基于非线性电磁超声表面波混频方法的金属疲劳裂纹检测

In view of the difficulty in fatigue damage detection of aluminum alloy plates, the modulation model of electromagnetic ultrasonic surface waves mixing with fatigue crack interface force model was constructed, and the modulation effect of nonlinear surface wave mixing under different excitation frequencies was studied. Thus, the excitation frequency was determined. The propagation of electromagnetic ultrasonic surface wave of aluminum plate and the effect of different crack depth and length of nonlinear mixing was analyzed. At last, the experiment of non-linear ultrasonic surface waves mixing was carried out, and the non-linear characteristics of intact and fatigue specimens were compared and analyzed. The variation in the side frequency component with the frequency, amplitude, signal delay and crack length was studied, and the corresponding relationship curve was obtained according to the relationship between the side frequency component and micro crack length. The experimental results show that when fatigue cracks appear in the aluminum plate, there will be side frequency modulation component; when the two mixing signals reach the fatigue cracks at the same time, the nonlinear modulation effect is the strongest; by fitting the relationship curve between the side frequency component and the length of the micro crack, the crack growth can be effectively monitored, which lays a good foundation for further quantitative detection of metal fatigue crack life prediction.