Thermal stresses in fibrous composites incorporating hybrid interphase regions

A micromechanics semi-analytical method has been developed for the determination of thermal stresses in unidirectional fiber-reinforced composites incorporating a hybrid interphase region. The representative volume element consists of a three phase composite structure subjected to a uniform temperature change. An advanced interphase concept is introduced, in which the interphase thickness varies depending on the particular property under consideration. This model involves also imperfect adhesion by immediate softening of material properties. To treat these features, a regenerative piecewise homogeneous formulation has been developed, which accounts for the spatial variation of the material properties within the interphase region in an averaged sense. Global design variables of this formulation involve geometric and material aspects of the composite. Adjustment of these variables yields parametric studies concerning the thermal stress response. Numerical results are illustrated and discussed for a variety of the involved parameters. Thermal stress and strain concentrations occur in a zone surrounding the fiber, although peak values depend on bonding efficiency and overall anisotropy of the material.