The Elastic Longitudinal Modulus and Poisson's Ratio of Fiber Composites

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Abstract
A simplified theoretical approach for the prediction of the longitudinal elastic modulus and Poisson's ratio in fiber-reinforced composites is developed in this paper. The method considers that the main parameter affecting the elastic behaviour of com posite materials is the existence of the mesophase layer, between fiber and matrix, which possesses different physico-chemical properties than those of the constituent phases. The simplest and most convenient laws of variation are a linear, a parabolic, a hyperbolic and a logarithmic variation of E, and v, for the mesophase material, versus the polar radius from the fiber-surface. In this paper, therefore, these laws are con sidered for evaluating the overall moduli of the composite. Each one of these laws is applied to the representative volume element of the fiber composite and compares favorably with the unfolding model, introduced by one of the authors (PST), as well as with respective data existing in literature.