MICROSTRUCTURES MINIMIZING THE ENERGY OF A 2-PHASE ELASTIC COMPOSITE IN 2 SPACE DIMENSIONS .1. THE CONFOCAL ELLIPSE CONSTRUCTION

For modeling coherent phase transformations and for applications to structural optimization, it is of interest to identify microstructures with minimal energy or maximal stiffness. We present a new and appealingly simple class of extremal microstructures, which we call the confocal ellipse construction, for the case of a two-dimensional elastic composite made from two isotropic elastic materials. When the macroscopic stress and strain are isotropic, our construction reduces to the well-known ''coated sphere'' microstructure.