激光激发单模兰姆波的有限元模拟

Simulation of Laser-Generated Single-Mode Lamb Wave by Finite Element Method

针对激光超声技术中如何提高超声信号强度的问题,建立激光作用在铝板材料中激发超声波的理论模型,采用有限元方法对环状阵列激光源激发的超声波进行数值模拟。通过调节环状激发源的个数及间距,优化加载模型,得到了超声信号强度和信噪比均较高的加载模型结构。并利用FFT变换提取出超声信号的频率,计算出超声兰姆波波包的群速度。结果表明,该加载模型下激发的超声模式为能量高、频散小、且在整个板内部均有一定振动能量的A0模式兰姆波。这一结果可对激光超声无损检测中激发光源的选择和模式优化有一定参考价值。

In order to improve the intensity of ultrasound signal,a Laser-ultrasonic excited by ring array laser source is simulated using finite element method based on the theoretical model of Laser-ultrasonic generated in aluminum plate.The optimum load model with the high signal strength and the high signal to the noise ratio is obtained through the adjustment of the number of excitation source and spacing.Then,the frequency of ultrasonic signals is extracted by using FFT transform and the group velocity of ultrasonic packet is calculated.Results indicate that the Laser-ultrasonic generated by the ring array laser source is the A0mode of Lamb wave.It has high energy and small dispersion,and always keeps sufficient vibration energy in the entire internal board.The simulation result can provide some useful reference data for selecting laser excitation source and optimizing models in Laser-ultrasonic nondestructive test.