The effective thermal conductivity of composites with coated reinforcement and the application to imperfect interfaces

An analytical model is developed to predict the effective thermal conductivity of multiphase composites reinforced with coated fillers. The coated fillers are modeled as confocal spheroids, thus enabling the simulation of a wide range of reinforcement geometry ranging from thin flake to continuous fiber. The orientation of the coated fillers is described by a density distribution function which can simulate completely random, in-plane random, and aligned distributions as special cases. The analytical approach appears to be the only one in the literature that renders closed-form predictions of the effective thermal conductivity of composites with misoriented coated reinforcement and thus recourse to a numerical scheme is not required. The analytical approach is specialized to consider the effects of a thermal resistance at the filler-matrix interface of a composite. Results of the proposed model are compared with those obtained by self-consistent and differential estimates Y. Benveniste and T. Miloh, J. Appl. Phys. 69, 1337 (1991) for the effective thermal conductivity of a composite reinforced by completely random coated short fibers. The proposed model is in close agreement with the other two models for low conductivity coatings, but differs appreciably for high conductivity coatings. Finally, good agreement is shown to exist between analytical predictions and experimental results obtained from the literature for a diamond particle/zinc-sulfide matrix composite with an interfacial thermal resistance.