Toughening of conducting cracks due to domain switching

Recent investigations [Heyer ct al., Acta mater. 46 (1998) 6615] of conduct ing cracks under combined electrical and mechanical loading in piezoelectri c ceramics revealed that the fracture load (K-1) changes with applied elect ric field (K-E). The experimental observations contradict theoretical predi ctions based on linear piezoelectricity and strip-saturation models. In thi s paper, interaction between a semi-infinite conducting crack and switching induced strains and polarizations is studied to examine the above discrepa ncy. New fundamental solutions for the electroelastic field intensity facto rs induced by transformation strains and polarizations are derived and used to develop a model for variation of fracture toughness due to domain switc hing. A work energy based criterion for domain switching and a Reuss-type a pproximation for poly-domain piezoelectrics reported previously are used in the modeling. The influence of electromechanical loading and poling direct ion on the switching-induced stress intensity factors (toughness variation) is studied for PZT-SH. Under combined electrical and mechanical loading, a positive electric held is found to increase apparent fracture toughness of a crack parallel to the poling direction, while a negative one tends to re duce it. This prediction is consistent with experimental observations. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights res erved.