Numerical simulation of laser thermo-elastic generated surface acoustic waves by finite element method in coating/substrate systems

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.