In this paper results of the damage assessment of composite panel using the guided wave propagation method are presented. Two approaches of elastic wave generation are investigated: (i) contact, piezoceramic transducer (PZT)-based and (ii) non-contact, air-coupled transducer (ACT)-based. Elastic wave sensing is based on scanning laser Doppler vibrometry (SLDV). Both methods of elastic wave generation are compared based on an analysis of elastic wave propagation and damage localization results. For this purpose wave irregularity mapping (WIM) algorithm was utilized. In this research square panels made of fibre reinforced polymer are investigated. Authors investigate artificial damage in the form of Teflon inserts. In this research low-cost and low-frequency (40 kHz) ACT is utilised. The use of the ACT-based wave generation together with the SLDV-based wave sensing give the possibility of realization of the full noncontact damage localization approach. Moreover, authors analysed the acoustic wave generation by the ACT and its propagation in the air using acousto-optic effect together with SLDV measurements.
In this paper results of damage assessment of composite panels using guided wave propagation phenomenon are presented. Elastic waves excitation is based on an air-coupled transducer (ACT) while the waves sensing is based on scanning laser Doppler vibrometry. It thus forms the full non-contact diagnostic approach. Thin panels made of fibre-reinforced polymer are investigated. The problem of optimal slope angle of ACT and the possibility of symmetric and antisymmetric elastic wave modes excitation is investigated. Research is related to the detection and localisation of artificial damage (additional mass, Teflon inserts). Moreover, the influence of single and multiple acoustic wave sources on artificial damage localization results and the problem of panel coverage area by elastic waves with large amplitudes to improve damage sensitivity are investigated. Different locations of ACTs and their influence on damage detection results are investigated. Two damage imaging algorithms based on elastic waves have been proposed, namely root mean square (RMS) energy maps and wavefield irregularity mapping (WIM). Moreover, results of simulations of elastic wave generation using ACT in CFRP plate based on a combination of FEM method and spectral element method (SEM) are presented. For this purpose COMSOL software and in-house MATLAB code are utilized, respectively
Evaluation of optimal slope angle of an air-coupled transducer (ACT) is important, to allow for effective generation of Lamb waves in solid structures. This effectiveness relies on both generation of desired wave modes, amplitude of measured signals and large coverage area for damage detection. Phenomenon of non-contact elastic waves generation in plate based on ACT is considered assuming few approaches. Numerical modeling in COMSOL is related to the analysis of different plate thicknesses and ACT excitation frequencies. Experimental research is based on wave excitation using piezoceramic ACT with a base excitation frequency of 40 kHz and SLDV measurements for a 1 mm-thick plate. A comprehensive investigation of optimal ACT slope angle for the generation of A0 mode is included. Propagation of S0 mode was not observed in numerical as well as experimental results. Optimal slope angle values were estimated in different ways numerically and experimentally with the use of dispersion curves and based on the amplitude of generated waves. Finally, the optimal angle value was determined and utilized for damage detection and localization problem in an aluminum plate.
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