THE INTERPHASE IN UNIDIRECTIONAL FIBER-REINFORCED EPOXIES - EFFECT ON RESIDUAL THERMAL-STRESSES

The 'Interphase', in a composite, is usually modeled as a homogeneous region, despite the fact that it may have spatial property variations. However, it is important to the understanding of composite behavior to incorporate a realistic interphasial region into the micro-mechanical analyses of composite systems. The authors have recently proposed a model for the interphase properties in fiber-reinforced thermosets; the Young's modulus and coefficient of thermal expansion of the interphase are assumed to vary as functions of distance from the fiber in this model. In the current study, the authors' model is utilized along with a concentric cylinder assemblage analysis for the determination of the residual thermal stresses in unidirectional fiber-reinforced epoxies. The governing field equations in terms of displacements are solved in 'closed form'. It is found that, although the solution is 'dilute', the property variations in the interphase have a distinct effect on the residual thermal stresses.