应用非线性Lamb波识别三维铝板中的微裂纹方向的研究

针对结构中不同裂纹方向的检测问题,采用数值模拟的方法,通过有限元软件ABAQUS建立了一种包含人工粘弹性吸收边界的三维铝板模型,对Lamb波S0模态信号与微裂纹的非线性关系进行研究。在该模型中,将三维埋藏微裂纹嵌入到模型内部的固定位置,在相同激励条件下改变裂纹方向并对仿真获得的时域信号进行频谱分析,然后对不同裂纹方向的二次谐波与基波信号的幅值比指向性图的变化规律进行了比较和讨论。仿真结果表明,不同方向的裂纹对Lamb波在裂纹区的散射场分布有明显的影响,波的传播路径满足反射定律,且前向散射信号的幅值比普遍大于后向散射的幅值比。加上人工吸收边界后,前向散射与后向散射的幅值比差值随着裂纹方向角度的增大而增大。检测结果表明,该方法可以在误差允许范围内对任意裂纹方向的角度进行识别。

Research on the application of nonlinear Lamb wave to identifying the directions of micro-cracks in three-dimensional aluminum plate

Crack direction recognition is an important part of structural quality monitoring. To solve the problem of detecting different directions of the micro-cracks buried in three-dimensional thin plate structures, a method of numerical simulation is adopted. An improved three-dimensional aluminum plate model including artificial viscoelastic absorbing boundary is established by finite element software ABAQUS. The nonlinear interaction between the S0 mode Lamb wave and the buried micro-crack is investigated. The buried micro-crack is embedded at a fixed position in the plate model. Different micro-crack directions under the same excitation condition are simulated. Fourier frequency spectral analysis is applied to the received signals. Then, the directivity diagrams of the amplitude-ratio of second harmonic to fundamental wave in different crack directions are compared and discussed. Simulation results indicate that cracks in different directions have a distinct effect on the distribution of Lamb wave scattering field in the crack zone; The wave propagation path satisfies the reflection law, and the amplitude ratio of forward-scattering signal is generally larger than that of the back-scattering signal; The artificial absorption boundary can minimize the influence of the reflected wave, and the energies of the fundamental frequency and second harmonic signals become more concentrated and stable; Meanwhile, the amplitude ratio difference between forward-scattering and back-scattering increases with the increase of crack direction angle. The detection results show that the method can identify any crack direction angle within the allowable error range.