Validation of Dispersion Curve Reconstruction Techniques for the A₀ and S₀ Modes of Lamb Waves

Abstract

The properties of ultrasonic Lamb waves, such as relatively small attenuation and high sensitivity to structural changes of the object being investigated, allow performing of non-destructive testing of various elongated structures like pipes, cables, etc. Due to the dispersion effect of Lamb waves, a waveform of the received informative signal is usually distorted, elongated and overlapping in the time domain. Therefore, in order to investigate objects using the ultrasonic Lamb waves and to reconstruct the dispersion curves, it is necessary to know the relationship between frequency, phase and group velocities and thickness of the plate. The zero-crossing technique for measurement of phase velocity of Lamb waves (the A0 and S0 modes) has been investigated using modelled dispersed signals and experimental signals obtained for an aluminium plate having thickness of 2 mm. A comparison between two reconstruction methods of Lamb wave phase velocity dispersion curves, namely, the two-dimensional fast Fourier transform (2D-FFT) and zero-crossing technique, along with the theoretical (analytical) dispersion curves is presented. The results indicate that the proposed zero-crossing method is suitable for use in reconstruction of dispersion curves in the regions affected by strong dispersion, especially for the A0 mode.

Acoustic emission wave propagation in honeycomb sandwich panel structures

“…The interception of the trending equation with the Y-axis. The attenuation behaviour of both Lamb wave modes in the GFLP alone is as expected; despite the greater dispersion of the Ao mode [31], the So mode experiences greater attenuation due to its higher frequency [32]; the So mode also experiences greater directional dependency due to the increase in scattering which occurs when propagating off-fibre direction [33]. A drop in the amplitude of both wave modes can be seen as the structural complexity increases from a thin GFLP to a complex as described by the aforementioned insertion loss.…”

Metrological Performance of Hybrid Measurement Technique Applied for the Lamb Waves Phase Velocity Dispersion Evaluation

“…5). At first, these methods were used separately to evaluate the Lamb waves phase velocity (zero-crossing method) [35] and group velocity (spectrum decomposition method) [36] dispersion characteristics and to reconstruct the dispersion curve segments. The uncertainty quantification for both techniques has been completed accordingly to previous works [37], [38].…”

2D Analytical Model for the Directivity Prediction of Ultrasonic Contact Type Transducers in the Generation of Guided Waves

“…In comparison to other UGW testing methods, Lamb wave testing is fast and more sensitive to the surface and internal defects over the thickness of the structure. [ 3 , 4 , 5 ]. Although UGW testing is an effective technique for the inspection of defects a few meters away from the transmitting transducers, defects may be located at longer distances [ 6 , 7 ].…”