Point-to-Point Dispersion Estimation of Lamb Waves

Abstract

This paper presents a methodology for estimating group velocities of Lamb waves without requiring prior knowledge of material properties. First, inspired by the FRF approach, the concept of Pseudo time-frequency distribution (PTFD) is introduced to identify the wave component over a relatively wide frequency range from a single measurement. Next, the MDPORE method is used to detect the Time-of-Arrival (ToA) ridge of each mode. The ToA ridge is then employed to calculate the group-velocities, which are further smoothed using an S-G filter. The calculated results are then converted into a wavenumber representation to determine the reference time span of the target mode wave packet at a given distance. Based on this, the direct wave component is extracted from the response and used to calculate the confidence index, which assess the non-linear spectrum modulation of the travelling wave packet. Multiple PTFDs, each with different cycle numbers tone burst excitation, are employed to perform ridge detection for group velocity calculation and confidence level evaluation. Finally, the group-velocity result corresponding to the maximum confidence level is selected as the final result at each frequency point. Numerical and experimental responses of aluminum plates are used to validate the feasibility and robustness of the proposed dispersion estimation method.