Advancing measurement of zero-group-velocity Lamb waves using PVDF-TrFE transducers: first data and application to in situ health monitoring of multilayer bonded structures

Abstract

Driven by the rapid advancement in manufacturing technologies, engineering structures with complex geometries are increasingly applied in various industries, posing challenges to the applicability and adaptability of existing structural health monitoring methods based on guided ultrasonic waves. To fulfill the characterization of defects in complex structures, a novel approach featuring a conjunction of zero-group-velocity (ZGV) Lamb waves and polarized poly(vinylidenefluoride-co-trifluoroethylene) (PVDF-TrFE) transducers is proposed. In this approach, the PVDF-TrFE solvent is deposited and in situ polarized on the structure surface to form thin and flexible coatings, with which the ZGV waves can be excited efficiently and measured reliably. On this basis, the defect can be characterized by investigating the defect-induced alteration in ZGV wave features. In experimental validations, disbond defects in multilayer bonded structures are evaluated using the ZGV waves measured with fabricated PVDF-TrFE transducers. For the first time, the ZGV waves are measured in a contact and in situ manner. Compared with conventional noncontact measurement of ZGV waves, the proposed approach features a remarkably improved reliability, convenience for narrowband excitation, immunity to measurement uncertainty and capability of in situ monitoring. The proposed approach can advance the ZGV wave-based methods toward the in situ health monitoring and enable the defect evaluation in emerging complex structures.

Distinctive trembling features following resonance peaks at zero group velocity frequencies in harmonic analysis

“…Enormous endeavors have also been devoted to the extraction techniques of ZGV modes, particularly in versatile materials and complicated structures. The existence of ZGV modes has been validated in thin plates and membranes [6,[23][24][25][26][27], thin films [14], isotropic [15]/hollow cylinders [28], rigid/soft strips [29], concrete materials [12], and multi-layered structures [10,30]. Furthermore, Li et al validated the presence of ZGV features in a welded joint subjected to a force source [31].…”

“…Considering the peculiarity of ZGV modes, the actuation, measurement, and extraction of ZGV modes are therefore of great significance. Various sensors have been utilized for the excitation and measurement of ZGV resonances, classified as contact and noncontact approaches, and encompassing PVDF-based transducers [10], EMAT [11], accelerometer/microphone [12], air-coupled transducers [13], laser interferometers [9], interdigital transducer (IDT) [14], and laser doppler vibrometers [15]. To name a few, Zhu et al exploited piezoelectrical wafer active sensors (PWAS) to selectively actuate ZGV resonances and utilized Physical Acoustics NANO-30 sensor to measure temporal vibration signals at different locations [7].…”