THE INTERPHASE IN UNIDIRECTIONAL FIBER-REINFORCED EPOXIES - EFFECT ONRESIDUAL 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 t o incorporate a realistic interphasial region into the micro-mechanica l analyses of composite systems. The authors have recently proposed a model for the interphase properties in fiber-reinforced thermosets; th e Young's modulus and coefficient of thermal expansion of the interpha se are assumed to vary as functions of distance from the fiber in this model. In the current study, the authors' model is utilized along wit h a concentric cylinder assemblage analysis for the determination of t he residual thermal stresses in unidirectional fiber-reinforced epoxie s. 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 t he residual thermal stresses.