Modern piezoelectric transducers normally have complicated structures and work under severe loading conditions. Application of an external load in excess of a critical level will cause domain switching in the material and therefore lead to a significant nonlinearity and hysteresis in the polarization and strain response. To develop a constitutive model concerning the large-signal nonlinear behavior of ferroelectric piezoceramics, it is desirable to determine a switching criterion in the multiaxial stress and electric field states.
In this experimental work, "soft" lead zirconate titanate (PZT) specimens in initially unpoled state were subjected to a proportional electromechanical loading, in which a compressive stress and a parallel, proportional electric field were applied simultaneously. By varying the relative proportions of the stress and E-field between tests, a family of nonlinear polarization and strain responses were obtained. An attempt has been made to explain the experimental findings by simultaneously taking into account the contributions of dielectric response, elastic deformation, piezoeffects, and irreversible domain switching. Based on an offset method, switching (domain reorientation threshold) surfaces were mapped out in the biaxial stress and electric field space. Finally, several switching conditions existing in the literature were summarized and compared with the experimental data obtained in this work.