Switch-toughening of Ferroelectrics Subjected to Electric Fields

Electric tields can mtluence the fracture toughness offerroelectrics. For example, poled ferroelectrrcs cxhtbit fracture toughness anisotropy : the material is tougher for a crack parallel to the poling direction but less tough for a crack perpendicular to it. When an electric field is applied to a poled sample. a positive field reduces its fracture toughness but a negative field enhances it. Previous investigations attribute these phenomena to polarization switching. This paper proposes a model of stress-assisted 90 polarizitron switching to quantify the toughening process. Small scale switching and uniform electric fields are assumed. An analytical solution is presented for a mono-domain ferroelectric crystal undergoing a confined polarization switch. This solution and the domain orientation pattern enable us to estimate the fracture resistance against the steady state crack growth m ferroelectrics by a Reuss-type multiple-domain assembly. 4 dimensionless group of material parameters and an electric field f’unction emerge. and form the key ingredients of switch-toughening. The model is used to delineate several observations, includrng: polinginduced anisotropy of the fracture toughness, asymmetric vat-ration of the fracture toughness under posrtivc and negative electric fields of a poled specimen ; upside-down butterfly loop for the fracture toughness response under cyclic electric loading. (‘1 1998 Elscvier Science Ltd. All rights reserved.