Toughness variation of ferroelectrics by polarization switch under non-uniform electric field

Low fracture toughness of ferroelectric ceramics calls for a reliability concern in the development of smart structures. For ferroelectrics under mechanical and electrical loadings, the intensified stress and electric fields in the vicinity of a crack-like flaw lead to domain reorientation. The switched domains induce incompatible strain near the flaw and consequently change the apparent fracture toughness. The present paper investigates toughness variation by small scale polarization switching under non-uniform electric and stress fields. A two-term near lip electric field is obtained by analyzing a permeable elliptical flaw in a ferroelectric solid. Analytical solution for the shielding stress intensity factor is derived for the ideal situation of mono-domain ferroelectrics. The result is generated by a Reuss-type assembly to the poly-domain ferroelectrics. The predictions based on the present model explain the conflicting experimental data on the toughness variations with respect to the applied electric field. (C) 1997 Acta Metallurgica Inc.