ABSTRACT
The introduction of multiphase models with a second elastic constant further defmed the upper and lower bounds. This development occurred in solid state mechanics and was first applied to metals and compound materials [5-7]. The results were obtained using the variational principle of linear elastic theory for composite sphere geometry [6]. The Hashin-Shtrikman limits (H-S) were also deduced for multi phase models widi random geometry [7]. While the description of the effective bulk modulus is possible with simple energy methods, it is more difFicult for the effective shear modulus. Christensen und Lo solved the problem for different geometries with results within the H-S-limits [8,9].
