Abstract:

Due to the influences of stress, impact and cyclic load, metal structure was likely to generate fatigue crack or other tiny damages. Conventional nonlinear modulation method could not detect fatigue crack when the boundary conditions were nonlinear. Herein, a nonlinear ultrasonic modulation method was developed to detect a fatigue crack on an aluminum beam,which recognized the modulation of tone burst and high-frequency ultrasonic wave. Intact beam and cracked beam were chosen as the subjects for the experiments, two PZTs were boned on the surface of the aluminum beams as the actuator and the sensor.The STFT was used for computing the spectrograms of the response which is acquired by the sensor. The modulations of tone burst and continuous sinusoidal excitation indicate the presence of fatigue crack.

Key words: fatigue crack, structural health monitoring, boundary nonlinearity, nonlinear ultrasonic modulation, short-time Fourier transform(STFT)

摘要：

由于应力作用、撞击以及周期载荷等因素的影响，金属结构中不可避免地产生疲劳裂纹损伤。若结构存在边界非线性，传统的非线性调制方法将无法有效识别疲劳裂纹损伤。针对该问题，提出一种能够避免边界非线性干扰的非线性超声调制方法。该方法采用正弦脉冲信号和持续正弦信号作为激励，通过识别信号之间的非线性调制现象来进行损伤检测。分别以铝制裂纹梁和完整梁为实验对象，粘贴两个压电片作为作动器和传感器，利用短时傅里叶变换对响应信号进行时频分析，提取非线性调制信号成分，对疲劳裂纹损伤进行有效的识别。

关键词: 疲劳裂纹, 结构健康监测, 边界非线性, 非线性超声调制, 短时傅里叶变换