In the present work, we study the effective fracture toughness of ferroelectrics by taking the microscopic as well as the macroscopic level into account. On the macroscopic length scale, we apply an extended theory of stresses at interfaces in dielectric solids. Further, on the microscopic length scale, nonlinear effects are introduced by applying the small-scale switching approximation, that is, the effects are limited to a small region around the crack tip. Finally, we discuss the effective fracture toughness and crack resistance curves for different loading and poling conditions. In contrast to previous approaches, the analysis is done considering the full anisotropy and electromechanical coupling of the material by using piezoelectric weight functions. Thus, the presented model also takes the inverse switching (180°) into account yielding a contribution to both the stress and the electric displacement intensity factors.
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