Measuring fracture toughness of piezoceramics by vickers indentation under the influence of electric fields

Abstract

The Vickers indentation technique was used to determine the apparent fracture toughness of PZT-4 piezoceramic under the influence of electric fields. The toughness was measured in terms of the mechanical strain energy release rate. Using the analytical mechanical strain energy release rate for an infinite piezoelectric medium with a center crack and far field in-plane mechanical and electrical loadings, the mechanical strain energy release rate was obtained for Vickers indentation. The effect of the electric field was included. The proposed formula was evaluated with the experimental results. It was found that the fracture toughness depended on the indentation force. Vickers indentation tests were also performed on depoled PZT-4 specimens; these test results indicated that the fracture toughness of depoled PZT-4 was also dependent on the indentation force. To eliminate the indentation force dependence, a modified stress intensity formula based on Vickers indentation was proposed.

Phase-Field Modeling of Fracture in Ferroelectric Materials

“…The Vickers indentation technique is commonly used in determining this anisotropy [75,89,101,112,116,121]. These experimental observations show that the cracking along the poling direction of the material has a shorter length and consequently higher fracture toughness, and that normal to the poling direction has a longer length and lower fracture toughness.…”

“…Other tests have indicated an opposite phenomenon, where their results show that a positive applied electric field inhibits crack propagation, whereas crack propagation is enhanced under a negative applied electric field [50,95,106,121]. On the other hand, experiments do not show a clear shielding or weakening effect of the microstructure on insulating cracks oriented parallel to the poling and electric field direction [112,116]. This behavior is not expected since experiments without electric field indicate that in this configuration a pronounced domain switching zone is developed during crack growth [100].…”

“…• Radial cracks perpendicular to the poling direction of the material propagate faster than parallel ones [2,75,89,101,112,116,121].…”

“…However, there are a number of contradictions and inconsistencies between reported results. Experiments on insulating cracks have shown that a positive electric field promotes crack extension perpendicular to the poling axis of the material, whereas a negative electric field retards it [75,101,112,116]. Other tests have indicated an opposite phenomenon, where their results show that a positive applied electric field inhibits crack propagation, whereas crack propagation is enhanced under a negative applied electric field [50,95,106,121].…”

Electroelastic intensification and domain switching near a plane strain crack in a rectangular piezoelectric material

“…In the experimental data [Sun and Park 2000], crack length deviated from the linear function of the electric field for the case of a larger load, especially for negative electric fields. By including the polarization switching effect of the energy release rate, the observed nonlinear dependence of piezoelectric crack behavior on the electric field is explained.…”