Experimental observations of nonlinear effects of Lamb waves (II)

Based on the Ritec-SNAP system the experimental observations of nonlinear effects of Lamb waves have been carried out. Using the modal expansion analysis approach for waveguide excitation and the dispersion relations of Lamb waves, the conditions of cumulative second-harmonic generation of Lamb waves are briefly discussed. Wedge transducers with given oblique angles are used to generate and detect the fundamental waves and the second harmonics of the Lamb-wave propagation on the surface of an elastic plate. The physical meanings of the integrated amplitudes, both of the fundamental waves and the second harmonics, are expounded. The amplitudes of the fundamental waves and the second harmonics of Lamb waves on the plate surface are measured for different separations between the transmitting and receiving wedge transducers. In the vicinity of the driving frequency at which Lamb waves have strong nonlinearity, the quantitative relationships between the second-harmonic amplitudes and propagation distance are analyzed. Experimental results show that Lamb waves do have strong nonlinearity under certain conditions, and that the second harmonics of Lamb waves grow with propagation distance.