Dynamic fatigue of cracked piezoelectric ceramics under electromechanical loading: three-point bending test and finite element analysis

Abstract

This paper studies the dynamic fatigue or slow crack growth in piezoelectric ceramics under electromechanical loading by a combined numerical-experimental approach. Constant load-rate testing was conducted in three-point flexure using the single-edge precracked-beam specimens under zero and positive electric fields, and the effects of electric field and loading-rate on the fracture load and crack propagation were examined. A finite element analysis was also employed to calculate the energy release rate for the permeable, impermeable and open crack models, and the effect of electric field on the energy release rate was discussed. Crack propagation velocity versus energy release rate curves at various loading-rate were then estimated based on the finite element analysis using measured data. Piezoelectric ceramics of the lead zirconate titanate (PZT) class have been used for a number of years as sensors and actuators. The high mechanical stresses and intense electric fields in PZT ceramics can induce cracking that can lead to premature failure of the piezoelectric devices. The properties of PZT ceramics are also susceptible to degradation under electromechanical loading. Therefore, an understanding of piezoelectric fracture [Shindo et al. 2003; 2005] and fatigue [Cao and Evans 1994; Lynch et al. 1995] is a key issue for the efficient and reliable design of the piezoelectric devices. Shindo et al. [2007] conducted an experimental and analytical study of the static fatigue behavior of PZT ceramics under electromechanical loading. Narita et al. [2007] also reported experimental and numerical examination of the fatigue crack growth in PZT ceramics under a cyclic mechanical load and a constant electric field. Certain environments may affect formation and extension of cracks over time and at stress levels well below that which causes immediate failure to occur. This process is called dynamic fatigue or slow crack growth. Slow crack growth parameters have been estimated for only a few commercial ceramics and glass, and no one has investigated the resistance of piezoelectric ceramics to slow crack growth and the influence of electric field on the dynamic fatigue behavior. In this study, we report numerical and experimental examination of the dynamic fatigue or slow crack growth in piezoelectric ceramics under electromechanical loading. A crack was created normal to the poling direction. Constant load-rate testing was conducted in three-point flexure under zero and positive electric fields using single-edge precracked-beam method. A finite element analysis was also used to evaluate the energy release rate for the permeable, impermeable and open crack models, and the effect