Abstract
Various models are proposed to the composite materials including clusters of reinforcements. In such models, the concentration of reinforcements in the cluster is generally very high or low compared to the outside region of the cluster. However, in realistic composite materials, the difference of concentrations inside and outside of the cluster is relatively small. In the present study, such a low-level clustering of reinforcements is modeled by replacing the cluster with the mixed double inclusion of the first kind by focusing on some reinforcement and smearing out of its surrounding, and by addition of the reinforcements in the matrix region outside of the clusters. As a result, the total internal stress occuring in the reinforcement is different in magnitude inside and outside of the cluster and also that in the matrix is so.
