Non Hookean Behaviour in the Fibre Direction of Carbon-Fibre Composites and the Influence of Fibre Waviness on the Tensile Properties

In the literature the tensile behaviour in the fibre direction of unidirec tional carbon fibre reinforced plastic (c.f.r.p.) is assumed to be linearly elastic up to failure. Some authors distinguish a primary and a secondary part in the stress- strain curve each showing Hookean behaviour. The experimental results of this paper show that Young's modulus of laminates increases proportionally with the tensile stress, as found in Ref. [1] for single non-impregnated fibres. An empirical relation between Young's modulus and the tensile stress is derived and the influence of fibre misalignment on this relation is exam ined. In addition, the influence of fibre misalignment on the tensile strength and Poisson's ratio is discussed.