International audienceThree generations of small diameter ceramic fibres based on polycrystalline silicon carbide have been developed over a period of thirty years. This has been possible due to studies into the relationships between the microstructures and properties of the fibres. A variety of techniques have been employed by research teams on three continents. The fibres are made by the conversion of polymer precursors to ceramic fibres and all three generations are presently produced commercially. The nature of the precursor and the techniques used for cross-linking have been varied in order to optimise both properties and cost of manufacture. It has been possible to improve the characteristics of the fibres as the processes involved in the cross-linking of the precursor fibres have been better understood and the mechanisms governing both room temperature and high temperature behaviour determined. The result is that, although first generation fibres were limited by a low Young's modulus at room temperature and by creep and instability of the structure at temperatures far lower than those limiting the behaviour of bulk silicon carbide, the third generation fibres shows many of the characteristics of stoichiometric silicon carbide. This remarkable improvement in characteristics has been due to a thorough understanding of the materials science governing the behaviour of these fibres which are reinforcements for ceramic matrix composit

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Three types of glass epoxy composites have been studied and water diffu sion leading to saturation has been shown to occur under humid conditions for two of them, the third composite was seen to degrade in the presence of water. It has been found necessary to apply two different models of diffusion to explain the behavior of the first two materials. Both of the theoretical models are based on Fick's law, the first being classical single phase diffusion and the second is a two phase model for the Langmuir type. The material tested were identical except for the resin hardeners which were used which were, diamine, dicyandiamide, and anhydride. The testing conditions, were 0%-100% Relative humidity and 25°C-90°C.