The proofs of the optimal bounds for mixtures of two anisotropic conducting materials in two dimensions

Abstract We provide a complete proof of the result announced 20 years ago in Francfort and Murat [Francfort, G.A., Murat, F., 1987. Optimal bounds for conduction in two-dimensional, two-phase, anisotropic media. In: Knops, R.J., Lacey, A.A., (Eds.), Nonclassical Continuum Mechanics (Durham, 1986), London Mathematical Society Lecture Note Series, vol. 122, Cambridge University Press, Cambridge, pp. 197–212], namely the characterization in two dimensions of the set of the effective conductivities obtained by mixing two anisotropic conducting materials with arbitrary orientation. We also provide a complete proof of the characterization (also already announced in Francfort and Murat (1987)) of the sets of conducting materials with arbitrary orientation which are stable under H -convergence in two dimensions.