Conducting cracks in ferroelectric ceramics under purely mechanical loading, purely electrical loading and combined case of electrical and mechanical loading are analyzed to investigate the effects of stress and electric fields on fracture behavior. The asymptotic problem of conducting cracks in a mono-domain ferroelectric ceramics as well as in a poly-domain ferroelectric material is considered and the relation between the crack tip stress intensity factor and the applied intensity factor of stress fields and electric field under small scale conditions is investigated. In order to evaluate the crack tip stress intensity factors due to the domain switching, the shape of the domain switching zone attending the crack tip must be determined under various loadings. The evaluation of the shape is carried out based on the nonlinear domain switching model. It is shown that the switching zone boundary and the crack tip stress intensity factors due to the switching depend strongly on the angle of the polarization vector, the ratio of the coercive electric field to the saturated electric field, direction of electrical field, and the ratio of the applied electrical intensity factor to the applied stress intensity factor under combined loding. The electrical fracture toughness of unpoled poly-domain ferroelectrics is examined. Employing a Reuss type approximation, the crack tip stress intensity factors for an unpoled poly-domain material are obtained. The ratio of the critical electrical energy release rate to the critical mechanical energy release rate is obtained. This results can be given to good interpretating for the problem of conductive crack in ferroelectric ceramics.
