Nonlinear feature of phase matched Lamb waves in solid plate

The measurement of second harmonic Lamb waves is investigated as a promising feature extraction technique to characterize material nonlinearity in plate-like structures. In general, the effect of second harmonic generation can be weak, due to the dispersive nature of Lamb waves. The phase matched Lamb modes are explored to generate the second harmonics with a cumulative growth effect. Among all phase matched Lamb modes, it is of particular interest to find the most suitable Lamb modes for improving the efficiency of second harmonic generation and reception. Analytical expressions and experimental observations of second harmonic generation of Lamb waves in an isotropic plate with weak nonlinearity, are presented in this paper. Nonlinear parameters of Lamb waves are derived in this paper for the first time as a function of signal frequency, wave mode and geometric parameters of waveguides. Nonlinear features of various phase matched Lamb modes are discussed for the comparison of efficiency of second harmonic generation. The experimental results are found to be consistent with the theoretical predictions in a qualitative manner. This study shows that physics based feature selection is essential for efficient generation and reception of second harmonic Lamb waves. (C) 2019 Elsevier Ltd. All rights reserved.