Chung Yoonjae, Shrestha Ranjit, Lee Seungju, Kim Wontae
Eco-Sustainable Energy Research Institute, Kongju National University, 1223-24 Cheonan-daero, Seobuk-gu, Cheonan-si 31080, Korea.
Department of Mechanical Engineering, School of Engineering, Kathmandu University, Dhulikhel, Kathmandu 45200, Nepal.
Materials (Basel). 2022 Mar 21;15(6):2333. doi: 10.3390/ma15062333.
The growing use of composite honeycomb structures in several industries including aircraft has demonstrated the need to develop effective and efficient non-destructive evaluation methods. In recent years, active thermography has attracted great interest as a reliable technology for non-destructive testing and evaluation of composite materials due to its advantages of non-contact, non-destructive, full-area coverage, high speed, qualitative, and quantitative testing. However, non-uniform heating, low spatial resolution, and ambient environmental noise make the detection and characterization of defects challenging. Therefore, in this study, lock-in thermography (LIT) was used to detect water ingress into an aircraft composite honeycomb sandwich structure, and the phase signals were binarized through the Otsu algorithm. A square composite honeycomb with dimensions of 210 mm × 210 mm along with 16 different defective areas of various sizes in groups filled with water by 25%, 50%, 75%, and 100% of the cell volume was considered. The sample was excited at multiple modulation frequencies (i.e., 1 Hz to 0.01 Hz). The results were compared in terms of phase contrast and CNR according to the modulation frequency. In addition, the detectability was analyzed by comparing the number of pixels of water ingress in the binarized image and the theoretical calculation.
包括航空航天在内的多个行业对复合蜂窝结构的使用日益增加，这表明需要开发有效且高效的无损评估方法。近年来，主动热成像作为一种可靠的复合材料无损检测与评估技术备受关注，因其具有非接触、无损、全区域覆盖、速度快、定性和定量检测等优点。然而，加热不均匀、空间分辨率低以及环境噪声使得缺陷的检测和表征具有挑战性。因此，在本研究中，采用锁相热成像（LIT）来检测飞机复合蜂窝夹层结构中的进水情况，并通过大津算法对相位信号进行二值化处理。考虑了一个边长为210 mm×210 mm的方形复合蜂窝，以及16个不同尺寸的缺陷区域，这些区域按组分别填充了占单元体积25%、50%、75%和100%的水。在多个调制频率（即1 Hz至0.01 Hz）下对样品进行激励。根据调制频率，对相位对比度和对比度噪声比方面的结果进行了比较。此外，通过比较二值化图像中进水像素的数量与理论计算结果，分析了可检测性。
