Measurement of the group velocity of Lamb waves in aluminium plate using spectrum decomposition technique

Abstract

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.

Dispersion curve estimation via a spatial covariance method with ultrasonic wavefield imaging

“…Besides that, the high errors in the estimation is also because the bandwidth set in the bandpass filter during the signal acquisition in the in-line filter since the bandwidth of the filter has the influence in the phase velocity estimation [18]. The mean relative errors of S0 mode waves at 100 kHz were the highest among the measurements.…”

“…Another signal decomposition technique is the chirplet matching decomposition [9,17], and it demonstrated better efficiency than the cross-correlation technique with acceptable error of around 2% [9]. A spectral decomposition technique was proposed [18,19] as well to develop the group velocity curves of Lamb waves in an aluminum plate. The method enabled to reconstruct the dispersion curves of the fundamental modes with relative errors around 2%.…”

Investigation of the Spectrum Decomposition Technique for Group Velocity Measurement of Lamb Waves Propagating in CFRP Composite Plate

“…However there are two important questions: what bandwidth of the filter should be selected and to which frequency calculated group velocity should be related. It was determined that most correct is to relate group velocity to the central frequency of the filtered signal [2]. More complicated question is selection of the filter bandwidth.…”

“…In previous articles [1], [2] the method for measurement of the group velocity of guided waves based on the application of the spectrum decomposition technique was presented. The spectrum decomposition technique was already used for investigation of ultrasonic signals propagating in attenuating media [3] and for estimation of phase velocity [4].…”

A phase velocity filter for the measurement of lamb wave dispersion

“…This however is time consuming. For measurement of group velocity, from which phase velocity can be derived [9], spectral decomposition can be used [15].…”