The Anisotropy Effect on the Stiffness and Toughness of Encapsulated Fiber Composites

Abstract

The variation of the effective moduli in encapsulated fiber composites, which consist of anisotropic phases, is presented in this paper. The strain energy rate released by an edge crack in a rectangular composite thin sheet was evaluated and provided information for the toughness of the material prior to fracture. A typical composite mate rial was macroscopically assumed as a transversely isotropic medium, whereas the repre sentative volume element used for its description is formed by a cylindrical fiber of either a transversely isotropic, or a purely isotropic material, a transversely isotropic cylindrical annulus as coating of the fiber, and an annulus of the matrix covering the encapsulated fiber. The matrix consisted either of isotropic or transversely isotropic material, which is further surrounded by the equivalent composite, which averaged the actual properties of the bulk of the composite containing the dispersed encapsulated fibers. Solutions for the longitudinal and transverse elastic moduli E_Lc and E_Tc as well as the shear moduli G_Lc and G_Tc of the composite are defined in a closed form. Their variation in terms of the relative extent of the matrix is also evaluated. Finally, interesting information concerning the vari ation of the elastic stiffness of the composite due to anisotropy of the matrix was found. Furthermore, the strain energy density released by an edge crack in a rectangular compos ite sheet was determined for the various models with anisotropic fibers or matrices studied in this paper.

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