Numerical simulation of Rayleigh wave interaction with surface closed cracks under external pressure

A finite element model is proposed to investigate the nonlinear interaction between Rayleigh waves and a surface closed crack of different depth. The closed crack is numerically modeled by an interface of hard contact with Coulomb friction. Due to the coupling effect between the normal and tangential displacements of the Rayleigh wave, it is found that higher harmonics are generated, even without any external stress. The second harmonic generation efficiency first increases sharply with the crack depth, and then decreases slightly, when the crack depth reaches around λ/4. The external pressure and friction coefficient of the closed crack are governing parameters that directly change the harmonic generation behavior. The transmission coefficient and second harmonic efficiency can thus be applied as indices for detecting surface closed cracks or the interface pressure.