Design against fracture of piezoelectric layers used within smart systems

The wide use of piezoelectric materials in many smart systems motivates the current need of predicting very effectively their reliability. A key issue of design of the piezoceramic layers is preventing some damage like fracture, fatigue and creep. Prediction of crack propagation through a piezoelectric layer while its active functions are exploited is rather difficult. Analytical methods already proposed in the literature often fail when either geometry is more complicated than a rectangular patch or structural behaviour becomes nonlinear because of a large vibration amplitude, typical, for instance, of the vibration energy harvesters. A research activity was therefore aimed at assessing a reliable numerical tool to combine the prediction of crack propagation within the piezoelectric layer through the Finite Element Method and the analysis of the electromechanical coupling between strain and voltage. The crack behaviour inside the smart material is described by calculating the so-called Stress Intensity Factor (SIF), the J-integral and the crack path, but in this case local effects induced by the piezoelectric phenomenon are included. The ABAQUS code was used to investigate both the fracture mechanics and the piezoelectric phenomenon, by means of the ISIGHT tool which connected the two environments of the code which perform separately those analyses. This approach allowed detecting the reaction applied by the electromechanical coupling to the crack propagation at its tip, in operating conditions. The above mentioned tools and results allowed investigating some particular effects of piezoelectric phenomenon on the smart structure behaviour in service