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Evaluation of electromechanical characteristics for screen printed piezoelectric sensor-based Pu/PZT composite

This paper reports on a novel measurement method to characterize piezoelectric thin layer (~ 20 μm) through a four-point bending (4PB) setup. Polymer-based piezoelectric composite is directly screen printed onto the surface of host structure, which is assimilated to an instrumented steel substrate. Because of electromechanical coupling properties, a voltage signal can be generated through the piezoelectric sensor when subjected to mechanical strain in its film plane. As the typically sensor layer is very thin in comparison to the underlying substrate, the mechanical properties of the whole system are mainly determined by the characteristics of the steel-type material. Furthermore, the piezoelectric layer properties strongly depend on underlying substrate, electrodes, and the processing route of the layered sensor structure. Therefore, the method developed here enables to reliably extract characteristics such as the effective piezoelectric behavior of the thin composite. In combination with a strain gage coated onto the back side of the substrate, the developed setup allows the determination of the effective piezoelectric sensitivity. The homogeneous strain distribution in the sensing layer is verified by finite element simulations. Furthermore, analytical model is investigated to predict the mechanical behavior of the 4PB structure. The results demonstrate that the developed sensing setup is capable to provide a direct strain/stress measurement instead of traditional techniques through interpolation, and thus offers an efficient method for on-line and in situ structural health monitoring of bearing.