A Prestress Measurement Circuit for Piezoceramic Stack Transducers

Recently, new multifunctional fasteners called `smart fasteners´ have been proposed for structural health monitoring applications. These devices can be fabricated by modifying the design of ordinary fasteners such that they have a piezoceramic stack transducer embedded in their body. Like ordinary fasteners, smart fasteners can be installed simply by tightening the fastener with sufficient torque to create a tensile load in the fastener, which in turn applies prestress to the piezoceramic transducer. However, in order to achieve repeatable actuation and sensing performances, consistent prestress should be applied to each embedded piezoceramic transducer to ensure minimal device-by-device variation. In this research, a simple electronic circuit was developed for the measurement of the prestress in the piezoceramic stack transducer. For this purpose, mathematical models for the piezoceramic stack transducer and the measurement circuit were derived and the relationship between the applied stress and the circuit output voltage was established. This relationship was experimentally verified with various measurement data. Finally, the measurement circuit was calibrated with a load cell so that the output voltage can be used for a correct prestress reading. Compared to a gauged torque wrench, the proposed circuit offers a more accurate and cost effective way to measure prestress of piezoelectric stack transducers.