Plate Waves Scattering Analysis and Active Damage Detection

Abstract

This study investigates and evaluates the technology of using plate waves to detect the locations and sizes of circular holes and cracks in plates. Piezoelectric ceramic discs surface-mounted on both sides of an aluminum alloy plate were used as narrow-frequency plate wave actuators and sensors, and the antisymmetric plate wave signal was analyzed by wavelet transform in the time-frequency domain. The damage location and frequency spectrum characteristics were identified by the wave through time-of-flight difference and signal analysis of the damage scattered wave group. The plate wave signal of the damaged plate included the scattered wave signal and the plate wave signal transmitted directly between the piezoelectric discs. Under ideal conditions, the plate wave signal indicating damage can be obtained by subtracting the plate wave signal in a plate without damage from the plate wave signal scattered from actuators to sensors. This study established an optimization program based on the simplex algorithm to inversely calculate the location of the plate damage. The developed damage location objective function has a unique global minimum value that can ensure the accuracy of the damage location calculation, and good results were obtained in experiments. The spectral characteristics of the scattered plate wave were related to the type, size, wave propagation path, and incident angle of the damage. Numerical analyses of scattered spectra for various damages are needed as references to compare with experimental results in the future.

The Usefulness and Limitations of Ultrasonic Lamb Waves in Preventing the Failure of the Wind Turbine Blades

“…Two-dimensional Fast Fourier Transform (2D-FFT), Short-Time Fourier Transform (STFT), Wavelets Transform (WT) and its variations, Wigner-Ville Distribution (WVD) and its variations, etc. [49,58,62] have been used for dispersion evaluation of Lamb waves. In many cases, the reliability of the method is not conducted and presented.…”

“…As the signals of the dispersing modes consist of different frequency components that propagate with different velocities depending on the distance, it influences the waveform distortion: the signal is elongated, and the peak amplitude is decreased (Figure 7b-d). This phenomenon complicates the analysis of the received signals and detection of defects [56][57][58]. The halving effect of the signal amplitude (at a level of 0.5 or −6 dB) is one of the main parameters in estimating the location and size of the defect in ultrasonic NDT.…”

Confluence Effect of Debris-Filled Damage and Temperature Variations on Guided-Wave Ultrasonic Testing (GWUT)

“…The propagating stress wave is constrained by the boundaries of the structure (waveguide), hence the guided wave. The wave interaction with the structure, especially with damage or discontinuity, causes scattering, reflections, mode conversion, and some energy absorption at the damaged spot [28]. Figure 2b depicts the effect of wave-damage interaction.…”

Reconstruction of Lamb Wave Dispersion Curves in Different Objects Using Signals Measured at Two Different Distances

“…Multiple methods have been used for signal analysis: two-dimensional Fast Fourier Transform (2D-FFT), Short-Time Fourier Transform (STFT), Wavelets Transform (WT) and its variations, matching pursuit algorithms, Wigner-Ville Distribution (WVD) and its variations, etc. [1,[13][14][15][16][17][18], or signal processing methods used for phase velocity and wavenumber estimation [19,20]. However, the named methods require signals collection at many points along the wave propagation path for the reconstruction of dispersion curves of Lamb waves.…”