基于非线性超声调制频谱识别铝合金板材的疲劳裂纹

Identification of fatigue cracks in aluminum alloy plates based on nonlinear ultrasonic modulation spectrum

基于非线性超声调制频谱法,对航空铝合金板材中的疲劳裂纹识别进行研究;以两个不同频率的超声兰姆波为激励信号,依靠超声换能器、波形发生器和激光测振仪等,对含有疲劳裂纹和无损伤的2024-T351铝合金薄板试样进行对比实验;分别采用时域、频域和时频域联合法分析非线性超声波在铝合金薄板试样中传播的响应信号。结果表明:非线性声学特征即调制频谱及三阶谐波可作为识别2024-T351铝合金板材介质中疲劳裂纹的判据,通过对试样表面进行扫描,建立调制频谱的峰值幅度与位移的关系,据此可确定样板中疲劳裂纹的位置和轮廓,这为航空铝合金板材疲劳裂纹的识别提供更多技术支撑。

The identification of fatigue cracks in the aviation aluminum alloy plates based on nonlinear ultrasonic modulation spectrum method was studied.Taking two different frequencies nonlinear Lamb wave as actuators,comparative experiments on two types of 2024-T351 aluminum alloy plate samples,with and without fatigue crack,were performed by using ultrasonic transducer,waveform generator and non-contact laser vibration meter and so on.The ultrasonic response signals during propagation were analyzed by the time domain,frequency domain and time-frequency domain methods,respectively.The results show that the acoustic characteristic of the modulation frequency components and the third harmonics can be used to indicate the presence of fatigue cracks in 2024-T351 aluminum alloy plates.By scanning the cracked plate,a relationship between the modulation frequency peak magnitude and scanning displacement was established,and according to this relationship the fatigue cracks can be located approximately,the crack contour can be obtained,which will provide more technical support for identification fatigue cracks in aviation aluminum alloy plate.