Abstract
Structural Health Monitoring based on Lamb waves, a type of ultrasonic guided waves, is a promising method for in-service inspection of composite structures. In this study, mode selective actuators are developed to excite a particular Lamb wave mode in quasi-isotropic CFRP (carbon fibre-reinforced polymer) plates. Different manufacturing technologies based on monolithic piezoceramics and piezocomposites are described. The actuators are based on interdigital transducer design in order to control the frequency as well as the wavelength of the desired mode within the excitation. To determine the wavelength of the desired Lamb wave mode, experimental dispersion diagrams of the CFRP plates are measured using air-coupled ultrasonic scanning technique. The dispersion diagrams show the A 0 and S 0 mode in a frequency range of 25–400 kHz. A mode selective actuator is designed to amplify the A 0 mode and to attenuate the S 0 mode at 40 kHz. Within experimental tests the actuator and circular piezoceramic sensors are applied on a CFRP plate in order to determine the mode selectivity. These tests are accompanied by 2D finite element simulations. On the basis of simulations and experimental test the influence of different parameters such as number and width of electrode segments, excitation signals and apodization is investigated. The results show that a mode selectivity of the A 0 mode in CFRP plates can be achieved by the designed actuator.
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Acknowledgments
The DLR-Institute of Composite Structures and Adaptive Systems performs basic research on Structural Health Monitoring within a project of the German Research Foundation (DFG) in cooperation with several partners of the Helmut Schmidt University and the Otto-von-Guericke-University Magdeburg. The authors would like to thank the German Research Foundation as well as all project partners for their support.
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Schmidt, D., Sinapius, M. & Wierach, P. Design of mode selective actuators for Lamb wave excitation in composite plates. CEAS Aeronaut J 4, 105–112 (2013). https://doi.org/10.1007/s13272-012-0059-3
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DOI: https://doi.org/10.1007/s13272-012-0059-3