激光热弹激发涂层/基底系统中声表面波的有限元数值模拟
Numerical simulation of laser thermo-elastic generated surface acoustic waves by finite element method in coating/substrate systems
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摘要: 激光激发声表面波提供了评价涂层或薄膜的弹性性质的有效手段。考虑激光作用过程中材料热物理参数随温度变化的实际情况,在研究网格大小和时间步长这二个重要参数和求解稳定性的基础上,建立了优化的有限元模型数值模拟两种典型涂层基底系统中声表面波的激光热弹激发和传播过程。数值模拟结果表明:除了掠面纵波外,在快基底慢涂层系统中得到了正常的色散表面波,而在慢基底快涂层系统中得到了反常色散表面波。进一步,采取减小激发激光光斑的办法,使激发出来的声表面波频率高于慢基底快涂层系统中的截止频率时,在慢基底快涂层系统中得到了伪表面波。Abstract: Laser generated surface acoustic waves provide a useful tool for determining the elastic properties of coatings. Taking the temperature dependence of material properties into consideration, an optimized finite element is developed to simulate the laser thermo-elastic generation and propagation of surface acoustic waves in coating/substrate systems based on a well understanding of the influences of element size and integration time step on the solution stability. Besides the surface skimming longitudinal waves, a normal dispersive surface acoustic wave is observed in slow coating and fast substrate combination, while an anomalous dispersive surface acoustic wave is observed in fast coating and slow substrate combination, which confirm the validity of this model. Furthermore, a pseudo surface acoustic wave is observed in fast coating and slow substrate combination by decreasing the size of the laser spot, which allows generating higher frequency than the cutoff frequency of this system.