Detection of Delamination in GFRP Laminates Using Electromagnetic Acoustic Transducers

将电磁声换能器（EMATs）应用于玻璃钢（GFRP）层合板的分层检测。由于兰姆波的速度与板厚有关，我们提出通过检测兰姆波速度的分数变化来评估分层。emat由嵌入在层压板中的线圈和放置在层压板上的永磁体组成，用于发射和接收兰姆波。我们测量了相速度和群速度。在群速测量中，用短脉冲激励发射机EMAT。然后，在时域内计算接收信号的中心频率分量的幅值。将峰值振幅的时间与路径长度进行对比，我们可以将分层段评价为斜率稍微降低的区域。我们发现，在12层压板中，分层前沿的位置可以以10mm的精度进行评估。为了测量相速度，我们使用了曲线线圈EMAT。当Lamb波的半波长与线圈螺距重合时，接收信号的幅值达到最大值。我们发现，在32层的层压板中，可以成功地检测到接收位置的分层。

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.