Detection of Delamination in GFRP Laminates Using Electromagnetic Acoustic Transducers

将电磁声换能器(EMAT)应用于玻璃纤维增强塑料(GFRP)层合板的分层检测。由于Lamb波的速度与板厚有关，我们建议通过检测Lamb波速度的分数变化来评估分层。EMAT中的每一个都由嵌入在层压板中的线圈和放置在层压板上的永久磁铁组成，用于发射和接收兰姆波。我们测量了相速度和群速度。在群速度测量中，短脉冲激励发射机EMAT。然后，在时间域中计算接收信号的中心频率分量的幅度。波幅峰值的时间与路径长度的关系图，我们可以将分层截面作为略微降低的斜率区域。结果表明，在12层复合材料层合板中，分层前沿位置的测量精度可以达到10 mm，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重合时，接收信号的幅度取最大值。我们发现，在32层叠层板中，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.