Nondestructive Evaluation of Delamination in CFRP Laminates Using Electromagnetic Acoustic Transducers

使用电磁声换能器对 CFRP 层压板分层进行无损评估

• 批准号: 16560077
• 负责人: YAMASAKI Tomohiro
• 金额: $ 2.24万
• 依托单位: Osaka City University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2004
• 资助国家: 日本
• 起止时间: 2004 至 2005
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-16560077/
• 关键词: CFRP; Delamination; Nondestructive Evaluation; Lamb Wave; Electromagnetic Acoustic Transducer; Degradation Evaluation

Electromagnetic acoustic transducers (EMATs) were applied to nondestructive evaluation of delamination in CFRP laminates. Since Lamb wave velocity depends on both frequency and plate thickness, the thickness reduction due to delamination results in the velocity change. In this study, the group velocity of Lamb wave in CFRP laminates was measured by the EMATs while introducing delamination stepwise.The EMAT, which consists of a coil and a permanent magnet, launches the Lamb wave using the eddy current, induced in the vicinity of the plate surface, and the static magnetic field. To enable the eddy current to be generated, we used plain-woven carbon prepreg sheets, which were stacked and were cured in an autoclave. To enhance the magnetic field strength, steel block was put below the plate at the opposed position of the transmitter. In spite of these improvements, Lamb wave signal was still obscured by the leakage of the excitation signal. By taking difference of signals obtained applying two opposite magnetic fields for receiver, Lamb wave signal was extracted. The availability of electromagnet in place of permanent magnet was also examined.Lamb wave signals were received and sampled for various path lengths at each stage of delamination. Distribution of amplitude, in the time domain was calculated for each frequency component. Time of amplitude peak was plotted against path length, the slope of which gives the inverse of group velocity. Comparing the group velocities in the sound and delaminated sections, we found that the group velocity increased in the delaminated area, as predicted theoretically. However, the velocity in the sound section differed from that measured before introduction of delamination. It was revealed that the delaminated part may be detected as the area of elevated velocity when the velocity in the sound part is known.

电磁声换能器 (EMAT) 用于 CFRP 层压板分层的无损评估。由于兰姆波速度取决于频率和板厚度，因此分层导致的厚度减少会导致速度变化。在本研究中，通过 EMAT 测量 CFRP 层压板中兰姆波的群速度，同时逐步引入分层。EMAT 由线圈和永磁体组成，利用板表面附近感应的涡流和静磁场发射兰姆波。为了产生涡流，我们使用了平纹碳预浸料片，将其堆叠并在高压釜中固化。为了增强磁场强度，在发射器相对位置的板下方放置了钢块。尽管有这些改进，兰姆波信号仍然因激励信号的泄漏而变得模糊。通过对接收器施加两个相反磁场所获得的信号的差异，提取兰姆波信号。还检查了电磁体代替永磁体的可用性。在分层的每个阶段，对不同路径长度的兰姆波信号进行接收和采样。计算每个频率分量在时域中的幅度分布。振幅峰值时间相对于路径长度绘制，其斜率给出了群速度的倒数。比较声音和分层部分的群速度，我们发现分层区域的群速度增加，正如理论预测的那样。然而，声音部分的速度与引入分层之前测量的速度不同。结果表明，当健全部分的速度已知时，分层部分可以被检测为速度升高的区域。