Detection of Delamination in GFRP Laminates Using Electromagnetic Acoustic Transducers

将电磁声传感器应用于玻璃纤维增强塑料（GFRP）层合板的分层检测。由于兰姆波的速度显示依赖于板的厚度，我们提出了评估分层通过检测兰姆波速度的分数变化。EMAT，其中每一个包括一个线圈嵌入层压板和一个永久磁铁放在层压板上，被用来发射和接收兰姆波。在群速度测量中，采用短脉冲激励发射机电磁超声换能器。然后，在时域中计算接收信号的中心频率分量的幅度。将峰值振幅的时间与路径长度作图，我们可以将分层部分作为斜率略微降低的区域进行评估。在12层板中，我们发现分层前沿的位置可以精确到10mm。为了测量相速度，我们使用了曲折线线圈EMAT。当兰姆波的半波长与线圈节距一致时，接收信号的幅度取最大值。我们发现，在接收位置的分层可以成功地检测在32层的层压板。

Electromagnetic acoustic transducers(EMATs) were applied to detection of delamination in glass fiber reinforced plastic(GFRP) laminates. Since velocity of Lamb wave shows the dependence on the plate thickness, we proposed to evaluate the delamination by detecting the fractional change in the Lamb wave velocity. The EMATs, each of which consists of a coil embedded in the laminate and a permanent magnet put on the laminate, were used to launch and receive the Lamb wave. We measured both phase and group velocities.In the group velocity measurement, short pulse excited the transmitter EMAT. Then, the amplitude of the center frequency component of the received signal was calculated in the time domain. Time of the peak amplitude was plotted against the path length, and we could evaluate the delaminated section as the region of the slightly lowered slope. We found that the position of the Delamination front can be evaluated with an accuracy of 10mm in the 12 ply laminate.In order to measure the phase velocity, we used the meander line coil EMAT. When the half wavelength of the Lamb wave coincides with the coil pitch, the amplitude of the received signal takes the maximum value. We revealed that the delamination at the receiving position can be detected successfully in the 32 ply laminate.