Research of Depth Evaluation for the Simulated Surface Crack Using Rayleigh Waves

This paper provides some simulated surface cracks whose shape, size and extension mode are very close to the real cracks to study the validity of the method of using surface waves to evaluate the crack depth. The reflection and transmission coefficients of Rayleigh waves at cracks with different depths were obtained by using finite element method (FEM). Experiments were performed at a specimen with 8 simulated surface cracks and three couples of EMAT were employed. It shows that the measured transmission coefficients are virtually consistent with the FEM results, while the measured reflection coefficients are obviously smaller than the FEM results, and the difference is positively correlated with the frequency of Rayleigh waves. As a consequence, the depths of the simulated cracks were evaluated by comparing the measured transmission coefficients with the FEM obtained reference curves. At last, a crack depth quantitative detection method based on arrival time difference between low-frequency transmitted wave and delay transmitted wave is proposed.