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To obtain creep-rupture data at low level within a reasonably short time-scale, two accelerated techniques have been investigated. Stepped Isothermal Method (SIM) testing involves loading a single specimen, under constant load, with the temperature increased in a series of steps to accelerate the creep. Careful choice of the temperature step and step duration allow the test to be completed in about 24 hours. At each temperature step a creep curve is obtained; these are then adjusted to compensate for the different temperature levels and a creep master curve at a reference temperature is produced. In Stepped Isostress Method (SSM) testing, a similar approach is adopted but the acceleration is obtained by increasing the stress in steps while keeping the temperature constant. Additional stress provides energy to the system in an analogue of the effect of heat in SIM. In this thesis, SIM and SSM tests have been successfully applied to two slightly different aramid fibres, Kevlar 49 and Technora, for a wide range of loads (50-80% ABL). The test data are used to determine the creep and creep-rupture behaviour of the two materials. The creep master curves obtained by accelerated testing are compared with conventional creep tests at ambient conditions, and good agreement of the data is observed. A rheological model for the prediction of the creep and creep-rupture of the two fibres is established to facilitate and greatly increase the reliability of the prediction of the long-term behaviour. This investigation allows more certainty about the creep-rupture relationships for different high modulus fibres, which will in turn allow more realistic safety factors to be applied when using these materials in engineering applications.

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The power units in modem electric vehicles are required to store large amount of energy and to provide a high power. Supercapacitors being able to export a pulsed high power can be used in combination with batteries or fuel cell to meet the energy and power demand of electric vehicles. Carbon nanotubes with high surface area and conducting polymers with large pseudocapacitance are both powerful candidates for supercapacitors. This thesis describes a novel electrochemical route for synthesis of composites of conducting polymer and nanotubes via co-deposition from solutions containing ionic CNTs and monomers. The resulting deposits exhibited a unique porous network structure composed of individual nanotubes coated with a layer of conducting polymers. Carbon nanotubes served as charge carriers during the polymerisation and also acted as both a strong backbone and effective dopant within the composite materials. Therefore, the composites have improved mechanical integrity and an open structure that facilitates ion and solvent motion during the electrochemical processes. Moreover, the large immobile CNT anions exert an electrostatic repulsion to the electrons on the polymer chain. This repulsion makes it easier to remove electrons from the polymer chains. As a result, the composites showed good conductivity and capacitive properties even at negative potentials. A systematic study on the charge storage properties of the composites has been carried out using various electrochemical methods, including CV, AC impedance spectroscopy, chronocoulometry, chronoamperometry and chronopotentiometry. FTIR and XPS have been used to study the interaction between CNTs and conducting polymers. Prototype supercapacitors were built with the composites as electrode material. Both symmetric and asymmetric prototypes showed ideal capacitive behaviour, indicating a good potential for application in supercapacitors using the novel composite materials.

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