On new phase intermediate layers in nanocomposites as a source of increasing the elastic moduli

We study an opportunity to increase elastic moduli of a nanocomposite due to stress-induced phase transformations which lead to the formation of intermediate new phase layers around nanoparticles. These layers enlarge the effective size of the particles which from now become inclusions made up of kernels (the initial nanoparticles) enclosed by new phase layers shells. Increasing the volume fraction of the inclusions can change the effective elastic moduli of the composite much more than one could expect in a case of the composite with a small volume fraction of initial nanoparticles. As an example we consider an isotropic composite with spherical particles under hydrostatic loading. We begin with considering the new phase formation around an isolated inclusion including the interface stability analysis. We show that stable two-phase states are impossible if both elastic moduli of the matrix increase due to phase transition and possible if the bulk modulus increases and the shear module decreases. Then, basing on a self-consistent approach, we describe the new phase formation around spatially distributed particles and study how external strains effects the new phase areas growth. Finally we demonstrate that the new phase layers formation can lead to increasing the effective bulk modulus of the composite.