Analysis of Mechanical Behavior of a Short Fiber Composite Using Micromechanics Based Model. Effects of Fiber Clustering on Composite Stiffness and Crack Initiation.

Abstract

An injection-molded short fiber composite often contains some fiber clusters due to a poor mixing. An analytical model for a composite with such clusters was developed to estimate a composite stiffness and stresses inside and just outside a fiber of the composite. In this paper, first the stiffness of the cluster is predicted by applying the Eshelby's equivalent inclusion method. Secondly the stiffness of the overall composite and the stress inside a fiber are assessed by applying the Eshelby's method to two kinds of inhomogeneities, i. e. cluster and fiber. Finally the stress just outside the fiber, namely the fiber-end stress, is evaluated using the Hill-Walpole-Mura's jump condition. It is concluded from this parametric study that the effective stiffness of a short fiber composite tends to decrease as the volume fraction of clusters increases, and cracks at fiber ends are more likely to occur at a lower applied stress level as the volume fraction of clusters increases since the magnitude of the fiber-end stress increases. It is found that a carbon fiber composite with higher stiff reinforcement is more sensitive to the negative effects of fiber clustering than a composite with less stiff reinforcement.