Intra-laminar and inter-laminar cracking in GFRP laminates has been studied. The epoxy matrix used gave a transparent composite and was compatible with polyurethane, enabling a modified system (containing 20% urethane) to be investigated in addition to the standard epoxy. Three stacking sequences of quasi-isotropic laminates, (+45/-45/0/90)s, (0/90/-45/+45)s and (+45/90/-45/0)s were tested. Data were obtained for the growth of damage and its effect on laminate stiffness under increasing quasi-static load and as a function of number of fatigue cycles at two different stress levels. Using the transparent systems enabled a more complete set of damage data to be obtained than by previous workers. The damage comprised 90-ply cracking followed by +45 and -45 cracking and then for (+45/-45/0/90)s [and to a limited extent in (+45/90/-45/0)s], delamination. The initiation and growth of damage was examined with regard to matrix type and stacking sequence. The onset of matrix cracking and delamination are both delayed in the urethane-containing laminates; fracture mechanics tests showed that the urethane system was significantly tourer. Moreover, at a given quasi-static stress or number of fatigue cycles the urethane-modified laminates retain a greater proportion of their initial modulus. The stacking sequence influences interlaminar stresses (thereby controlling delamination) and determines parameters such as ply thickness and neighbouring ply orientation which in turn influence intralaminar cracking. Fracture mechanics has been applied to model the initiation and growth of delamination under quasi-static and cyclic loading using a modified compliance technique. Shear-lag models have been used to determine the stiffness loss due to intralaminar cracking, enabling the stiffness reduction associated with delamination to be deduced empirically. This enables the energy release rates associated with delamination to be derived leading to more sensible results than those obtained using an unmodified technique.

Subsea pipelines, as the main transportation means for oil and gas produced offshore, are a key element of the production system. Cathodic protection systems (CPS) are used in combination with surface coatings to protect the pipeline from external corrosion. Although cases of pipeline failure due to external corrosion remain rare, such failures can have catastrophic effects in terms of human lives, environment degradation and financial losses. The offshore industry was led to the use of risk analysis techniques subsequent to major disasters, such as Piper Alpha and Alexander Kjelland. These accidents made the development and use of risk analysis techniques of highly significant interest, and reliability analysis is presently becoming a more important management tool in that field for determining reliability of components such as pipelines, subsea valves and offshore structures. This research is based on an analysis of subsea pipeline cathodic protection systems and on a model of the electrochemical potentials at the pipeline surface. This potential model uses finite element modelling techniques, and integrates probabilistic modules for taking into account uncertainties on input parameters. Uncertainties are used to calculate standard deviations on the potential values. Based on the potentials and potential variances obtained, several parameters characteristic of the cathodic protection system reliability, such as probability of failure and time to failure, are calculated. The model developed proved suitable for simulating any pipeline, under any environmental and operational conditions. It was used as a reliability prediction tool, and to assess the effects of some parameters on the cathodic protection system reliability.

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Cellular materials are widespread. Some, like wood and bone, occur in nature, while others, like polymeric foams, are manmade. Because of their cellular structure, they have unusual mechanical properties: they can be stiff, yet light, and they are capable of absorbing large deflections and thus large amounts of energy. Yet their mechanical behaviour has hardly been studied: no comprehensive attempt to relate mechanical properties to structure exists. In this thesis, we have attempted to do this. We first model a cellular material as a simple, two-dimensional array of hexagonal cells and identify and analyze the mechanisms by which it deforms. From this we calculate the elastic moduli and the elastic and plastic collapse stresses for ideal two-dimensional cellular materials. The results (which we have experimentally verified) show that each of these properties depends on three parameters: a solid cell wall material property, a geometric constant, and the relative density of the cellular material raised to the power two or three. We then examine three-dimensional cellular materials. Because their geometry is irregular and very complicated, no exact analysis of their behaviour is possible. But, with our understanding of two dimensional cellular materials and how they deform, we can use dimensional arguments to analyze three-dimensional cellular materials. The results of this analysis agree well with experimental data. Finally, we have applied our understanding of cellular materials to two case studies. In the first, we have examined the structure of cork, a quasi- two-dimensional cellular material, and explained some of its mechanical properties. The second case study analyzes the problem of material selection in packaging.

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