This paper presents the improved thickness estimation technique using Steady-state excitation Continuous-scanning Laser Doppler Vibrometery(SCLDV).
In this study, the wavenumber sensitivity with respect to the thickness variations of a structure, along with the information of wave modes, is utilized to find an optimal interrogation frequency band for SCLDV. In addition, the use of multi-frequency steady-state response is used to improve the accuracy of the thickness variation. By utilizing the wavenumber sensitivity along with the multi-frequency excitations, the proposed SCLDV shows the improved depth estimation, compared to the previous approaches which empirically select the interrogation frequency.
For validation of this technique, several experiments were performed on steel plates, which contain corrosion damage with various depth variations. The results showed that the proposed technique is very efficient in detecting and visualizing very small thickness variations of a structure at high speed.
This paper presents the comparison study of wavenumber-based defect detection performance in full field laser scanning techniques. Two types of wave excitation are used for damage detection; guided waves and standing waves. A piezoelectric actuator is mounted on surface of the thin plate to generate guided and standing waves with a single excitation frequency. Subsequent responses on each grid point are measured using a Laser doppler vibrometer (LDV) with a mirror tilting device. Full field wave image is then generated from the measured wave signals. After the laser scanning, wavenumber based processing is applied to the measurements to generate two types of full wave field images and to detect structural damage. Three wavenumber based signal processing are applied to the wave filed images to estimate damage size and depth, including the Local wavenumber mapping, Acoustic Wavenumber Spectroscopy, 2D wavelet based wavenumber spectroscopy. For the comparison of these two techniques, several experiments are performed on thin walled structures with several different types of damage, including corrosion in an aluminum plate and debonding on composite plates. This paper outlines pros and cons of these two excitation techniques in terms of several parameters, including damage sensitivity, processing time and their applicability.
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