| The major obstacle in applications of ferroelectric ceramics is the so-called electric fatigue which refers to deterioration of piezoelectric properties under cyclic electric loading conditions. Experimental observations indicate that fatigued ferroelectric specimens usually contain a large number of scattered microcracks, and hence suggest that microcracking may be the primary cause of electric fatigue. To study the correlation between microcracking and deterioration of macroscopic properties of polycrystalline ferroelectric ceramics, a computational analysis is carried out on the dependence of macroscopic properties upon microstructural evolution.; To model the microstructural evolution, the principal activity of ferroelectric ceramics under cyclic loading, an evolution law is proposed to govern the rate at which microstructure progresses under the combined influence of local stress and electric fields. The modeled poling, the process for obtaining polarized materials, suggests that there exists a critical value for the poling field strength above which materials do not gain additional electromechanical coupling but they are subjected to a greater risk of electric breakdown. Under mechanical loading, domain switching takes the responsibility for the strain/stress nonlinearity and depolarization. The modeled responses of specimen subjected to uniaxial compression are presented and the results are compared with some experimental observations. The hysteretic responses of dielectric displacement and deformation to applied cyclic electric field, characteristics of ferroelectric ceramics, are simulated. Moreover, the correlation between the hysteretic behavior and the microstructural evolution is revealed. The simulation also indicates that the material quality, such as porosity, and the external loading conditions, have significant effects on the material behavior, and it provides guidance to consider these effects in practical applications.; To model the deterioration of macroscopic properties due to microcracking, a criterion that governs the generation of microcracks at tri-grain junctions due to cyclic loading is supplemented. In this criterion, microcracking is attributed to the stress concentrations at tri-grain junctions. The results indicate that microcracking is associated with microstructural evolution under cyclic loading conditions, and it indeed leads to the commonly-observed fatigue phenomenon. |
