单层和双层材料中的脉冲激光超声数值模拟

用有限元方法数值模拟激光热弹机制激发单层和双层材料中的超声波。分别建立激光在单层和双层材料中激发瞬态温度场和热弹机制激发超声波场的有限元模型，该模型考虑了激光作用过程中材料的热物理参数依赖于温度的特性。在单层铝板的厚度小于激光激发的超声波的中心波长时，数值模拟得到了兰姆波，主要是低频的非色散的对称模和色散的反对称模。随着铝板厚度的增加，更高阶的模式可以在板中传播，波形向表面波转化，得到了掠面纵波和瑞利波。进一步计算了Ni／Al和Al／Cu这两种双层材料中的不同接收距离处的垂直表面位移。由于表面波中的高频成分透入深度浅，在传播过程中受薄膜(涂层)的影响较大，而低频成分在传播过程中受基底的影响较大，因此在Ni／Al系统中得到了正常色散而在Al／Cu系统中得到了反常色散现象。

Numerical Simulation of Pulsed Laser Induced Ultrasound in Monolayer and Double Layer Materials

Taking account of the temperature dependence of the thermal physical parameters, the thermoelastic generated ultrasound and transient temperature fields by pulsed laser in mono layer and double layer materials are numerical simulated by finite element method. In the mono layer plate, whose thickness is less than the central wavelength of the generated ultrasound, Lamb wave, mainly with a non dispersion symmetric mode and a dispersion anti symmetric mode, is obtained by numerical simulation. When the sample thickness increases so that the higher modes can propagate in the plate, a skimming surface longitudinal wave and a Rayleigh wave are formed at the sample surface. Furthermore, the normal displacement on the surface of two kinds of two layer system, one is Ni/Al systems and the other is Al/Cu system, is calculated. Because the high frequency surface acoustic wave due to less penetration depth is more influenced by the properties of the surface layer during propagating and the low frequency surface wave is more influenced by the substrate, normal dispersion is observed in Ni/Al system and anomalous dispersion is observed in Al/Cu system, respectively.