Multiaxial constitutive behavior of ferroelectric materials

Multiaxial ferroelectric/ferroelastic constitutive laws governing the behav ior of ceramic lead zirconate titanate (PZT) are needed for numerical calcu lations of stress and electric field in the vicinity of field concentrators such as cracks, inhomogeneities, and partial electrodes. Multiaxial consti tutive behavior was measured using tubular specimens, both poled and unpole d. The specimens were subjected to simultaneous axial load internal pressur e, and external pressure. Deformation was measured using strain gages. The results were used to map out a "yield" (ferroelastic polarization reorienta tion threshold or switching) surface. The composition used 8/65/35 PLZT, wa s 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 an d isotropic hardening appear to be good candidates for describing subsequen t switching surfaces.