The influence of the elastic properties and dimensions of coatings on the stiffnes of encapsulated fiber composites

The effect of coating around fibers embedded in an isotropic matrix on the stiffness of the composite, due to the variation of the coating thickness and rigidity, is examined in this paper. The model of the representative volume element (RVE) of the composite consisted of a cylindrical fiber coated by an annular layer, the encapsulated fiber being embedded in a matrix annulus enveloped by an infinite region of an equivalent composite, which constitutes the rest of the composite. This model constitutes an extension of the Christensen and Kerner models. By varying the rigidity and the thickness of the encapsulation, the longitudinal, transverse and shear elastic moduli of the composite were determined. Interesting results concerning the composite stiffness were established by selecting types of composite having different rigidities for the constituent phases. Furthermore, specific examples of encapsulated fiber composites usually encountered in applications were considered where the properties of the composite are changed by the sizing effect due to encapsulations.