Toughening of conducting cracks due to domain switching Original Research Article

Recent investigations [Heyer et al., Acta mater. 46 (1998) 6615] of conducting cracks under combined electrical and mechanical loading in piezoelectric ceramics revealed that the fracture load (KI) changes with applied electric field (KE). The experimental observations contradict theoretical predictions based on linear piezoelectricity and strip-saturation models. In this paper, interaction between a semi-infinite conducting crack and switching induced strains and polarizations is studied to examine the above discrepancy. New fundamental solutions for the electroelastic field intensity factors induced by transformation strains and polarizations are derived and used to develop a model for variation of fracture toughness due to domain switching. A work energy based criterion for domain switching and a Reuss-type approximation for poly-domain piezoelectrics reported previously are used in the modeling. The influence of electromechanical loading and poling direction on the switching-induced stress intensity factors (toughness variation) is studied for PZT-5H. Under combined electrical and mechanical loading, a positive electric field is found to increase apparent fracture toughness of a crack parallel to the poling direction, while a negative one tends to reduce it. This prediction is consistent with experimental observations.