A FULLY COUPLED CONSTITUTIVE MODEL FOR ELECTROSTRICTIVE CERAMIC MATERIALS

A three-dimensional, electromechanical constitutive law has been formu lated for electrostrictive ceramic materials. This fully coupled, phen omenological model relates the key state variables of stress, strain, electric field, polarization and temperature in a set of compact nonli near equations. The direct and converse electrostrictive effects are m odeled by assuming that the electrically induced strain depends on sec ond-order polarization terms. In addition, a simple empirical relation ship for the dielectric behavior is used to model the saturation of th e induced polarization with increasing electric field. Unlike previous electrostrictive constitutive laws based on polynomial expansions, th is constitutive law depends on a manageable number of material constan ts. As an example, material constants for the model were determined fr om induced strain and dielectic data for a relaxor-ferroelectric based on lead magnesium niobate, Pb(Mg1/3Nb2/3)O-3-PbTiO3-BaTiO3 (PMN-PT-BT ). Finally, predictions of the material's mechanical behavior under co nstant electric field and its electrical behavior under constant appli ed stress are made.