Experimental and numerical investigation of the bonding conditions of piezoelectric sensors under high compressive strains on structures

In the past two decades, thin lead zirconate titanate (PZT) sensors have been widely used in the electro-mechanical impedance (EMI) technique for sensing applications, particularly for monitoring civil structures. They are typically surface bonded using an industrial adhesive to the monitored structure. The bond between a PZT sensor and structure must be sufficiently strong to transmit the response of the structure to the sensor. In this study, acrylic cubes bonded with PZT patches are subjected to high compressive strains above 2000 με to develop a better understanding of bonding conditions when structures undergo such high strains. Acrylic can undergo such high strains without developing fissures or cracks. Thus, the recorded EMI response only reflects changes in the bonding condition due to the development of strains. The experiments are also numerically supplemented by simulating various debonding conditions. At higher strains, it was observed that the admittance signatures tend to behave similarly to a freely vibrating PZT patch, indicating debonding around the periphery. Even after the complete unloading of the structure, the signatures did not return to their initial state, indicating a permanent partial debonding. The strains developed on a loaded structure are not uniform and can be localized due to structural imperfections, resulting in higher strains in the region where a sensor is bonded. The insights from this study will aid in expanding the scope of the application of PZT sensors for monitoring civil structures through better comprehension of the PZT-structure bond under high compressive strains.