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Ultrasonic imaging of contact defects under low frequency loading: application for structural health monitoring of elastic plates

Marina Terzi 1, 2, 3 
2 TPIA - IEMN - Transduction, Propagation et Imagerie Acoustique - IEMN
INSA Hauts-De-France - INSA Institut National des Sciences Appliquées Hauts-de-France, IEMN - Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520
Abstract : In structural health monitoring, acoustic methods without use of a reference intact sample are nowadays of great interest due to variability of environmental and operational conditions. This thesis presents an acoustic reference-free method for detecting and localizing defects in thin plates. The proposed approach is based on pump-probe measurements and a differential signal processing algorithm. The pump-probe scheme here means the simultaneous excitation of low-frequency vibrations and high-frequency acoustic pulses generated by a piezoelectric transducer and recorded by an array of transducers of the same kind. The role of pumping vibrations is in imposing changes to loading conditions for a defect (here a model Hertzian contact i.e. a small ball pressed against the tested plate) while the ultrasonic Lamb wave pulses probe the defect in various loading states. Then a differential signal processing algorithm based on backpropagation of A0 Lamb mode is used to detect and locate the defect. Two detection modes have been studied: the mode requiring the synchronization between the pump and probe signals, and the non-synchronous mode. In the latter case, a correction with the use of ad hoc weight coefficients improves the detection. Further, a parametric study was performed by computing the image contrast as a function of the defect scattering cross-section that allowed us to determine a minimum detection threshold. The application of the method to passive imaging (i.e. using white noise instead of probe pulses) produced encouraging results for the price of increasing the number of receivers. Finally, numerical modeling for the interaction of an ultrasonic wave with a Hertz-Mindlin frictional contact was performed in 2D to compare the model defect (ball pressed against the plate) with a more realistic one (crack).
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https://hal-uphf.archives-ouvertes.fr/tel-03777450
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Submitted on : Wednesday, September 14, 2022 - 4:46:18 PM
Last modification on : Saturday, September 24, 2022 - 4:02:21 AM

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  • HAL Id : tel-03777450, version 1

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Marina Terzi. Ultrasonic imaging of contact defects under low frequency loading: application for structural health monitoring of elastic plates. Acoustics [physics.class-ph]. Université Polytechnique Hauts-de-France; Institut National des Sciences Appliquées Hauts-de-France, 2022. English. ⟨NNT : 2022UPHF0013⟩. ⟨tel-03777450⟩

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