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Composite mechanical properties for use in structural analysis

By Martyn Keith Pinfold


In order to be able to undertake an analysis of a component the designer will\ud need to know the properties of the material being used. The aim of this work is help\ud the design engineer such that the mechanical properties of continuous glass fibre\ud reinforced composite material can be determined and used in the design analysis of\ud components manufactured from this material.\ud The literature survey has shown that for the material considered here, then\ud given the constituent properties, the fibre arrangement and the fibre volume\ud fraction, the composite mechanical properties may be determined mathematically\ud by the use of micromechanical equations. The micromechanical prediction of the\ud mechanical properties of uni-directional, random and woven fibre reinforced\ud composites has been examined. The variation of these mechanical properties that\ud may occur in a composite component due to the manufacturing process has been\ud highlighted as being of importance. This has been studied to determine whether\ud such a variation is significant by analysing examples of composite components and\ud plates. The results from these analyses have been correlated with experimental\ud results and investigated to study the importance of such variations in properties.\ud Many micromechanical equations have been found in the literature for the\ud prediction of the mechanical properties of continuous fibre reinforced composite\ud materials. An accuracy of the predicted properties to within 10% of the\ud experimental data was concluded to be acceptable and good enough for initial\ud design purposes as design engineers are not usually able to design to such tight\ud tolerances. This work has shown that further development of the micromechanical\ud theories is not the most important problem concerning the prediction of the\ud mechanical properties. These properties can currently be predicted with\ud acceptable accuracy from the micromechanical equations already available in the\ud literature. However, the design engineer is unlikely to have knowledge of the\ud micromechanical equations necessary to determine the required properties. It is\ud only by undertaking a large literature survey that the designer would be able to find\ud this information. Many of the micromechanical equations require the use of an\ud empirical factor. The knowledge of a value for such a factor is again something that\ud would not be readily available to the designer. Rather than concentrating upon\ud improving the micromechanical predictions, this work shows that effort should be\ud made to understand the influence of other factors upon the mechanical properties\ud of composite materials. In particular, the behaviour and flow of the material during\ud the manufacturing process has been highlighted as being of importance as it can\ud cause a significant variation in the properties. Thus, analyses of composite\ud components cannot assume that the mechanical properties are constant\ud throughout, and it is therefore necessary to first model the manufacturing process\ud to determine the mechanical properties before undertaking a structural analysis

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