Micromechanical model of polycrystalline ferroelectrelastic material defects

Constitutive equations are proposed that describe the nonlinear behavior of a polycrystalline ferroelectroelastic material and taking into account the dissipative nature of the movement of domain walls, the presence of point defects, and their effect on switching processes in the temperature range not accompanied by phase transitions. The method of two-level homogenization is used to describe the behavior of a polycrystalline ferroelectroelastic material at the macro level. Accounting for defects in the micromechanical model of ferroelectroelastic materials has significantly improved the predictive ability of the model under multiaxial loading. Comparison of the results of computations with experimental data on dielectric hysteresis curves and switching surfaces under nonproportional loading of polycrystalline piezoelectric ceramics PZT-4D, PZT-5H and BaTiO$_3$ shows that the proposed model has good prediction accuracy.