Cracks in ferroelectric ceramics - Kelvin-Force-Microscopy and 4-point bending tests

Project manager:Prof. Dr. rer. nat. Gerold A. Schneider
Project worker:Dipl.-Ing. Andrea Engert, Dr. rer. nat. Hans Jelitto
Supported by:Deutsche Forschungsgemeinschaft (DFG)
Collaboration:Technische Universität Dresden,
Institut für Festkörpermechanik,
Prof. H. Balke, Dipl.-Ing. P. Neumeister


In ferroelectric ceramics crack nucleation and crack propagation are characterized by critical stresses as well as crack driving and crack resistance forces. All of these factors are highly dependent on the applied boundary conditions and the load history. In this work the electric boundary conditions at the crack surface, the effect of charges, polarization and the changes in domain structure on the fracture toughness are of primary interest.

With the help of the Kelvin-Force-Microscopy (KFM) the potential drop across a crack is measured for different applied electric fields (figure 1) and the surface charge density at the crack surface is calculated with the help of the crack opening displacement (COD) and the potential drop across the crack (figure 2).

Furthermore a time dependence of the charge distribution is analysed when the applied electric field is changed (figure 3).

4 Point bending tests with different electromechanical loading rates, AC, unipolar and DC voltages (figure 4) are performed in order to investigate the influence of the applied electric field on the fracture toughness (figure 5).