零群速度（ZGV）Lamb波是Lamb波在某些频率点处的特殊模式，其群速度为零，而相速度是有限值，在频谱曲线上会出现尖锐共振峰。近年来已探测到ZGV Lamb波并成功应用于板的弹性常数、泊松比测量、板厚和板厚分布的测试、两块板之间的粘结刚度检测等。但目前大部分ZGV Lamb波的研究均针对单层板或中心对称双层板，且均集中于线性范围内。本项目拟采用激光j激发和探测技术，从理论和实验两方面研究非对称双层板中ZGV Lamb波。研究其分布特征，阐明材料厚度、力学参数等等对ZGV点的影响规律；研究弱连接等损伤对零群速度Lamb波的线性和非线性作用，特别是迟滞非线性引起的与振幅相关的ZGV点位置移动和ZGV Lamb波的衰减，实现ZGV的频率漂移和吸收等效应的定量探测；研究这些非线性效应与弱连接程度之间的定量关系，以此探索发展新的ZGV Lamb波无损检测原理和技术。

Zero group velocity (ZGV) lamb mode is a special Lamb wave mode whose group velocity vanishes with a finite phase velocity at some certain frequencies, so it appears as sharp resonant peak in the frequency range. In recent years, ZGV mode has been successfully detected and applied in characterization of elastic properties, thickness gauge and adhesion quality evaluation. These researches were focused in linear regime in single plates or symmetrical bi-layers. This proposal aims of the linear and nonlinear ZGV modes in non-symmetrical bilayers by laser ultrasound. We try to clarify the influence of material thickness, mechanical parameters on ZGV frequencies on the basis of a thorough study into the ZGV distribution characteristics in bilayers. Then the linear and nonlinear effects of weakly connected or unbonded damage on ZGV mode will be investigated, in particular, the move of the ZGV position and the attenuation of ZGV mode caused by the hysterestic non-linearity. Furthermore, we will focus on accomplishing the quantitative detection of the frequency drift and absorption of ZGV experimentally. Finally, we expect to give the quantitative relation between these nonlinear effects and the degree of weak connection so that we can develop a new nondestructive testing principle and technology by using nonlinear ZGV Lamb mode.