Effective stiffness and thermal expansion coefficients of unidirectional composites with fibers surrounded by cylindrically orthotropic matrix layers

An approach to predict the effective thermoelastic properties of unidirectional composites consisting of cylindrically orthotropic fibers surrounded by layers of cylindrically orthotropic matrix is developed and applied to carbon/carbon composites. Micromechanical modeling is based on elastic solutions for basic loadcases including prescribed axial tension, transverse hydrostatic loading, axial and in-plane shear, and unconstrained thermal expansion. The composite cylinder assemblage model (Hashin, 1990) is utilized to predict axial elastic properties, transverse bulk modulus and thermal expansion coefficients of the overall composite. The effective transverse shear modulus is evaluated using a self-consistent method. The approach is illustrated by considering a representative carbon/carbon material system containing pyrolytic carbon matrix of two different texture levels.