Study on crack scattering in aluminum plates with Lamb wave frequency-wavenumber analysis

The multimodal characteristic of Lamb waves makes the interpretation of Lamb wave signals difficult in either the time or frequency domain. In this work, we present our study of Lamb wave propagation characterization and crack scattering using frequency-wavenumber analysis. The aim is to investigate three dimensional (3D) Lamb wave behavior in the presence of crack damage via the application of frequency-wavenumber analysis. The analysis techniques are demonstrated using simulation examples of an aluminum plate with a through-thickness crack. Both in-plane and out-of-plane components are acquired through a 3D elastodynamic finite integration technique (EFIT), while the out-of-plane component is also experimentally obtained using a scanning laser Doppler vibrometer for verification purposes. The time-space wavefield is then transformed to the frequency-wavenumber domain by a two dimensional (2D) Fourier transform and the out-of-plane EFIT results are compared to experimental measurements. The experimental and simulated results are found to be in close agreement. The frequency-wavenumber representation of in-plane and out-of-plane components shows clear distinction among various Lamb wave modes that are present. However, spatial information is lost during this 2D transformation. A short space 2D Fourier transform is therefore adopted to obtain the frequency-wavenumber spectra at various spatial locations, resulting in a space-frequency-wavenumber representation of the signal. The space-frequency-wavenumber analysis has shown its potential for indicating crack presence.