Effects of interphases on the transverse stress-strain behavior in unidirectional fiber reinforced metal matrix composites

In the context of continuum mechanics, the interfaces between the fiber and matrix are often assumed to be perfect. However, in many fiber reinforced composites, the bond between the fibers and the matrix material is not of the perfect kind that can be modeled by a continuity of traction and displacements across the fiber-matrix interface. Instead, the bond is affected across a thin interfacial zone, an interphase, which has distinct properties from the fiber and matrix. In this paper, a framework has been established to characterize the effects of distinct interphases in the study of fiber reinforced composites. On the basis of this framework, a rigorous analysis has been carried out for the transverse normal loading of a unidirectional fiber reinforced composite. It is assumed that such an interphase is created deliberately by coating the fibers with a third phase material. By the use of the finite element method, a numerical analysis for a basic cell provides results for the micromechanical fields of stresses and the macromechanical properties of the composite, with and without partial interphase failure. In addition, an analytical estimation scheme to predict the transverse effective stress-strain relation is developed by using a modified Mori-Tanaka method. Satisfactory agreement between the analytical estimates and the numerical solutions is found.