Research On Terahertz Spectroscopy And Imaging Of Defects In CFRP

Carbon fiber reinforced polymers(CFRP)have been widely applied in the aerospace field due to their high specific strength,strong corrosion resistance,and strong plasticity.For civil aircraft composite materials,various factors during their manufacturing,usage,and maintenance processes can result in different types of defects,posing safety risks to aircraft flights.However,internal defects and small-scale flaws are difficult to detect through surface observation alone.In contrast,terahertz non-destructive testing technology offers benefits such as rich spectral information and high penetration capability.It enables visual and quantitative detection of these defects,mitigating safety hazards and ensuring the safety of civil aircraft flights.This thesis focuses on the study of two types of defects in CFRP: pre-existing internal defects and microcracks.The defects are modeled and simulated using COMSOL Multiphysics simulation software,and the defects are then experimentally verified and detected using terahertz non-destructive testing technology.The study aims to explore the relationship between terahertz spectral and imaging information and defect factors.The results indicate that for preexisting internal defects,the reflective terahertz imaging technique can effectively identify the defects within the frequency range of 0.25 THz to 2.50 THz.The temporal imaging time,frequency domain imaging frequency,terahertz reflectivity,temporal spectral amplitude,and power spectral density show a negative correlation with the depth of inherent defects(0.225 mm to 0.900 mm).The imaging frequency of the absorption coefficient,terahertz absorption rate,temporal spectral time delay,and absorption coefficient exhibit a positive correlation with the depth of the defects.For microcracks,they can be effectively identified within the frequency range of 0.2 THz to 2.0 THz.The terahertz reflectivity,temporal spectral amplitude,and power spectral density show a negative correlation with the geometric parameters of the microcracks(length,width,and position).The terahertz absorption rate and absorption coefficient show a positive correlation with these geometric parameters,while the temporal spectral time delay only shows a positive correlation with the position of the microcracks.In summary,based on the linear relationship between terahertz spectra and imaging information and defect geometric parameters,it is possible to predict the geometric information of defects.This enables the visualization and quantitative detection of defects,providing a reference for practical applications in the detection of defects in CFRP.