Crack propagation in piezoelectric materials under combined mechanical and electrical loadings

A finite element technique is used to study the stress distributions at the crack tip of a piezoelectric ceramic because of the mechanical and/or electrical loads. The stress distributions at the crack tip are found to be in conformity with those predicted theoretically by Sosa and Pak. For combined mechanical and electrical loads, the stress intensity factor at the crack tip is observed to increase with an increase in the electrical to mechanical load ratio for a negative applied electric field (electric field opposite to the direction of poling) which is in agreement with the experimental findings of Wang and Singh. For the positively applied electric field, compressive stresses are found to develop around the crack tip for high electrical to mechanical load ratios. For combined mechanical and electrical loads, the stress distributions at the crack tip under applied stress is found to be significantly different from those under applied strain. It is shown that a negative applied electric field with a tensile strain perpendicular to the crack surface increases the crack propagation.