This paper describes an analytical method for evaluating the elastic properties of three-dimensional fiber reinforced composite materials on the basis of a micromechanical analysis of a unit cell structure. The unit cell is a small repeating geometrical unit of fiber bundles. A special feature of this study is to treat the unit cell as a rigid frame structure constructed of fiber-beam and matrix-beam elements. This analytical structure model can faithfully represent actual fiber composition. For two types of carbon/epoxy three-dimensional composite test pieces cut out of I-beam structure, the tensile elastic moduli are computed by finite element method. Comparisons between analytical and experimental results are also made. This analytical method shows good agreement with the experimental data.
