Use of Lamb waves to monitor plates: experiments and simulations

Abstract

Lamb waves at ultrasonic frequencies travel with little attenuation in thin elastic plates, and we demonstrate their use in pulse-echo behavior to monitor plate integrity. We envision using a single PZT wafer-type transducer to generate waves and to receive reflections from distant flaw or boundary locations. However, Lamb waves generally have multiple modes, each of them highly dispersive, and in consequence pulse dispersion can become pronounced and can make difficult or impossible the interpretation of pulse-echo responses. We show that selective generation of the S0 wave will overcome those difficulties; therefore, selection of transducer dimensions and pulse characteristics to achieve selective generation should be considered mandatory for most intended applications. We first review the work of others identifying a basic relationship between transducer dimension and excitation frequency for selective generation of the S0 wave. We then summarize our extensive experimental studies of wafer-type transducers with particular attention to S0 and A0 mode behavior, both in transmission and reception. We next report our two-dimensional finite element simulation of the same problem performed in FEMLAB, requiring transient simulation of the coupled electromechanical problem. We simulate the piezoelectric response of the wafer-type transducer coupled to the elastic plate, both as transmitter and receiver, as well as the development of Lamb waves within the source region and their subsequent propagation along the plate. Simulations illustrate the development and separation of the S0 and A0 modes and reproduce the expected group velocities and dispersion behavior. We show good agreement between our experiments and our simulations regarding S0 mode behavior, and we summarize the results to guide a designer in choosing transducer dimensions. In particular, good selectivity between the S0 and A0 mode generation can be obtained with appropriate choice of transducer size and center frequency. We show the results of experiments on an aluminum plate in which excitation of a single PZT wafer-type transducer at 6.5 V (peak-to-peak) produces reflected signals of ample strength (tens of mV) from distant boundaries and from partial thickness flaws.

A Survey of Scrutinizing Delaminated Composites via Various Categories of Sensing Apparatus

“…It was shown increasing the S 0 amplitude reflected from the right end of the delamination makes it appropriate for delamination detection. Performance of the wafer transducer to selectively actuate S 0 mode wave, as well as the capability of S 0 reflections from different depth located damages within undamaged and damaged signals being subtracted, measured via pulse-echo configured single wafer transducer for damage detection, have successfully been evaluated [50].…”

Sensitivity comparisons of layered Rayleigh wave and Love wave acoustic devices

“…An overall view on the effectiveness of FEM for modeling Ultrasonic Guided Wave behavior has been discussed [3]. Researchers have studied the dispersion characteristics and wave interference phenomena in plates [4][5][6], hollow cylinders/pipes [7][8][9], along with more arbitrary geometries such as rails [10][11][12]. These principles have also been extended to studying guided waves at interfaces [13,14].…”

A semi-baseline damage identification approach for complex structures using energy ratio correction technique

“…Several studies have used the Lamb waves‐based damage diagnosis for simple geometry components such as large plates so that they can detect notch cracks successfully . Furthermore, some other studies have utilized built‐in piezoelectric (PZT) transducers to monitor complex structural geometries, for example, lap joints .…”