Effective-medium theory for infinite-contrast, 2D-periodic, linear   composites with strongly anisotropic matrix behavior: dilute limit and   cross-over behavior
  The overall behavior of a 2D lattice of voids embedded in an anisotropic matrix is investigated in the limit of vanishing porosity f. An effective-medium model (of the Hashin-Shtrikman type) which accounts for elastic interactions between neighboring voids, is compared to Fast Fourier Transform numerical solutions and, in the limits of infinite anisotropy, to exact results. A cross-over between regular and singular dilute regimes is found, driven by a characteristic length which depends on f and on the anisotropy strength. The singular regime, where the leading dilute correction to the elastic moduli is an O(f^{1/2}), is related to strain localization and to change in character - from elliptic to hyperbolic - of the governing equations. 
Francois Willot, Yves-Patrick Pellegrini, Martin I. Idiart, Pedro   Ponte Castaneda