Interfacial fracture of piezoelectric multilayer actuators under mechanical and electrical loading

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 Γ.