A phase field model is used to study the domain structure in the surrounding of a the crack tip in thin layers (films,coatings) after poling.The finite element simulations focus on the influence of parameters like film thickness,electrode stiffiness and grain boundaries.Furthermore,the effect of different boundary conditions is investigated.In this context,configurational forces are used to determine the crack extension force.It is shown that the electrode and the substrate may dramatically reduce switching and that this behavior can be modeled by an appropriate Robin-type boundary condition.