Microscopic and Mesoscopic Evaluations of Materials. Analysis of Mechanical Behavior of Short-Fiber Composite using Micromechanics(2nd Report, Effects of Fiber Clustering on Stiffness and Crack Initiation).

Abstract

An injection-molded short-fiber compostie often contains some fiber clusters due to a poor mixing process. An analytical model for a composite with such clusters is developed to estimate a composite stiffness and stresses inside and just outside a fiber of a composite. Firstly the stiffness of the cluster is predicted by applying the Eshelby's equivalent inclusion method to the cluster. 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 Hill-Walpole-Mura's jump condition. It is concluded from this parametric study that the effective stiffness of 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, namely higher stiffness reinforcement, composite is more sensitive to the clusters than a glass-fiber one.