The acoustic emission technique has been used to characterize fatigue damage accumulation in glass fiber woven roving (O/90°) polyester laminates after prolonged exposure in sea water. Comparisons were made with fatigue tests of "as-received" laminate under similar loading conditions. Pre-exposure has been found to substantially reduce the fatigue strength of the composite. Acoustic emission monitoring during fatigue testing has shown that the amplitude distribution of the acoustic events shifts from predominantly low amplitude (40-55 dB), associated with matrix cracking, in as-received specimens, to intermediate amplitude (55-75 dB) associated with delamination and debonding after pre-exposure. Optical microscopy of fatigued samples has verified these failure mode changes. The number of recorded high amplitude events (2 80 dB) associated with fiber fracture is the same in both cases, which indicates that the glass reinforcement is unaffected by pre-exposure.

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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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