<p>Aluminum alloy is widely used in various fields because of its advantages such as low density, oxidation resistance and anti-corrosion. Aluminum alloy structures are prone to suffer from fatigue damage caused by alternating loads. The accumulation of fatigue damage can lead to structural failure. Therefore, it is of great engineering significance to detect the early fatigue damage of aluminum alloy structures. At present, most of the traditional non-destructive inspection methods are not sensitive to the early damage of materials, however nonlinear ultrasound testing as a new detection technology with a broad application prospect which can evaluation of material performance degradation of materials from micro level. Therefore, the research on nonlinear ultrasonic testing technology can effectively improve the reliability of in-service mechanical equipment and realize structural health monitoring. As one of the nonlinear ultrasonic testing methods, mixing nonlinear ultrasonic testing technology is sensitive to small damage and can reduce the influence of testing system non-linearity. In this paper, a nonlinear ultrasound mixing method is developed to detect early fatigue damage in aluminum alloy structures. Combining the nonlinear ultrasonic theory with the model of fatigue crack propagation, the propagation and modulation behavior of mixed ultrasonic on the contact surface of closed crack are analyzed. The relationship between the nonlinear response and the cumulative damage degree in the fatigue damage sample is deduced, and the mixing nonlinear ultrasonic detection mechanism of early fatigue damage is revealed. Seven aluminum alloy specimens with different fatigue damage degrees are prepared by fatigue test. An experimental system is designed for performing nonlinear ultrasound mixing detection of fatigue damage in aluminum alloy specimens. Two columns of ultrasonic signals with different frequencies are selected for simultaneous excitation The influence of different excitation parameters on the test results is studied, and the principle of selecting the best excitation parameters is determined. A signal processing method based on time-frequency analysis is proposed to extract modulation characteristics of the ultrasound mixing detection signal. An acoustic nonlinear parameter is defined using the extracted modulation characteristics, in order to evaluate the modulation intensity of two ultrasound signals in the fatigue damage region. The experimental results indicate that the acoustic nonlinear parameter increases monotonically with the degree of fatigue damage, and thus it can be used to quantify fatigue damage. The proposed nonlinear ultrasound mixing method facilitate the detection of fatigue damage and further assessment of the severity of the damage in aluminum alloy structures.</p>

Detection of Fatigue Damage in Aluminum Alloy Structures Using Nonlinear Ultrasonic Modulation

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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