The procedure for determining a homogenized Young’s modulus of a 3-D orthogonal carboncomposite composite is laid out. X-ray tomography is performed to determine the dimensions of bundles and defects in the composite after manufacturing. Voids, intra-bundles, inter-bundles and interfacial cracks are visible in the scanned images. Push-out and pull-out tests are performed on composite specimens and a shear lag model is used to determine the interfacial fracture energy. These tests are then simulated by a finite element model with cohesive elements used to represent the interface. An iterative approach is used to determine the fracture energy, shear strength and coefficient of friction of a cohesive zone model. These properties are next used in the analysis of a unit cell with periodic boundary conditions for determining the Young’s modulus. The unit cell of the 3-D composite is obtained from tomography images, although a number of features have been neglected during the analysis to keep computations manageable.