectures are formed using electrodeposition of cellulose microfibrils (from spruce tree) and by the layer-by-layer deposition or solvent casting of cellulose nanofibrils (from sisal). Pure cellulose (with a crystal structure of cellulose-I) constitutes the majority of all architectures, however additional properties were incorporated via the addition of polymers (polydiallyldimethylammonium chloride, chitosan), nanoparticles (TiO2) or binding molecules (boronic acid dendrimer). Cotton fabric, a natural form of cellulose, was also investigated via the physical attachment to the electrode surface of graphite flake modified cotton samples using a course lycra membrane. All samples are characterised using a combination of scanning electron microscopy, atomic force microscopy and small and wide angle x-ray scattering. The absorption, diffusion and detection of charged species in cellulose materials is studied using voltammetry under aqueous conditions. Firstly, architectures are probed using charged metal species like Fe(CN)63-/4- and Ru(NH3)3+/2+ in order to construct a model of diffusion and absorption. Later, target analytes such as environmental molecules (triclosan, sodium dodecylsulfate) and physiological type molecules (alizarin red S) are detected within a typical range of 10-6 – 10-3 M. Approximations of Fick’s Laws are used to calculate membrane diffusion co-efficients. Langmuir type binding is assumed and the binding of species in the cellulose architectures is quantified. The reactivity of molecules in cellulose matrices is studied. Methyl viologen (MV2+/+) is shown to form aggregates in when partitioned in a cellulose environment. Methemoglobin undergoes a novel demetallation when in a charged nanocellulose-TiO2 matrix. The reactivity of a well-known catalase model system, the dinuclear manganese metal complex [Mn(IV)2(μ-O)3L2](PF6)2 (with L = 1,4,7-trimethyl-1,4,7-triazacyclononane), is shown to be affected by the presence of a cellulose matrix.

The principal aim of this thesis is to analyse the effectiveness of multifunctional smart materials as intelligent structures to improve mechanical properties and activate additional non-structural features. In order to investigate these multiple aspects, a comprehensive literature review has been presented focusing on the state of the art in multifunctional and smart materials. From this analysis, five different systems based on different designing solutions and manufacturing techniques were developed and experimentally validated. Multiscaled composites are a typical example of multifunctional materials and are based on the addition of engineered nanoscaled reinforcement to traditional mesoscopic systems. To test the effectiveness of nanomodification, an experimental campaign has been carried out, aimed to the characterisation of a nanocomposite obtained embedding Graphene Nanoplatelets (GNPs) in the polymeric structure of Low Density Polyethylene films at difference concentrations. Nanoscaled fillers were subsequently used to manufacture a threephasic multi-scaled composite based on the inclusion of nanometric SiO2 particles in a traditional carbon fabric/epoxy system. Following a different approach, hybrid structures with embedded Non-Newtonian fluids have been manufactured and tested and the results showed that nonlinear viscosity can be exploited to dynamically enhance material properties during an impact event. The possibility to intervene both on structural and non-structural properties has been investigated with another hybrid system, based on the embodiment of Shape memory Alloys (SMA) wires within a traditional unidirectional CFRP. The study of the impact properties pointed out that the superelasticity effect and the hysteretic stress/strain behaviour of the embedded wires reduce the extent of the internal delamination for samples subjected to low velocity impacts. Moreover, by exploiting the SMAs thermoelectrical properties it is possible to use the embedded metallic network as a strain sensor by measuring the electrical resistance variation and as an embedded heat source to be used for rapid thermographic damage location and evaluation.

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Permeability of hardened cement paste (hcp) was studied in relation to the modes of change in pore structure due to hydration and water/cement (w/c) ratio. The effects of the addition of aggregate to hcp on permeability of mortars were studied in this thesis. The saturated permeahility was measured by a steady-state method which takes advantage of the do$tc prSJrC in sealing truncated conical disc specimens at pressures up to 2000 psi. Complementary measurements of the pore size distributions by mercury porosimetry, total porosities by helium comparison pycnometry and the evaporable water contents at 105°C were made to characterise the pore structure of hardened cement paste and mortars. The purpose was to identify the most appropriate variable(s) of the structure of hcp and mortars that relate(s) to permeability. It was found that although the permeability of hcp increases with increasing total porosity, permeability is a multivalued function of total porosity and depends on whether the change in porosity derives from changes in water/cement ratio or times of hydration. It was possible to identify, from the pore size distributions, a primary continuous pore radius, which is thought to correspond to the maximum spacing between the weakest links in the bonds of cement hydration products. It was found that permeability of hardened cement paste was closely and uniquely related to the primary continuous pore radius irrespective of whether the mode of change in pore structure results from differences in water/cement ratio or times of hydration. The measurements of permeability of mortars prepared with both normal and lightheight aggregates indicated no substantial differences in permeability for the to types of aggregate inclusions in the pastes. It was found that the addition of aggregates of lower total porosity than the paste to the pastes reduce the total porosity of mortars but increase permeability as the volume concentration of the aggregate increases. Suggestions for future work include further measurements of the effect of aggregate additions to pastes at different levels of paste porosity on permeability. Measurements to elucidate the fundamental relationship between the primary continuous pore radius and compressive strengths and elastic constants of hardened cement paste, and their relationships with the nature of the cement hydration products.

A serious disadvantage of composite materials. in general. is their weakness transverse to the fibre direction. In filament wound composite vessels such cracking can lead to the weepage of the vessel contents. The aim of this work was to identify the micro-mechanisms involved in transverse cracking and other, more general. composite failure modes. In this way. a more thorough understanding of the nature of fibre-resin interactions and the role of the matrix in laminate deformation behaviour has been reached. Sections of filament wound pipe tested in either a 2:1 Hoop/Axial stress ratio or a uniaxial Hoop stress were examined m lc roscop lce lly , Weepage at low fibre stress levels was possible by the interaction of many transverse cracks in each lamina. Where transverse cracks did not form prior to failure. weepage was possible by the interaction of inter- and intra-lamina cracks. The change in cracking modes found in the pipe wall, as the in-plane stress condition varied. agreed well with theoretical predictions. Matrix flexibilization improved the biaxial weepage performance of the pipes by inhibiting transverse cracking. Transverse failure was by resin crazing. in regions of closely packed fibres, rather than by fibre debonding. The cri terion for crack suppression being a non-elastic matrix stress-strain response. The propagation of transverse cracks through uni-directional composites was studied under the microscope. In certain cases, cracking was foun d to be controllable, gradual fibre-resin separation was followed by massive non-linear deformation of the inter-fibre resin ligaments. The roles of fibre volume fraction and matrix type were also examined Failure modes in finite width, angle-plied, filament wound rings were studied using the "Split 0 Test". Three failure modes were identified depending on the fibre angle. Below 40 degrees failure was predominantly by transverse cracking and was virtually width independent. Above 50 degrees, failure was by the catastrophic unpeeling of the laminations from the edges, this gave rise to highly width dependent failure stresses. Between these limits, width dependent, mixed mode failure was found. The micro-mechanisms of failure were followed by the examination of pre-pol ished ring edges, after loading, and by pulling very thin polished sections of rings under the microscope. Microscopic resin non-linear deformation, particularly that of the thin interlamina resin layer, was a feature of all the mechanisms observed. It was the ability of this layer to sustain high shear strains which enabled large-scale laminate non-linearity to take place, especially, in the angular range for mixed mode failure between 45 and 50 degrees