Numerical simulation of laser-generated Rayleigh wave pulses propagation in the machined surface with residual stress using finite-difference method

Laser-excited broadband Rayleigh wave propagation behaviors can be used for characterizing material surface characteristics non-destructively. The present paper is concerned with the Rayleigh wave propagation in the machined surface with a damaged layer with residual stress. Biot's theory of small deformations affected by initial stress forms the basis for this study. Taking ground silicon wafer as an example, we adopted a staggered finite-difference (FD) scheme for numerical simulation. By comparing the dispersion images with the theoretical dispersion curves of Rayleigh wave, the accuracy of the FD algorithm is verified. Then, some two-layer models without or with residual compressive stress are utilized to further analyze the dispersion energy characteristics of Rayleigh waves in the machined surface. The results indicate that damage layer thickness and damage degree determine the main Rayleigh wave high-order mode and the energy of the high-order mode, respectively. In addition, residual compressive stress can reduce the phase velocity of the Rayleigh wave to a small extent. Meanwhile it can significantly increase the total energy of the Rayleigh wave which excited by the same excitation source. This paper will provide a valuable reference for laser ultrasonic evaluation of residual stress on the machined surface.