Crack growth in piezoelectric materials under combined mechanical and electrical loadings

An experimental and analytical investigation of crack propagation in piezoelectric ceramics subjected to both mechanical and electrical loadings is performed. The crack propagation in a piezoelectric lead zirconium titanate (PZT) material under simultaneous mechanical and electrical loads is experimentally studied using the Vickers indentation technique. The results have demonstrated that appropriate applications of electric fields can inhibit or enhance crack propagation in piezoelectric materials. Cracks introduced by indentation are observed to propagate less under a positive applied electric field in which the polarity of the field is the same as that for poling whereas the crack propagation is enhanced under a negative applied electric field. Such an effect is observed to be more profound with increasing electric field strength and decreasing mechanical loading. A finite element model is developed to study the stress distributions at the crack tip of piezoelectric ceramics because of the mechanical and/or electrical loads. It is shown that the stress intensity factor at the crack tip is increased with an increase in the electrical to mechanical load ratio for a negative applied electric field while compressive stresses are developed at the crack tip for a positive applied electric field which are in agreement with the experimental findings. A mechanism for the crack propagation behavior of the piezoelectric material under applied electric fields is proposed.