THE ANISOTROPY EFFECT ON THE STIFFNESS AND TOUGHNESS OF ENCAPSULATED FIBER COMPOSITES

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 composi te thin sheet was evaluated and provided information for the toughness of the material prior to fracture. A typical composite material was m acroscopically assumed as a transversely isotropic medium, whereas the representative volume element used for its description is formed by a cylindrical fiber of either a transversely isotropic, or a purely iso tropic material, a transversely isotropic cylinderical annulus as coat ing of the fiber, and an annulus of the matrix covering the encapsulat ed fiber. The matrix consisted either of isotropic or transversely iso tropic material, which is further surrounded by the equivalent composi te, which averaged the actual properties of the bulk of the composite containing the dispersed encapsulated fibers. Solutions for the longit udinal and transverse elastic moduli E(Lc) and E(Tc) as well as the sh ear moduli G(Lc) and G(Tc) of the composite are defined in a closed fo rm. Their variation in terms of the relative extent of the matrix is a lso evaluated. Finally, interesting information concerning the variati on of the elastic stiffness of the composite due to anisotropy of the matrix was found. Furthermore, the strain energy density released by a n edge crack in a rectangular composite sheet was determined for the v arious models with anisotropic fibers or matrices studied in this pape r.