Distinguishing the Degradation of the Interdigital Piezoelectric Fibre Transducers From Structural Damage in Multifunctional Composites

The next-generation design of structural components involves combining multiple functions. The goal of such Multi-functional structures (MFS) is to incorporate various tasks and functions such as structural, electrical and thermal features within a structural housing. The performance and behaviour characteristics of the multi-functional structures can be affected by degradation of any of the sub-components. This can have consequences on the safety, cost, and operational capability. Therefore, the timely and accurate detection, characterization and monitoring of the degradation in these sub-components are major concerns in the operational environment. This calls for Structural Health Monitoring (SHM) as a possible method to improve the safety and reliability of structures and thereby reduce their operational cost. As the application of SHM systems to monitor the status of the MFS increase, it will be increasingly important to determine the durability, reliability, and reparability of the components of SHM system such as sensors. The sensors themselves must be reliable enough so that they do not require replacement at intervals less than the economic lifetime of the structures and components they are monitoring. This is especially important when the deleterious structural changes in the sensor occurs without any discernible change in the structure being monitored In the present work, an assessment is carried out to quantify the degradation in the electric and electromechanical characteristics of polymer composite PZT sensors, under fatigue loading. Changes in the electrical properties of these sensors such as capacitance and inductance have been measured. The strain measurements of the sensor have also been compared to the theoretically calculated strain. The results show that the delineation of structural damage from sensor degradation is possible by monitoring the changes in the key electrical properties of the sensor components such as electrodes and PZT fibers as well as the comparison of experimentally measured and theoretically calculated strain values.