Fracture of Piezoelectric Materials

Abstract

The present work studies, theoretically and experimentally, the fracture behavior of piezoelectric ceramics. For an electrically insulating crack, the ratio of β α / plays an important role in the energy release rate, where α is the ratio of the minor semi-axis, b, to the major semi-axis, a, of the ellipse, and β is the ratio of the dielectric constant of the cavity to the effective dielectric constant of the material. There are three limiting values in the energy release rate, respectively corresponding to 0 / → β α for an electrically permeable crack, → β α / a finite nonzero value for general cases and ∞ → β α / for an electrically impermeable crack. For an electrically conductive crack, the applied electric field parallel to the crack drives the crack to propagate. When electric yield occurs at a crack tip, the global energy release rate is the same as that derived from linear fracture mechanics, while the local energy release rate shows a linear relationship between the fracture toughness and the applied electric field. The experimental results illustrate that for PZT-841 and PZT-4 ceramics, the degree of scattering of measured data was considerably enhanced by an applied electric field. Either a positive or a negative electric field reduced the fracture toughness. The experimental results also confirmed that there exist mechanicaland electrical-fracture toughness for PZT-4 ceramics and both are material properties. The mechanicallyand electricallycritical energy release rates are, respectively, 8.7(±1.1) and 223.7(±45.5) N/m.