| Summary: | A comprehensive study of the fatigue behaviour of a polyurethane acrylate resin and glass fibre reinforced composites has been undertaken. In the first part, three types of resins were tested: polyurethane vinyl ester, polyester and polyurethane acrylate, which was formulated to have superior properties. Three different types of glass fibre cloth were used for reinforcement, a woven roving and two novel stitch bonded Ulticloths. The [0/90]2s and [+/-45]2s lay-ups were prepared in order to investigate the effects of matrix, cloths and lay-up on fatigue strength and life time. Polyurethane acrylate composites proved to be superior to the polyester resin. The study on damage mechanisms also showed that the first damage was matrix cracking followed by interfacial failure, debonding, delamination and fibre facture which accumulate from the initial cycles until failure. The second part of this study concentrated only on polyurethane acrylate resin reinforced with Ulticloth [90/0]2s and Biaxial Ulticloth [+/-45]4 lay-ups. The data were produced to compare the effect of environment such as air, distilled water and seawater on the composite with tension-tension and tension-compression loading. With the [90/0]2s lay-up the fatigue strength and lifetime were reduced by the presence of distilled water and seawater. Once again, during fatigue testing with R=0.1, microscopic observations showed that these composites suffered severe damage. Samples tested in seawater had more damage compared with samples tested in air and distilled water. The last part of this research was to investigate the modulus degradation during the fatigue life. This investigation revealed that the modulus degradation on all laminates was dependent on stress ratio and lay-up. The modulus of [90/0]2s lay-ups was degraded during fatigue tests and this modulus degradation curve could be divided into three stages. The most clear damage occurring in [+/-45]4 was delamination which happened at both types of stress ratio, R=0.1 and R=-l. Analysis of some microscopic fractography has been carried out to support the observations.
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