FEM simulation and experimental study of fatigue damage measurement in magnesium using nonlinear ultrasonic

Based on the theory of nonlinear ultrasonic, material early mechanical degradation is associated with the microstructural changes such as dislocation and slip band. When a single sinusoidal ultrasonic wave is launched to a nonlinear medium, the higher harmonics will be generated. A FEM model of nonlinear was established by a special element which account for a nonlinear stress-strain relation. Calculation was performed for the influence of the micro-defect with different length and quantity to ultrasonic nonlinearity parameter. This research develops a robust experimental procedure. There is linear relationship between amplitudes of the second-harmonic waves and the squared fundamental waves as a function of increasing input voltage amplitude. Using this system, ultrasonic nonlinearity parameters of a magnesium sample were measured. The experimental results show that there is a significant increase in nonlinearity parameters linked to fatigue degree; Ultrasonic nonlinearity parameters can characterize the early fatigue damage of magnesium.