Determination of group velocity of propagation of Lamb waves in aluminium plate using piezoelectric transducers

Robert Zemčík,Zuzana Lašová

doi:10.24132/acm.2017.346

Robert Zemčík, Zuzana Lašová

Open Access

https://doi.org/10.24132/acm.2017.346

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Abstract

A prior knowledge of group velocities of Lamb wave modes is a key for analysis of time signals in guidedwave based structural health monitoring. The identification of multiple wave modes may be complicated due to dependency of group velocity on frequency (dispersion). These dependencies for infinite plate of constant thickness can be calculated by a numerical solution of analytic equation. Two alternative approaches to determine group velocities of zero-order Lamb wave modes in aluminum plate were used in this work: Two-dimensional Fast Fourier Transform (2D-FFT) and methods of time-frequency processing. 2D-FFT requires a high number of time signals in equidistant points, therefore it was applied on data from finite element analysis of wave propagation in the plate. Group velocities for chosen frequencies were also determined using wavelet transform (WT) of signals as differencies of times of arrival measured by a pair of piezoelectric transducers. The results from 2D-FFT and wavelet transform were compared to the analytic solution.

Highlights

Lamb waves attracted scientific interest in recent years due to their potential use in the structural health monitoring (SHM, automated structural defect detection)
Dispersion curves of two zero-order Lamb wave modes in aluminum plate were obtained by two methods: two-dimensional Fourier transform applied on data from the finite element analysis and measurement using piezoelectric transducers
2D-FFT provides well approximated dispersion curves in k-f domain, which correlate with dispersion curves calculated by solution of Rayleigh-Lamb equation

Summary

Introduction

Lamb waves attracted scientific interest in recent years due to their potential use in the structural health monitoring (SHM, automated structural defect detection). Lamb waves are dispersive, which means their group and phase velocities depend on frequency. These dependencies for each Lamb wave mode are called dispersion curves and can be calculated by numerical solution of Rayleigh-Lamb equation [5]

Results

Conclusion