Abstract
The principle about the nonlinear ultrasonic mixed frequency is introduced. A novel identification method for incipient structural health prognosis is proposed based on heterolateral co-linear mixed-frequency ultrasound to identify the micro-crack in mechanical structures. The modelling analysis methodology by the application of finite element analysis (FEM) is developed to simulate the nonlinear mixed-frequency ultrasonic wave transmission mechanism from the cracks with different depths and the excited frequency. The correlation models between the crack widths and the mixed-frequency nonlinear coefficients are established. An experimental method based on the nonlinear mixed-frequency ultrasonic theory is proposed to actuate the differential and sum-frequency characteristic mixed waves that interact with the defects of materials, which obtains the nonlinear coefficients to identify the depths of cracks in materials. The FEM model is verified to be effective at predicting the width of the cracks by comparing it with the testing data. The sizes of cracks have a positive correlation with the nonlinear coefficients of the mixed frequencies. A prognosis model for the mixed-frequency nonlinear coefficients is established to predict the crack depths of the specimen.