The micromechanical behavior of interphases or interfacial zones in fiber-reinforced composite materials is investigated. Three dimensional models based on elasticity theory are developed for a unit cell, which contains the matrix, fiber and interphase, with or without the presence of an interface crack. An advanced three-dimensional boundary element method with thin-body capabilities is employed which provides more accurate stress data in or near the interphase especially when interface cracks are present. The research enhances the understanding of the micromechanial properties of interphases in fiber reinforced composite materials and facilitate a robust numerical tool in the design of advanced composite materials.
