The Mechanical Properties of Fibre Reinforced Composite Plates

Abstract

The manufacture of composites reinforced with strong, stiff fibres is now a well established practice. The use of glass fibres allowed the theory developed for plywood and similar materials to be used directly as it was assumed that glass fibres were elastically isotropic. Carbon fibres are now used in increasing quantities and the same theory is often used to calculate the mechanical behaviour of carbon composites. It is now known that carbon fibre is highly anisotropic and thus may preclude the use of conventional theory suited to isotropic fibres. This thesis is a study of the effects of fibre anisotropy on the elastic properties of composites. The introduction covers the development of carbon fibres leading to the production of anisotropic fibres, with particular interest in the attempts to calculate the properties of the fibres. The question of the isotropy or otherwise of glass fibres is considered, and it is concluded that glass fibres are isotropic. The properties of composite constituents are determined and used to calculate the properties of unidirectional composites. The properties of the unidirectional composites are measured, compared with the calculated values, and used to predict the properties of laminated composites. The calculated and experimental values of the laminate properties are compared. It is concluded that the properties of laminates may be predicted reasonably accurately from the unidirectional composite properties, but only some of the unidirectional composite properties can be predicted with reasonable accuracy from the constituent properties.