Xu Caibin, Gao Guangjian, Deng Mingxi
College of Aerospace Engineering, Chongqing University, Chongqing 400044, China.
Department of Physics, Army Logistics Academy, Chongqing 401331, China.
Ultrasonics. 2023 Dec;135:107108. doi: 10.1016/j.ultras.2023.107108. Epub 2023 Jul 17.
Considering a trade-off between temporal-spatial resolution and multi-mode nature of Lamb waves, tone bursts with short durations are usually used as excitations in Lamb wave based damage detection. A short-duration excitation usually requires a large amplitude to carry sufficient energy so as to obtain response signals with enough signal-to-noise ratio and cover a large inspection area. In this paper, an alternative Lamb wave damage imaging method using nonlinear chirp (nonlinear frequency modulation, NLFM) excitation with a long duration and a small amplitude is proposed. The signal processing techniques of pulse compression and dispersion compensation are adopted to compress the long-duration wave packets of response signals into short ones. Compared with conventional tone burst excitations with short durations and small amplitudes, due to the long duration of the nonlinear chirp excitation and the use of pulse compression, sufficient energy can be applied to transducers under small amplitude excitations so the image contrast in imaging will not degrade. Furthermore, as large amplitude excitations are no longer required, high voltage amplifiers are not necessary so the hardware of the Lamb wave testing system is simplified. Experiments on a carbon steel plate with an artificial crack are carried out and Lamb wave signals are collected using a linear array consisting of nine PZTs. Experimental results under the NLFM signal and conventional tone bursts are provided. Experimental results show that under the condition of the same excitation amplitude, the proposed method under the NLFM excitation can achieve better imaging quality compared with methods under conventional tone bursts.
考虑到兰姆波的时空分辨率与多模式特性之间的权衡，通常使用持续时间短的 tone bursts 作为基于兰姆波的损伤检测中的激励信号。短持续时间的激励通常需要较大的幅度来携带足够的能量，以便获得具有足够信噪比的响应信号并覆盖较大的检测区域。本文提出了一种使用长持续时间和小幅度的非线性啁啾（非线性调频，NLFM）激励的兰姆波损伤成像方法。采用脉冲压缩和色散补偿的信号处理技术将响应信号的长持续时间波包压缩为短波包。与传统的短持续时间和小幅度的 tone bursts 激励相比，由于非线性啁啾激励的持续时间长且使用了脉冲压缩，在小幅度激励下可以向换能器施加足够的能量，因此成像中的图像对比度不会降低。此外，由于不再需要大幅度激励，因此不需要高压放大器，从而简化了兰姆波测试系统的硬件。在具有人工裂纹的碳钢平板上进行了实验，并使用由九个压电陶瓷组成的线性阵列采集了兰姆波信号。给出了 NLFM 信号和传统 tone bursts 下的实验结果。实验结果表明，在相同激励幅度的条件下，与传统 tone bursts 下的方法相比，NLFM 激励下的所提方法能够实现更好的成像质量。
