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以平面应变理论为基础,从弹性动力学平衡方程出发,推导得到频域动力学平衡方程。忽略材料的粘性特征,分别在时域和频域中建立激光激发兰姆(Lamb)波的有限元数值模型。比较分析两种模型的求解过程,在此基础上,在频域中研究激光作用在粘弹性薄板上激发Lamb波的特征。结果表明,激光激发的Lamb波主要包含低频的弱色散的对称模和色散的反对称模;有限元频域模型能有效地处理粘弹性材料中Lamb波的传播问题;材料的粘性特征会引起Lamb波的振幅衰减,且不同模式波的衰减(因子)不同。
Based on the plane strain theory, based on the elastic-dynamic equilibrium equation, the dynamic equilibrium equation in the frequency domain is deduced. Neglecting the viscous characteristics of the material, a finite element numerical model of the Lamb wave excited by the laser is established respectively in the time domain and the frequency domain. The solving process of the two models is compared and analyzed. Based on the above analysis, the characteristics of the Lamb wave excitation on viscoelastic thin plate are studied in the frequency domain. The results show that the Lamb wave excited by the laser mainly contains low-frequency symmetrical modes of weak dispersion and anti-symmetric modes of dispersion. The finite-element model can effectively deal with the propagation of Lamb waves in viscoelastic materials. The viscous characteristics of materials can cause Lamb Wave amplitude attenuation, and the attenuation of different mode wave (factor) is different.