EFFECT OF COATINGS WITH SMOOTHLY CHANGING TRANSVERSE RIGIDITIES ON THE STIFFNESS OF ENCAPSULATED ANISOTROPIC FIBER COMPOSITES

The beneficial role of anisotropic coatings with radially dependent tr ansverse stiffness on the improvement of the whole stiffness of the fi ber composite is presented in this paper. Such a typical composite is studied as being, macroscopically, a transversely isotropic material b y arranging the variation of the effective moduli in its respective re presentative volume element. This model is formed by a transversely is otropic cylindrical fiber, a transversely isotropic cylindrical annulu s as coating of the fiber and an annulus of isotropic matrix covering the encapsulated fiber. The material surrounding the matrix, called th e equivalent composite, corresponds to a fictitious material equivalen t of the matrix together with the rest of the fibers included in the r eal composite and therefore attains effective moduli, which average th e actual mechanical properties of the composite. Solutions are establi shed in a closed form for the longitudinal and transverse elastic modu li, E(Lc) and E(Tc) of the composite, and for the shear modulus, G(Tc) , for various composite models. The study of the variation of these me chanical properties in terms of the percentage amount of the matrix re veals interesting information concerning the overall stiffness of the composite, which is influenced by the extent, as well as by the mechan ical properties of the coatings.