兰姆波非线性效应的实验观察

Experimental observations of nonlinear effects of Lamb waves

对兰姆波非线性效应进行了实验观察。首先,对实验所采用的Ritec系统进行了介绍,尤其对实验系统的声学部分进行了详细考虑,特别是对二次谐波的时域响应进行了简洁直观的分析。根据兰姆波具有强烈非线性效应的条件,采用斜劈换能器发射和接收兰姆波。改变发射与接收斜劈换能器的间距,对一定频率范围内的兰姆波及二次谐波在固体板表面的振幅进行了测量。在基频与二倍频兰姆波相速度相等所对应的频率附近,分析了二次谐波振幅随传播距离的定量关系,从实验上证实了二次谐波在传播过程中具有积累增长效应的结论。

The experimental observations of nonlinear effects of Lamb waves have been reported. Firstly, the brief descriptions have been made for the nonlinear acoustic measurement system developed by Ritec. The detailed considerations of acoustic experiment system established for observing nonlinear effects of Lamb waves have been carried out. Especially, the analysis focuses on the time-domain responses of second harmonics of Lame waves by employing a straightforward model. Based on the existence condition of strong nonlinearities of Lamb waves, the wedge transducers are designed to generate and detect Lamb waves in aluminum plate. For the different space distance between the transmitting and receiving wedge transducers, the amplitudes of the fundamental and second-harmonic Lamb waves on the plate surfaces have been measured within a given frequency range. In the near range of a frequency where the fundamental and the double frequency Lamb waves have the same phase velocities, the quantitative relations of second-harmonic amplitudes on propagation distance have been analyzed. It is experimentally verified that the second harmonics of Lamb waves do have cumulative growth effects.