基于THz-TDS的陶瓷纤维复合材料缺陷检测分析

Defect Detection and Analysis of Ceramic Fiber Composites Based on THz-TDS Technology

新型陶瓷纤维复合材料由短切氧化硅纤维及其胶合物经高温烧结得到的一种轻质多孔材料,材料微观结构特性直接影响着宏观结构特性和功能特性。该类材料的孔隙度分布在84%~95%之间,微观孔径主要集中在100μm范围内,偶尔有少量纳米孔。陶瓷纤维复合材料以其耐高温、低密度、高比强和抗烧蚀等优异性能在超高声速飞行器外层隔热部件得到应用,但该类材料可能因为制作和装配的工艺水平等因素出现夹杂、孔洞甚至大面积脱粘等现象。由于陶瓷纤维复合材料结构与应用场景的特殊性使得常规的无损检测手段效果不佳,而太赫兹(THz)技术作为一种新兴的无损检测技术,在该类材料的无损检测具有很大的潜力,可与常规检测技术形成互补。针对陶瓷纤维复合材料构件粘接层缺陷检测问题,研究了太赫兹时域信号和太赫兹层析成像方式对缺陷定位方法。基于太赫兹时域光谱(THz-TDS)无损检测技术获取和对比试样中有粘接层缺陷和粘接层完好位置的时域波形的波形峰值和相位差异,并经过反卷积滤波技术对时域波形进行处理,定性分析时域波形与粘接层缺陷特性的关系,宏观判断缺陷存在;通过对太赫兹波段陶瓷纤维复合材料光学参数提取测定太赫兹波段的平均折射率为1.028,进而分析粘接层缺陷的深度和厚度分别为18.4和0.28mm,与预置缺陷真实深度和厚度相比准确度分别为92%和90%。但由于通过时域信号提取的平均折射率会给粘接层缺陷位置分析造成误差,因此以太赫兹层析成像方式进一步估计缺陷的位置,分析了太赫兹层析成像噪声来源以及对成像质量的影响并采用了双边滤波对层析成像降噪滤波,基于太赫兹层析成像技术建立了位置评估模型,获取了粘接层缺陷的厚度为0.26mm,较预置缺陷厚度的准确度为96%,有效地完善了太赫兹检测技术对缺陷定位的形式,实现了陶瓷纤维复合材料构件的粘接层缺陷的高精度定位表征。

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 1.0028,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.