Experimental observations of nonlinear effects of SH plate wave propagation in a solid plate

The effect of second-harmonic generation of SH plate wave propagation in a solid plate was briefly analyzed theoretically using perturbation approximation and modal expansion approach for waveguide excitation.Although the effect of second-harmonic generation of a single shear wave in an infinite solid is weak,a SH plate wave consisting of two shear waves in a solid plate may have a strong nonlinear effect under certain conditions.This paper focused on the experimental verification of the said theoretical prediction.Both the shear-wave wedge transducer for excitation of SH plate waves and the liquid wedge transducer for receiving the signals of second harmonics were manufactured,and the experimental system for studying the nonlinear effects of SH plate wave propagation was established.Through the theoretical analyses in detail and the comparative experimental investigations,it was clarified that the clear second- harmonic signal observed under certain conditions was due to the strong nonlinear effect of SH plate wave propagation. Moreover,the amplitude-frequency curves of second harmonics,with respect to the different distances of SH plate wave propagation,were measured in the far-field regions.The relationship between the second-harmonic signals of the SH plate wave and the propagation distance was analyzed near the specific frequency at which the phase velocity of a SH plate wave was equal to that of a double frequency symmetric Lamb wave.It was experimentally verified that,under certain conditions,the second-harmonic amplitude of SH plate wave propagation could grow with propagation distance, namely,SH plate wave propagation could have a strong nonlinearity.