兰姆波非线性效应的实验观察(Ⅱ)

Experimental observations of nonlinear effects of Lamb waves (II)

基于Ritec-SNAP系统对固体板中传播的兰姆波的非线性效应进行了实验观察。根据导波的模式展开分析方法和兰姆波的频散曲线,简述了兰姆波的积累二次谐波发生条件。采用一定倾角的斜劈换能器在固体板表面激发和接收兰姆波的基波和二次谐波时域信号,阐述了兰姆波的基波、二次谐波时域脉冲包络的积分振幅的物理意义,在固体板表面分别测量了不同传播距离的兰姆波的基波、二次谐波的幅频曲线。在兰姆波具有非线性效应的频率值附近,分析了兰姆波的二次谐波振幅随传播距离的变化关系。实验结果进一步证明了兰姆波在一定条件下具有强烈的非线性效应,其二次谐波表现出随传播距离积累增长的性质。

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, is 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-harmonlc 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.