Reconstruction of Lamb Wave Dispersion Curves in Different Objects Using Signals Measured at Two Different Distances

The possibilities of an effective method of two adjacent signals are investigated for the evaluation of Lamb waves phase velocity dispersion in objects of different types, namely polyvinyl chloride (PVC) film and wind turbine blade (WTB). A new algorithm based on peaks of spectrum magnitude is presented and used for the comparison of the results. To use the presented method, the wavelength-dependent parameter is proposed to determine the optimal distance range, which is necessary in selecting two signals for analysis. It is determined that, in the range of 0.17-0.5 wavelength where δcph is not higher than 5%, it is appropriate to use in the case of an A₀ mode in PVC film sample. The smallest error of 1.2%, in the distance greater than 1.5 wavelengths, is obtained in the case of the S₀ mode. Using the method of two signals analysis for PVC sample, the phase velocity dispersion curve of the A₀ mode is reconstructed using selected distances x₁ = 70 mm and x₂ = 70.5 mm between two spatial positions of a receiving transducer with a mean relative error δcph=2.8%, and for S₀ mode, x₁ = 61 mm and x₂ = 79.7 mm with δcph=0.99%. In the case of the WTB sample, the range of 0.1-0.39 wavelength, where δcph is not higher than 3%, is determined as the optimal distance range between two adjacent signals. The phase velocity dispersion curve of the A₀ mode is reconstructed in two frequency ranges: first, using selected distances x₁ = 225 mm and x₂ = 231 mm with mean relative error δcph=0.3%; and second, x₁ = 225 mm and x₂ = 237 mm with δcph=1.3%.