Characterization of Tree Growth in Inorganic-filler/Epoxy Resin Composite Material

This paper presents the structural characterization of treeing phenomena of a micro-composite material, composed of micro-size inorganic silica filler added to epoxy resin. The fractal dimension of the electrical tree and its relationship with filler content was determined. The damaged area of tree in various contents of filler was also estimated. Furthermore, the lacunarity of tree with identical fractal dimension was calculated as a complement of fractal dimension characterization. It is concluded that the existence of filler makes the tree structure more complicated by introducing obstacles to tree propagation, leading to the high fractal dimension of the tree. In addition, it was found that the fractal dimension of the tree was very relational to the fractal dimension of the composite material including filler particles. On the other hand, the lacunarity of without-filler specimen would be lower than that of in with-filler specimen. It is considered that the tree growth in with-filler specimen would have "localized-branching" at the interface between filler and resin. The more filler content, the more localized-branching occurred, leading to the heterogeneous inherent structures of the trees