Non-destructive Testing Research Of CFRP Airfoil Defects Based On Lock-in Infrared Thermography

As the main material for aircraft airfoils,carbon fiber reinforced plastic(CFRP)may produce some defects which includes delamination and debonding due to the difference of the materials and control of process factors.At present,the research on traditional non-destructive testing(NDT)is relatively lagging,which affects the continued development of CFRP in the aviation field.Compared with the traditional NDT method,lock-in infrared non-destructive testing has some advantages,it not only can’t contact the samples,but also has high efficiency.Therefore,infrared non-destructive testing has become the best choice for the NDT of airfoil defects in this paper.In view of the current situation which in the quantitative research of CFRP airfoild efects,this research takes the CFRP which contains bulit-in Teflon as the object.In order to determine the heat source loading parameters of the NDT system,a three-dimensional thermal conduction model was constructed and the specimen is loaded with sinusoidal periodic excitation.Through the simulation results,this research analyzes the distribution of surface temperatur e field in the specimen defective area and sound area under different conditions of defect size,defect depth,heat source loading frequency and material properties.On this basis,the influence of defect size and depth on the optimal detection frequency a nd the best detection time is studyed.These provides a valuable reference for subsequent experiments.Based on the above research,this paper completes the lock-in infrared NDT platform and optimizes the parameters of the infrared camera.After comprehensive evaluation of various filtering methods,the Gaussian filter is used to preprocess the infrared thermal wave image sequence.The defect features information of specimen is extracted by three image sequence algorithms which includes multi-frame accumulation average and difference method,fast Fourier transformation method and principal component analysis method.According to the results of infrared thermal wave image sequence processing,this research realizes the visualization of defects by image post-processing methods,such as image segmentation,phase shift method and grayscale 3D reconstruction.After calibration of the infrared camera,the numerical analysis methods such as extreme value and derivative are used to determine the position and size of the defects.Ultrasonic C-scanning is used to assist in verifying the accuracy of the results and analyze the causes of the errors.Then the quantitative research of the defects is finally realized.In order to verify the research results,the experiments of CFRP samples with built-in Teflon defects and flat-bottom defects are carried out at the end of this research.Based on the infrared thermal wave image sequence processing,the visualization and quantitative estimation analysis of the defects are comple ted.These experiments achieve good results and they show that the infrared NDT platform has high reliability,and the image sequence algorithm adopts in this research has high accuracy.The infrared NDT technology based on lock-in technology has a good effect on the visualization and quantification of defects in CFRP airfoil.