Coating Sequence Effect for Composites Containing Multiply Coated Long Fibers

Abstract

The effect of coating sequence on the effective conductivity of composites containing multiply coated aligned long fibers, either periodically arranged or randomly distributed, is investigated. The effect is found to be dramatic. Reordering of the coating sequence may shift the coated long fiber from being enhancing to being impairing to the matrix. It is further found that outer coating layers play a more influential role than inner coating layers do in affecting the effective conductivity of the composite since outer coating layers are more exposed to the heat flow. The coating sequence effect is investigated for three different microstructures, namely square arrays, hexagonal arrays, and random arrays, and is most pronounced, at a fixed inclusion volume fraction, for the random array, less for the square array, and the least for the hexagonal array. This observation can be explained in terms of the involvement of relevant dimensionless multipole polarizabilities in the evaluation of the effective conductivity. The present development can also be used to compute the effective conductivity of composites containing either periodically arranged or randomly distributed aligned long fibers possessive of radially changing conductivities. Example calculations are offered to illustrate the converging behavior of this application.