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The diffusion of water in an isophthalic polyester glass reinforced composite laminate, typical of marine applications, has been studied through accelerated water uptake tests involving total immersion in seawater at 40 and 60uC. Gravimetric analysis has shown that at 40uC, a Fickean type diffusion is operative with a saturation level of 0?8% whereas at 60uC, a two stage Langmuir type diffusion is operative. The nuclear magnetic resonance technique has also been used in an attempt to image the diffused water and determine its position within the composite. This has revealed that the water concentrates on the fibre/matrix interface and the concentration there is twice that of bulk of the matrix. The diffusion process appears to be aided by 'wicking' along the fibre/matrix interface.

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There are many instances where the use of weight saving composite materials for an entire structure is either; too complex, too expensive or unfeasible. In these circumstances the use of a hybrid structure can incorporate the benefits of traditional construction materials, for example steel, coupled with the advantages of composite materials in weight critical areas. In the present study, an investigation was undertaken into the fatigue life characterisation of a hybrid joint for marine application. In addition the residual strength of the joint, after a fixed number of fatigue cycles, was assessed under axial compression and bending loads. A progressive damage model was developed to predict the location of major stress concentrations, the path of damage and subsequent loss in stiffness of the joint under axial compression.

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