EFFECT OF INTERFACIAL CHARACTERISTICS ON EFFECTIVE CONDUCTIVITIES OF COMPOSITES CONTAINING RANDOMLY DISTRIBUTED ALIGNED LONG FIBERS

The effect of interfacial characteristics on the effective thermal con ductivity, k(eff), of composites containing randomly distributed align ed long fibers is studied. An expression for the reduced effective the rmal conductivity, k(eff)/k(1), is derived with pair interactions rigo rously taken into account. Two types of interfaces are treated: one wi th finite thickness and one with no thickness but possessive of certai n thermal barriers. The expressions of k(eff)/k(1) for these two types of interfaces are found to be identical but with different definition s for involved multipole polarizabilities, theta(n). The effect of int erfacial characteristics, quantified as the relative interfacial thick ness, delta/a, reduced interfacial thermal conductivity, sigma(3), and Blot number, Bi, on k(eff)/k(1) is thoroughly investigated. It is fur ther found that interfacial characteristics may be well represented by the dipole polarizability, theta(1), although higher orders of multip ole polarizabilities appear in the expression of k(eff)/k(1). Comparis on of the present results with those obtained from three less rigorous models, the equivalent inclusion model, modified effective medium the ory, and modified Hashin and Shtrikman's bounds, is also presented. Th e present results stay well within the bounds for the combined area fr action of interface and inclusion, f, up to 0.5. Finally, the effect o f microstructure on k(eff)/k(1) is examined by a comparison of present results with those for square and hexagonal arrays. The randomness in configuration tends to intensify the thermal interactions between the effective inclusion and the matrix such that, under the same conditio n, k(eff)/k(1) values of the random array deviate farther from unity t han those of the regular arrays. Copyright (C) 1996 Elsevier Science L td