Multiaxial constitutive behavior of ferroelectric materials

Multiaxial ferroelectric/ferroelastic constitutive laws governing the behavior of ceramic lead zirconate titanate (PZT) are needed for numerical calculations of stress and electric field in the vicinity of field concentrators such as cracks, inhomogeneities, and partial electrodes. Multiaxial constitutive behavior was measured using tubular specimens, both poled and unpoled. The specimens were subjected to simultaneous axial load internal pressure, and external pressure. Deformation was measured using strain gages. The results were used to map out a "yield" (ferroelastic polarization reorientation threshold or switching) surface. The composition used 8/65/35 PLZT, was found to obey a Tresca criterion when in the unpoled state. The switching surface was found to be a function of the polarization state. Kinematic and isotropic hardening appear to be good candidates for describing subsequent switching surfaces.