Defect Detection and Analysis of Ceramic Fiber Composites Based on
THz-TDS Technology
PAN Zhao1, LI Zong-liang1, ZHANG Zhen-wei2, WEN Yin-tang1, ZHANG Peng-yang1
1. Key Laboratory of Measurement Technology & Instrument of Hebei Province, School of Electrical Engineering, Yanshan University, Qinhuangdao 066004, China
2. Key Lab of Terahertz Optoelectronics, Ministry of Education, Department of Physics, Capital Normal University, Beijing 100048, China
Abstract：Ceramic fiber composite is a new Porous light material composed of short cut silicon oxide fibers and its binder sintered by high temperature. The microstructure characteristics of materials directly affect their macrostructure and functional characteristics. The porosity of this material ranges between 84% and 95%. The micro pore size is usually less than 100 microns, with a few occasional nanopores. Ceramic fiber composite materials are used in the outer insulation parts of ultra-high sonic aircraft due to their excellent properties such as high-temperature resistance, low density, high specific strength and ablation resistance. However, this type of material may have inclusions, holes or even large-area debonding caused by factors such as the level of manufacturing and assembly process. The particularity of the structure and application scenarios of ceramic fiber composite materials makes conventional non-destructive testing methods ineffective. Terahertz (THz) technology, as an emerging non-destructive testing technology, has great potential in non-destructive testing of this type of material and can complement conventional testing technologies. This paper studied the defect location method of terahertz time-domain signal and terahertz tomography. Based on Terahertz time-domain spectroscopy (THz-TDS) non-destructive testing technology, this paper obtained the data of waveform peaks and phase differences of the time-domain waveforms and compared them with bonding layer defects and intact bonding layer positions in the sample. The deconvolution filtering technology processed the time-domain waveform, and the relationship between the time-domain waveform and the defect characteristics of the adhesive layer was qualitatively analyzed. The existence of the defect was macroscopically judged. By extracting the optical parameters of the ceramic fiber composite material in the terahertz band, the average refractive index of the terahertz band was determined to be 1.002 8, and then the depth and thickness of the bonding layer defects were 18.4 and 0.28 mm, respectively. Compared with the real depth and thickness of preset defects, the accuracy was 92% and 90% respectively. Since the average refractive index extracted by the time-domain signal will cause errors in the analysis of the defect position of the adhesive layer, this paper used the terahertz tomography method to estimate the position of the defect further analyzing the source of terahertz tomography noise and its impact on imaging quality and used bilateral filtering to reduce the noise of tomography. Based on terahertz tomography technology, a position evaluation model was established, and the thickness of the adhesive layer defect was obtained as 0.26 mm. Compared with preset defect thickness, the accuracy rate was 96%. It effectively perfected the defect location form of the terahertz detection technology and realized the high-precision location and characterization of the bonding layer defects of the ceramic fiber composite material component.
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