Experimental study of fatigue and fracture of piezoceramics

In this presentation, the experimental study of fatigue and fracture of piezoelectric ceramics is introduced. The work consists of two parts, i.e., (1) Study of anisotropic fracture behaviour of ferroelectric ceramics subject to combined electromechanical loading by using a moiré interferometry technique; (2) Fatigue crack growth in ferroelectric ceramics driven by cyclic electric field. The fringe analysis gives insight into the level of toughening related to domain switching. The deformation fields near the crack tip, the crack-end open displacement (CEOD), and the critical fracture load in three-point bending experiments were measured. By analysing the moiré fringe images it is found that strain decreases faster than values predicted by the finite element analysis as the distance away from the crack tip increases. The results show that the strain not only concentrates at the crack tip but also significantly appears along the crack wake due to the in-plane 90° domain switching. The experimental results show that there are two distinct fatigue mechanisms. That is, under low electric loading, the emergence and growth of micro-cracks is the major fatigue mechanism, while under a high electric field, the propagation of the main crack is dominant. A steady crack growth occurs after E=1.0E_c. Theoretical analyses are made to predict the cracking threshold. Empirical relations are obtained to describe and predict the crack growth rate in the electric-field-induced fatigue.