Laser-generated like-Rayleigh waves propagation in viscoelastic adhesive coating/substrate structures

We have studied the propagation characteristics of laser-generated like-Rayleigh waves in viscoelastic adhesive coating/substrate structures. Considering the viscoelasticity of the coating and substrate, we have established the finite element models in frequency domain for the laser-generated like-Rayleigh waves in the epoxy coating/aluminum substrate, epoxy coating/brass substrate, and epoxy coating/foam substrate systems, respectively. In addition, we have investigated the waveform and propagation characteristics of the like-Rayleigh waves and studied the influences of the transparency, thickness, and viscoelasticity of the epoxy coating and the viscoelasticity of the substrate on the propagation characteristics of the like-Rayleigh waves. Moreover, we have also verified the results by the theoretical phase velocity and attenuation curves. The results show that the coating viscoelasticity can induce the attenuation characteristics of the higher frequencies of the like-Rayleigh waves, but has little effect on the lower frequencies, and the substrate viscoelasticity has the influences on both the higher and lower frequencies of the like-Rayleigh waves, especially the lower frequencies. Furthermore, the mode and dispersive characteristics of the like-Rayleigh waves are closely related to the substrate. This study provides a useful theoretical basis for inverting mechanical parameters and evaluating the adhesive quality of the viscoelastic adhesive coating/substrate structures.