Defect Detection Of Unidirectional Carbon Fiber Composites Based On Continuous Line Laser Thermal Imaging

Carbon fiber reinforced composites have better physical properties due to the improvement of processing technology.It is widely distributed in many major applications,such as aerospace,automotive,shipbuilding,construction and sports.Composite materials specially used for aero-engines have also emerged because of the rapid development of military enterprises in recent years.Composites have become an indispensable and important part of the composition of aerospace materials.Therefore,it is necessary to use testing technology to evaluate the safety and reliability of material parts at different stages of the manufacturing and maintenance process.The thermal imaging nondestructive testing technique using laser as excitation source has obvious advantages in surface or near surface defect detection and defect parameter list characterization.Laser has the advantages of non-contact,controllability,high sensitivity,and low air loss.It has gradually become one of the important means of detecting material defects because of the existence of these reasons.Laser imaging technology has gradually become a new application field of nondestructive testing.This technology is mainly used in metal defect detection and characterization at home and abroad,but relatively few studies on composite material defects have been conducted.Therefore,this paper mainly focuses on the related research about the surface defect detection technology of unidirectional carbon fiber composites based on continuous line laser thermal imaging.A line laser non-destructive testing system based on reflection is constructed.The main research contents and work arrangement of this paper are as follows:(1)The non-destructive testing technology of infrared thermal imaging is explored,and the significance of using infrared thermal imaging is analyzed in combination with the research topic.The research methods of infrared thermal imaging technology are introduced,including common thermal non-destructive techniques and selection of heating sources.Then follow the research at home and abroad,and expound the current development situation.(2)In order to study the influence of material surface defects on the detection efficiency of line laser scanning thermal imaging,the principles involved in this technology are firstly introduced.Then,based on the finite element software,the thermal conduction simulation analysis of unidirectional carbon fiber surface defect detection was done.Based on the simulation results of the COMSOL platform,temperature and thermal image analysis was done.The experimental results all prove that the defects of carbon fiber material will hinder the diffusion of heat flow during the heating and cooling process of the sample.It is embodied in the obvious temperature difference area on the surface of the material,which provides a theoretical basis for the location of defects.The type,size and depth of the defect can have a significant effect on temperature.The simulation results also provide the basis for the selection of the range of laser parameters for subsequent experiments.(3)In order to solve the problem that the image target ratio is small and affects the detection efficiency,we propose a method to extract the ROI of the region of interest based on the HSV color space.For thermal images with low signal-to-noise ratio,poor contrast,and blurred defect features,we analyze the source of noise and propose a combined algorithm based on filtering and local adaptive contrast enhancement-ACE.The results of the algorithm processing are evaluated,and the results show that the method has a good effect on this kind of problem.(4)For the problem of surface defect feature extraction of carbon fiber reinforced composites,we propose a combined algorithm of image binarization based on improved edge sharpening and edge improved global threshold.We use this algorithm to realize the detection of sequence images or hotspot videos.For the three-dimensional characterization of defects,the principle of convex hull is mainly introduced.We use this principle to realize the minimum outer rectangle of the outline,and complete the specific digitization of defects such as positioning,area size,and damage length.(5)For the detection and experimental verification of carbon fiber surface defects,a nondestructive testing system based on reflection was built to collect the heat map information of the material.The algorithm is used to complete the image segmentation,enhancement and feature extraction effect verification of image sequence or video.Through multiple experiments and image data analysis of defects of different types,sizes,and depths in the specimen,we achieved a 3D characterization of the size,area,and length of surface defects in carbon fiber materials.