BOUNDS ON THE EFFECTIVE THERMAL-EXPANSION COEFFICIENT OF A POLYCRYSTALLINE AGGREGATE

The present study establishes bounds on the effective thermal-expansio n coefficient monocomponent isotropic polycrystalline aggregate with c rystallites having a preferred uniaxial axis (tetragonal, trigonal, an d hexagonal) using multiple scattering theory (MST). The expression of alpha using MST for such polycrystals is a monotonically increasing (or decreasing) function of the effective bulk modulus K. This provid es a means to predict bounds on alpha using the bounds on K*. MST has been used to derive, first, the third-order bounds on K and, second, the t-matrix bounds, which are even stricter. Both these bounds are, however, narrower than the Voigt-Reuss bounds. Finally, the formulas o btained have been used to calculate bounds on alpha in the case of po lycrystals belonging to symmetry classes listed above, and the results obtained are found to compare favorably with observations. (C) 1995 A merican Institute of Physics.