Effect of Different Support Materials of Smart Sensor Layers on Lamb Waves Propagation

Kurzfassung

Lamb wave based Structural health monitoring (SHM techniques are widely used for real-time damage detection in critical structural components. For Lamb-based SHM, piezoelectric lead zirconate titanate (PZT) transducers are employed for actuation and sensing. The choice to use a SHM system as a maintenance approach for a structure is directly associated with the incremental cost and reliability of the system in comparison to traditional schedule-based maintenance. The installed sensors are typically unprotected from the aircraft's operational environment, rendering PZT sensor failure a significant risk. The malfunction of any PZT sensor will diminish diagnostic reliability, leading to missed detections and false alarms, thereby undermining system performance. So, it is necessary that the sensors withstand the operating environmental conditions and that there is a provision for easy replacement of the faulty transducer. In recent years, inkjet printing, particularly drop-on-demand (DoD) inkjet printing, has been utilized as an efficient and economical method for the manufacturing of electronic devices. Based on current technologies industry-scale transducer layers are available, like the integrated SHM layer and the SMART Layer. Studies have shown that the insulating coating of wires is mainly based on polymers. The polyamide, known as Kapton, was found suitable as a coating material because of its good bonding properties to composites and its good electrical insulation. Recent studies have also shown the use of polyethylene terephthalate foil (PET foil), thermoplastic polyurethane foil (TPU foil), as support materials for flexible sensors. However, there is no study available on the suitability of these materials as support materials for piezoelectric-based SHM systems for ultrasonic-based damage detection The present work aims to study the suitability of polyethylene terephthalate (PET) foil, thermoplastic polyurethane (TPU) foil, and Polypropylene (PP) laminated nonwoven fabric as support materials for PZT-based flexible sensors for SHM applications. Specifically, the aim is to find the effect of these materials on Lamb wave propagation in composite structures. Kapton is also used as one support material for comparison. The experimental setup consists of five glass fiber-reinforced polymers (GFRP). Each plate was surface mounted with four DuraAct-made piezoelectric transducers. Experimental studies are conducted at room temperature (20 °C), low temperature (-20 °C), and high-temperature (60 °C) environments to simulate actual operating environments of the SHM system. Lamb wave generation propagation and sensing experiments are conducted without the support materials and also after pasting the support materials. The wave field analysis is also conducted using the plate without support material and with support material. The study reveals that the use of TPU foil and PP laminated nonwoven fabric as support material has a very low effect on the Lamb wave propagation in the structure in comparison to the Kapton and PET foil. The presence of Kapton and PET also significantly influences the Lamb wave propagation in varying thermal environments. This makes TPU foil, and PP laminated nonwoven fabric two suitable candidates as support materials for flexible PZT-based sensor systems for Lamb wave-based SHM applications.