3D electrical percolation behavior in conductive short fiber composites

Abstract

The percolation behavior and electrical conductivity in unidirectional composites made of short conductive fibres embedded in an insulating matrix were examined by Monte Carlo simulation as a function of aspect ratio, volume fraction and angle. The percolation threshold did not change as the fibre length distribution. The electrical conductivity increased exponentially with volume fraction and the exponent increased as the aspect ratio increased for isotropic composites. The unidirectional composite exhibited a highly anisotropic percolation behavior with respect to the fibre direction for both fibre normal and fixed length distribution. For the direction parallel to fiber, the electrical conductivity increased exponentially with the volume fraction and the exponent increased as the aspect ratio increased. However, the conductivity in the transverse direction exhibited a sharp transition, from zero to nearly the same level as parallel conductivity at the critical volume fraction. The percolation threshold for the transverse direction also increased with aspect ratio up to 20, above which it decreased in parabolic manner. Both the threshold volume fraction and transient increase in the conductivity for the transverse direction varied parabolically with aspect ratio, the maximum being an aspect ratio of 20. On the basis of the agreement we proposed a new percolation model to account for the electric percolation of conductive short fiber composites. The percolation behavior and electrical conductivity calculated by this formular showed good agreement with that of experimental results.