Study On Multi-layer Layer Fiber Structure And Defect Detection Of Carbon Fiber Composites

Carbon fiber composite material have high strength to weight ratio,great thermal stability,which are widely used in the aerospace,military,cars,and many other engineering fields.In the process of production and during its serving life,various defects will be caused such as delamination,debonding and crack,which can reduce the performance of composite materials and pose a safety hazard.Therefore,it is necessary to study and develop the nondestructive testing technology which can accurately detect the defects in carbon fiber composite materials,and eliminate the risk before the accident to ensure the reliability and safety of the components.This paper investgaes layered fiber structure and defects of carbon fiber composite materials usingeddy current pulsed thermography,and study the characterization of layered fiber structure and the detection of the feature extraction of defective carbon fiber material.The main contents are as follows:(1)The detection and study of the layer fiber structure of carbon fiber multilayer composite materials are based on eddy current pulsed thermography.The fiber orientation of carbon fiber composite materials is complex and diverse,which brings difficulties to the detection of layer fiber structure.Eddy current Pulsed thermography technology was applied by means of electromagnetic excitation as a heating source,using the infrared thermal cameraobservation and analysis of the specimen surface temperature field changes to achieve the goal of detection and feature extraction,the detection method does not require the coupling agent,has the advantages of high detection efficiency and results directly.In this paper,the internal fiber structure information was extracted by using the difference of the direction velocity of carbon fiber heat propagation in the inner layer and Section principal component analysis,and the feasibility of extracting fiber signal from carbon fiber composite materials with different layer fiber structures is tested.In view of the fuzzy phenomenon of the extracted carbon fiber signal,the algorithm of using thermal fuzzy correction is proposed,first to deal with the image,and then to extract the feature based on the principal component analysis.The experimental results show that the thermal fuzzy correction algorithm can suppress the thermal blurring caused by thermal diffusion in the image sequence,and effectively improve the extracted carbon fiber signal characteristics.(2)Research on the internal defects of carbon fiber composite materials based on eddy current pulsed thermography.For the internal defects in the composite material,using electromagnetic excitation to heat the specimen,surface thermal distribution is captured to character defects through the surface thermal spatial-transient distribution caused by internal defects.Principal component analysis is used to study the direction characteristics of the fiber.Then using fast Fourier transform method to deal with the original data,transform the time domain information to the frequency domain and facilitate the extraction of feature information,thus realizing the extraction of carbon fiber direction information.