Finite-difference simulation of rayleigh wave scattering at a surface crack with experimental verification

This paper describes a three-dimension finite-difference method to simulate the interaction of surface acoustic waves with finite-size, surface-breaking, and semi-circular cracks in steel specimen. The simulation is used to predict time-domain history of field displacements vertical to the surface of the steel specimen. We focus on the behavior of the reflection and transmission coefficient of the Rayleigh waves from such cracks in the far field of the crack, when the crack depth is comparable to the wavelength of the interrogating surface wave. The theoretical, finite-difference, and experimental results presented are in very good agreement over the range were the crack depth is much smaller or much larger compared to the wavelength of the incident Rayleigh wave. In the transition regime, between these two limiting cases, only the finite-difference and experimental data show good agreement since the theoretical predictions are no longer applicable. Furthermore, based on the finite-difference simulation and the laser interferometric measurement, the transmission coefficient of the surface wave scattering from the small surface crack was presented.