Investigation of the spectrum decomposition technique for estimation of the group velocity Lamb waves

Abstract

Phase velocity, group velocity and attenuation of guided waves are most important parameters in their applications for non-destructive testing. In previous our articles the investigations technique for measurement of the phase velocity was proposed. However this technique is not applicable for evaluation of the group velocity. The objective of the work presented was to develop a technique which enables estimation of the group velocity taking into account dispersion of the guided waves. As the result of the investigation the technique based on the spectrum decomposition approach was proposed. Performance of the technique is demonstrated on the modelled signal. In the investigation signals propagating in the finite element model of the 2 mm thickness and 200 mm length aluminium plate were used. The asymmetric A0 mode was excited by adding a shear force to one of the plate end and the S0 mode - by adding a normal force. The excitation signal was 3 periods, 300 kHz burst with the Gaussian envelope. In general, the investigation demonstrated that, the proposed spectrum decomposition technique enables to reconstruct the segments of the dispersion curves of the group velocity both in the cases of the asymmetric A0 and the symmetric S0 modes of Lamb waves in the analyzed frequency range.