THE INTERPHASE IN UNIDIRECTIONAL FIBER-REINFORCED EPOXIES - EFFECT ONLOCAL STRESS-FIELDS

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 micromechanical analyses of composite systems. The authors have recently proposed a m odel for the interphase properties in fiber-reinforced thermosets; the Young's modulus and coefficient of thermal expansion of the interphas e are assumed to vary as functions of distance from the fiber in this model. In the current study, the authors' model is used along with Mor i-Tanaka analyses for the determination of ''nondilute'' local stress fields in unidirectional fiber-reinforced epoxies under thermomechanic al loading situations. The governing field equations in terms of displ acements are solved in ''closed form.'' It is found that property vari ations in the interphase have a distinct effect on the local stresses. This is significant, considering the fact that local stresses play an important role in controlling the structural performance of a composi te. The ideas behind this study can be extended to characterize and an alyze the interphase in metal matrix and ceramic matrix composites.