Research on Nonlinear Ultrasonic Testing Technology of Microcracks in Metallic Materials

The fatigue micro-cracks produced by metal materials in the process of long-term tensile, compression or alternating loads can induce major safety accidents. Therefore, it is necessary to carry out research on early fatigue crack damage detection methods in metal structures. Due to the non-linear acoustic response of cracked materials, the detection of early microcracks in the structure can be achieved based on the changes of other frequency components in the non-excitation bandwidth of the detection signal. This paper takes 6061 aluminum alloy plate as the research object, then uses COMSOL finite element simulation software to simulate the propagation of surface waves in uncracked and cracked samples, and observe the nonlinear response waveforms. Then we set up an ultrasonic nonlinear detection platform, excite the pulse signal modulated by the Hanning window, and calculate the relative nonlinear coefficient corresponding to the second harmonic signal by analyzing the frequency domain waveform of the response signal, so as to verify the nonlinear acoustic response characteristics of the cracked material.