Wang Ruonan, Fang Yang, Gao Qianxiang, Li Yong, Yang Xihan, Chen Zhenmao
State Key Laboratory for Strength and Vibration of Mechanical Structures, Shaanxi Engineering Research Centre of NDT and Structure Integrity Evaluation, School of Aerospace Engineering, Xi'an Jiaotong University, Xi'an 710049, China.
Sensors (Basel). 2023 Jul 24;23(14):6629. doi: 10.3390/s23146629.
Glass fiber-reinforced polymer (GFRP) is widely used in engineering fields involving aerospace, energy, transportation, etc. If internal buried defects occur due to hostile environments during fabrication and practical service, the structural integrity and safety of GFRP structures would be severely undermined. Therefore, it is indispensable to carry out effective quantitative nondestructive testing (NDT) of internal defects buried within GFRP structures. Along with the development of composite materials, microwave NDT is promising in non-intrusive inspection of defects in GFRPs. In this paper, quantitative screening of the subsurface impact damage and air void in a unidirectional GFRP via microwave reflectometry was intensively investigated. The influence of the microwave polarization direction with respect to the GFRP fiber direction on the reflection coefficient was investigated by using the equivalent relative permittivity calculated with theoretical analysis. Following this, a microwave NDT system was built up for further investigation regarding the imaging and quantitative evaluation of buried defects in GFRPs. A direct-wave suppression method based on singular-value decomposition was proposed to obtain high-quality defect images. The defect in-plane area was subsequently assessed via a proposed defect-edge identification method. The simulation and experimental results revealed that (1) the testing sensitivity to buried defects was the highest when the electric-field polarization direction is parallel to the GFRP fiber direction; and (2) the averaged evaluation accuracy regarding the in-plane area of the buried defect reached approximately 90% by applying the microwave reflectometry together with the proposed processing methods.
玻璃纤维增强聚合物（GFRP）广泛应用于航空航天、能源、交通等工程领域。如果在制造和实际使用过程中由于恶劣环境而出现内部埋藏缺陷，GFRP结构的结构完整性和安全性将受到严重损害。因此，对GFRP结构内部埋藏的缺陷进行有效的定量无损检测（NDT）是必不可少的。随着复合材料的发展，微波无损检测在GFRP缺陷的非侵入式检测方面具有广阔前景。本文深入研究了通过微波反射法对单向GFRP中的亚表面冲击损伤和气孔进行定量筛选。利用理论分析计算得到的等效相对介电常数，研究了微波极化方向相对于GFRP纤维方向对反射系数的影响。在此基础上，建立了微波无损检测系统，进一步研究GFRP中埋藏缺陷的成像和定量评估。提出了一种基于奇异值分解的直达波抑制方法，以获得高质量的缺陷图像。随后通过提出的缺陷边缘识别方法评估缺陷的平面内面积。模拟和实验结果表明：（1）当电场极化方向与GFRP纤维方向平行时，对埋藏缺陷的检测灵敏度最高；（2）将微波反射法与所提出的处理方法相结合，对埋藏缺陷平面内面积的平均评估精度达到了约90%。
