These applications require the largest possible strain and force. This results in their operation at high stress and electric fields, in which the materials show strong nonlinearity and hysteresis. Large electric field and stress concentrations near the flaws and the end of electrodes are a main cause of failures many ferroelectric actuators.
Fracture mechanics is used to understand and model such failures.
Understanding and modeling the nonlinear constitutive behavior of piezoelectric materials are an important first step toward improving the design and performance of actuators. Multiaxial experiments were performed to understand the material behavior under combined electric and mechanical loading. Yield surfaces of ferroelectric materials were determined experimentally. A micromechanics constitutive model was developed to simulate the nonlinearity and hysteresis of polycrystalline ceramics by volume averaging the behavior of single crystal grains. The constitutive law includes the effects of ferroelectric and ferroelastic polarization reorientation.