Experimental Analysis Of Glass Fiber Composites Material Defects Inspection Based On Terahertz Spectrum

Owing to excellent properties of glass fiber composites material,it is widely used in various fields.However,during the process of service,various defects can be caused in these samples.To ensure the structure health of glass fiber composites material,a new nondestructive testing technology was required to detect sample defects.In this dissertation,a series of experimental studies were carried out based on the terahertz time-domain spectroscopy technology.The main content includes:(1)The THz-TDS systems was adopted to measure the refractive index and absorption coefficient of the different defects in glass fiber samples.The results show that the refractive index and absorption coefficient of these samples own obvious features.In the range from 0.2 to 1.8THz,the refractive index of the sample first increases then decreases with the increment of the frequency,and the average refractive index of this samples reaches about 1.7736.Also,the absorption peak positions of the defects are different,which mainly focus on the range from 0.8 to1.75 THz,and 4 to 5 obvious absorption peaks are owned by all kinds of defective samples.(2)Thickness of 1mm glass fiber samples,with many kinds of defects,were detected by transmission terahertz spectroscopy imaging system.The results show that,first,the defects can be reflected clearly by the transmission imaging results of hole defects,but the imaging results of scratched defects are different from the actual situation.Besides,the effect of detection defects was obvious for thermal damage,backside metal and surface-adhered aluminum foil samples by reflective terahertz spectroscopy system.However,it was not so clearly by using the terahertz time-domain spectroscopy technology to detest scratches(wear)and hole defects of the samples.(3)In this dissertation,the comparison analysis of terahertz imaging,scanning electron microscopy and DR imaging for the typical defects of glass fiber compositematerials(with 10 mm long,10 mm wide and 1mm high)was discussed.The results show that the DR imaging results are more clear and the defect profiles are more obvious.Meanwhile,the results of scanning electron microscopy can reflect the material composition of the sample as well as the micro-structure of its defects clearly.(4)By using the image enhancement and image segmentation towards the two typical defects of terahertz imaging results and DR imaging results,the situation can be reflected more clearly,compared with the original detection results.