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

The present study establishes bounds on the effective thermal-expansion coefficient monocomponent isotropic polycrystalline aggregate with crystallites having a preferred uniaxial axis (tetragonal, trigonal, and 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 provides 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 obtained have been used to calculate bounds on alpha* in the case of polycrystals belonging to symmetry classes listed above, and the results obtained are found to compare favorably with observations. (C) 1995 American Institute of Physics.