Abstract: In order to extend engineering application of nonlinear ultrasonic nondestructive testing technique in wave structure, an experimental technique for excitation and reception directly of Rayleigh wave by fixing piezoelectric sensor on the edge of the specimen is presented, this method is verified by simulation of the finite element method(FEM). By using the experimental system and procedure, cumulative effect of nonlinear Rayleigh waves is proved, nonlinearity parameters nearly linear increase with Rayleigh wave propagation distance increasing, which demonstrates the Rayleigh wave nonlinearity parameters are sensitive for the changes of microscopic defects in the materials internal, and the experimental system and procedure are reliable. Finally, the surface fatigue damage of AZ31 magnesium thick plate is detected by nonlinear Rayleigh waves. Although the experimental results have some dispersion, the ultrasonic nonlinearity parameters overall increase apparently with the fatigue cycles increasing, which shows the Rayleigh wave nonlinearity parameters for the thick plate structure fatigue life prediction have potential engineering applications.

Key words: AZ31 magnesium, Fatigue damage, Finite element method, Nonlinear Rayleigh wave