Structural Health Monitoring System Using Piezoelectric Networks with Tuned Lamb Waves

Abstract

Abstract. The paper presents a structural health monitoring system based on propagation of tuned Lamb waves and their interference with discontinuities. The dispersion curves are studied to determine the appropriate type and dimension of transducers and to select the optimum scanning frequencies and relevant propagation modes. A piezoelectric sensor network was implemented in an aluminum plate in order to generate and to sense the wave propagation and associated reflections. The algorithm developed for damage detection relies on the comparison of undamaged and damaged responses of the structure. Combinations of filters and statistical methods were applied to detect differences in the sensor signals acquired for the two different states (damaged and undamaged), corresponding to damage reflections. In order to eliminate the false positives due to noise, a probability analysis is performed to obtain the final damage position. The software designed for the current application allows the automatic calculation of dispersion curves, it executes the scans, performs data processing, executes the detection algorithm and presents the probable damages and their positions in a graphical form. Experiments were performed with the introduction of cumulative damages in the plate such as surface and through-the-thickness holes and cuts, ranging from 7 mm to 1 mm in diameter. Additionally, a stringer was attached to the plate by a single rivet line to simulate an aircraft skin structure. Cuts originating from rivet holes and connecting adjacent rivets, as well as loosened rivets were detected by the system. The introduction of the stringer resulted in a loss of precision in the determination of the radial position of the damages near it. Also, the network revealed significant difficulties in the detection of damages beyond the stringer.

Damage Detection of Composite Plates by Lamb Wave Ultrasonic Tomography with a Sparse Hexagonal Network Using Damage Progression Trends

“…If a simple sine wave composed of a few cycles is emitted then the desired frequency can be actuated; however, the frequency domain of such a signal shows small secondary peaks in the frequency domain that are present at other frequencies. To eliminate these peaks the signal can be modulated with a window function to slowly increase and decrease the magnitude of the signal [18]. A commonly used signal that provides a good compromise between number of cycles and ramp up rate consists of five sine peaks modulated by a Hann window.…”

Development of Generic Methodology for Designing a Structural Health Monitoring Installation Based on the Acoustic Emission Technique

“…It was suggested that the maximum excitation and detection of a particular Lamb wave mode can be achieved when the length of the transducer equals half of its wavelength. This behaviour is generally referred to as Lamb wave tuning as a transducer can be designed to be sensitive to a particular wave mode and almost completely insensitive to another wave mode at the same frequency [10]. Figure 4 shows this effect for a 7 mm long piezoelectric transducer and 2 mm thick aluminium sheet, where the strain response of the transducer with respect to the wave modes can be seen for different values of frequency [11].…”

A method to compensate non-damage-related influences on Damage Indices used for pitch-catch scheme of piezoelectric transducer based Structural Health Monitoring

“…One of the most investigated approaches to develop SHM system is based on excitation of elastic waves by a network of piezoelectric transducers (PZTs) integrated with the monitored structure. 2,[4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Elastic waves can propagate significant distances, and they are sensitive to local structure discontinuities and deformations. Thus, by virtue of their nature, they can be used for damage detection, irrespective of the type of the material used for aircraft manufacturing.…”