he influence of fibre aspect ratio on multilive feed ;lass fibre/nylon 6,6 composites has been studied using wo model materials based on extrusion and pultrusion ompounding. Characterisation of the microstructure of hese compounds revealed that the fibre orientation listribution and volume fraction were similar between he compounds, but the fibre length distributions were bund to be different, with the compound produced by lultrusion compounding having the larger mean fibre ispect ratio. The mechanical performance of the two impounds was evaluated in terms of stiffness and trength across a wide range of service conditions using 10th tensile dilatometry and creep deformation. Under ill test conditions, an improved level of mechanical »erformance was seen for compounds with improved nean fibre aspect ratio. Modelling these materials in erms of stiffness and strength also revealed that mproved performance is expected with an improved ibre aspect ratio.
Carbon-Carbon composites (C-C) may prove to be critical materials for high temperature applications, as they retain their mechanical properties well above 2000°C1. The development of a graphitic structure in the matrix of C-C composites is crucial to the understanding of their mechanical properties. To date very few transmission electron microscope (TEM) studies of these materials have been performed: as a result production often occurs without a full understanding of structural changes which occur during manufacture. X-ray diffraction has indicated that the degree of matrix alignment is greater in C-C composites than in the matrix carbon alone given same thermal history, in addition, the matrix graphitisation can occur in an orientation close to that of the long axis of the carbon fibres. These phenomena are thought to be the result of; a) the fibre-matrix interface acting as a nucleation site for graphitic domains forming in the matrix, and/or b) the difference in the coefficients of thermal expansion of the matrix and the fibres being sufficient to cause stresses which encourage graphitisation.
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