Aligned fibre composites transverse properties

One common characteristic of all C/SiC composites is their distinct anisotropy in the mechanical as well as thermophysical properties. Considerable lower values of the tensile strength and the strain to failure have to be considered for an appropriate design if the load direction and the fibre alignment are not congment. As the carbon fibres show a different physical behaviour in longitudinal and radial direction, the composite s properties like thermal conductivity and coefficient of thermal expansion differ widely with respect to the in-plane or transverse direction. 

The properties of the composite are affected by fibre and matrix type, the relative quantity of each in the composite and the directionality of the fibres. A composite which has all the fibres aligned in one direction, i.e. is uni-directional, is stiff and strong in that direction, but in the transverse direction it will have low modulus and low strength. 

In a transversally isotropic material, there is a plane in which all properties are isotropic. Perpendicular to this plane, the properties differ. One example for such a material is a hexagonal crystal which is transversally isotropic with respect to its mechanical properties.Other technically important materials may also be transversally isotropic, for example directionally solidified metals in which the grains have a preferential orientation (see also section 2.5), or composites (chapter 9) with fibres oriented in one direction, but aligned arbitrarily (or hexagonally) in the perpendicular plane. 

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