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Field singularities of collinear and collinear periodic interface cracks between an electrode and a piezoelectric matrix are studied in terms of the Stroh formalism for mixed boundary conditions. In contrast to the relevant work done previously on this subject, the problem is solved based on the assumption that the upper and lower planes embedding the electrode consist of two arbitrary piezoelectric materials, and the cracks are assumed to be permeable. The problem is reduced to an interfacial crack problem equivalent to that in purely elastic media. Explicit expressions are presented for the complex potentials and field intensity factors. All the field variables exhibit oscillatory singularities, and their intensities are dependent on the material properties and the applied mechanical loads, but not on the applied electric loads.

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The fracture behaviour of metal-piezoceramic interfaces under mechanical and electrical loading is examined by four point bending using commercial multilayer actuators. The experiments are performed under stable crack growth in a custom made very stiff testing machine. Besides mechanical loading, a constant electric field was methodically switched on in longitudinal specimen direction. Both poled and unpoled actuators were tested. The crack morphology and the fracture toughness depend on the type of the metal-ceramic interfaces. Assuming different electrical crack boundary conditions of a permeable and an impermeable crack, the field intensity factors K ic , with i = 1, 2, 3, and energy release rates G c (K ic ) at the measured critical loads are evaluated with linear-piezoelectric finite element calculations. Inside the bounds of the electrically induced mixed-mode angles, the permeable crack boundary condition yields a constant interface toughness .