The work presents the metrological evaluation of the modified hybrid spectrum decomposition and zero-crossing technique. The presented technique enables to reconstruct the phase velocity dispersion curve part of Lamb wave modes using only two signals. This is set to consequently simplify the of complex guided wave signals analysis. Experimentally measured asymmetric A 0 mode Lamb wave signals propagating in 4 mm thickness non-homogeneous Glass Fibre Reinforced Plastic (GFRP) plate are used for assessment of the proposed technique. The phase velocity dispersion curve (DC) segments are obtained using three different filter bandwidths as reference using the DC obtained by the semi-analytical finite element method SAFE. The proposed technique quantitative and qualitative characteristics are presented. Using this technique and employing various band-pass filters it is shown that the DC segments are reconstructed in approximately 50%-88% bandwidth of the incident signal frequency spectrum. The average of the calculated expanded uncertainties for all filter bandwidths is equal to approximately 2%. The narrower filter bandwidth has produced smaller systematic errors equal to 1.8%, yielding to wider reconstructed dispersion curve segments.
In the previous our article the technique for measurement of the group velocity using spectrum decomposition was proposed and demonstrated on the signals obtained from the finite element modelling. The objective of this work is to check this technique using experimental signals. The experiments were carried out on the 2mm thickness aluminium plate with dimensions 1100mm x 620mm. The guided waves were generated using a wide band contact type transducer. The excitation signal was 300 kHz, 3 periods burst with the Gaussian envelop. The signals were processed using the proposed spectrum decomposition algorithm and corresponding segments of the group velocity dispersion curves of the A 0 and the S 0 modes of Lamb waves were obtained. The analysis demonstrated that scattering and errors of the results essentially depends on the bandwidth of the filter used for decomposition. So, it is necessary to select parameters of the filters separately for each mode under investigation. The obtain results were compared with the theoretical dispersions curve and good correspondence was obtained.
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