疲劳微裂纹的非线性兰姆波静态分量检测研究

Nonlinear Lamb wave static component method for fatigue microcracks detection

为定量表征板状金属结构中的疲劳微裂纹扩展状态,采用非线性超声兰姆波静态分量方法,对含不同长度疲劳微裂纹的金属结构进行检测。实验采用低频超声换能器间接接收非线性兰姆波静态分量信号并进行时频域分析,获得非线性参数随微裂纹长度的变化趋势,并分析不同模式基频兰姆波生成的静态分量对疲劳微裂纹的敏感性。通过仿真模拟进一步分析非线性兰姆波静态分量的生成机制。结果表明:微裂纹的张开和闭合对兰姆波起调制作用,引起静态分量的生成;非线性参数随疲劳微裂纹扩展单调增加,S3和S1模式基频兰姆波生成静态分量的非线性参数分别增长到313%和201%;S3模式基频兰姆波生成的静态分量对疲劳微裂纹扩展相比S1模式更加敏感。该研究可证明采用非线性兰姆波静态分量方法检测金属结构疲劳微裂纹的有效性。

To quantitatively characterize the fatigue microcrack propagation in metal structures,a nonlinear Lamb wave method is presented to detect specimens with fatigue microcracks using the static component.A low frequency ultrasonic transducer was used to indirectly receive the static component signals.Timefrequency domain analyses were carried out to obtain the nonlinear ultrasonic parameter for microcracks with various lengths.The sensitivity of static components to fatigue microcrack was then analyzed for two fundamental Lamb modes.Finite element simulations were further performed to investigate the generation mechanism of static components.The results show that the static component could be effectively generated due to the modulation of the opening and closing process of the microcracks.With the propagation of fatigue microcracks,the nonlinear ultrasonic parameter increases monotonically to 313% and 201% for the fundamental S3 and S1 modes,respectively,which illustrates that the static component generated by the fundamental S3 mode is more sensitive to fatigue microcrack than the fundamental S1 mode.This investigation demonstrated the effectiveness of the static component-based method for detecting fatigue microcracks in metal structures.