Visco-elastic stress distributions and elastic properties in unidirectional composites with large volume fractions of fibers

In this work, the visco-elastic stress distributions and elastic properties of unidirectional graphite/polyimide composites have been examined as a function of the volume fraction of fibers. The stress distributions were determined by employing two different methods, namely the finite element method (FEM) assuming either hexagonal or square fiber arrangements, and the Eshelby method modified by Mori and Tanaka to account for the presence of multiple fibers. It has been presented in this research that the Eshelby/Mori-Tanaka approach can be used for the calculations of the stresses inside and outside graphite fibers provided the volume fraction of the fibers does not substantially exceed 35% in the case of the square fiber array and 50% for the hexagonal fiber distribution. It has also been shown that the elastic proper-ties of unidirectional graphite/polyimide composites can be accurately determined using the analytical Eshelby/Mori-Tanaka method even for large volume fractions of fibers. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.