为了探究管壁厚度对超声信号的产生与探测的影响, 采用有限元法建立了理想化的管道模型, 分别探究均匀管壁厚度变化和激发源处、接收端处及传播路径上等畸变管壁厚度的变化对超声信号产生的影响。结果表明, 当接收端处管壁厚度较薄时, 无法探测到可分辨的瑞利波信号; 传播路径上管壁厚度变小到一定程度后, 高频成分会出现明显的衰减, 但随着厚度的增大又会在一定程度内恢复。这一结果对激光超声在柱状、管状材料的无损检测中的进一步应用提供了有益的补充。

为了探究管道中瑞利波信号的产生、传播规律，基于热弹激发机制，建立了激光线源在偏心圆管侧面激发超声波的有限元模型，研究了在不同激发源厚度下及不同曲率半径下铝质圆管中瑞利波的产生、传播规律。结果表明，均匀薄管中，管壁厚度在一定程度上决定了所产生的超声信号的成分，并且在一定范围内,超声信号也会随着管壁厚度的变化而变化; 在非均匀管道中，激发源处的管壁厚度对超声信号的产生有很大影响，能在一定程度上决定超声信号的成分。这一结果对激光超声在管状材料的无损检测中的进一步应用是有帮助的。

基于热弹激发机制，建立了激光在圆柱侧面激发超声波的有限元模型，研究了在不同厚度及不同曲率半径下铝质圆柱(管)中头波的传播规律，分析了头波的传播特性。模拟结果表明：头波在柱体内部一定角度范围(临界角)内产生，并以略大于瑞利波的速度沿直线传播，在传播过程中逐渐远离瑞利波，并向纵波逼近；临界角(最大振幅处)的正弦值近似等于柱体中瑞利波与纵波的波速之比；在界面处，一部分头波渗透出来沿周向传播，并迅速衰减，另一部分则发生反射，沿直线传播至界面处渗出，没有发生明显的衰减。

Laser shock peening is a well-known method for extending the fatigue life of metal components by introducing near-surface compressive residual stress. The surface acoustic waves (SAWs) are dispersive when the near-surface properties of materials are changed. So the near-surface properties (such as the thickness of hardened layers, elastic properties, residual stresses, etc.) can be analyzed by the phase velocity dispersion. To study the propagation of SAWs in metal samples after peening, a more reasonable experimental method of broadband excitation and reception is introduced. The ultrasonic signals are excited by laser and received by polyvinylindene fluoride (PVDF) transducer. The SAW signals in aluminum alloy materials with different impact times by laser shock peening are detected. Signal spectrum and phase velocity dispersion curves of SAWs are analyzed. Moreover, reasons for dispersion are discussed.

激光冲击硬化通过在材料的近表面产生残余压应力来提高材料的表面硬度和抗疲劳寿命。材料近表面性质的变化能够导致在其中传播的声表面波发生色散。为了研究激光冲击硬化后金属Al合金样品中的激光声表面波(SAW)的传播, 提出一种合理的宽带激发和接收方法, 搭建了由激光激发、聚偏二氟乙烯(PVDF)传感器接收超声信号的实验装置。分别对不同条件下激光冲击的Al合金样品中的激光声表面波进行了探测, 通过对接收到的超声信号进行时频分析得到了信号的频谱以及声表面波的相速度色散曲线, 速度色散主要是由于晶粒方向改变和错位密度的增加引起的。

利用激光激发声表面波及光差分技术研究激光源对声表面波的影响。实验中利用了Nd∶YAG脉冲激光器激发超声，采用632nm的He－Ne激光器基于光束偏转法的光差分检测系统，测量了铝样品表面的声表面波，获得了很好的信号。在此基础上研究了激发源的形状和能量对激发的声表面波幅度的影响。同时从热弹和融蚀机制下讨论激光声表面波的产生。在这两种机制下，声表面波的幅度发生了很大的变化。随着激光能量密度的增加，声表面波的幅度由线性变化转换为非线性变化。这一结果对激光激发声表面波理论研究有一定的指导意义。

In the field of nondestructive evaluation, laser generation and detection of the surface acoustic waves (SAWs) are potentially useful for investigating material surfaces. SAW generated by laser line source is carried out on a kind of optical difference detection system based on optical beam deflection technique. The setup is simple and easy to adjust. Furthermore the system has advantages such as high efficiency of photo-electricity conversion, high frequency responding, the ability of ant-intervene and broadband detection etc.. It can be used not only to receive SAW, but also to detect surface-breaking defects in material. The experimental results verify that the SAWs generated by a line source have the advantages of powerful signal and good directivity. SAWs have been excited on sample aluminum with artificial surface-breaking defects. From the experiment, we attain the characters of reflected wave and transmitted wave by SAW interacted with the surface-breaking defects.