Research On Microwave Thermography Nondestructive Testing Method For Debonding Defect In Radar Absorbing Material Coating

The multi-layer structure system composed of carbon fiber reinforced plastics(CFRP)and radar absorbing material(RAM)has been paid more attention and applied in the field of nondestructive testing(NDT),especially in the field of fighter stealth materials.Debonding defect(DD)is a common defect in this multi-layer structure,especially the debonding damage of multi-layer heterogeneous RAM.Due to the particularity of its location and the thickness limitation of stealth materials,it is difficult to detect and not easy to be found.In order to evaluate the performance of RAM,it is urgent to develop a method to detect and identify the debonding defects of RAM.In view of the characteristic of absorbing electromagnetic wave into heat and the eddy current effect caused by the conductivity of CFRP substrate,active m i cro w av e t h erm o gr ap h y(A M T)is used to detect the debonding defect of this multilayer structure.The main work of this thesis is as follows:Firstly,starting from the theoretical basis of microwave heating,this paper introduces the law of infrared radiation,including infrared spectrum analysis and derivation of the law of infrared radiation,and analyzes the two principles of microwave heating RAM and CFRP.Secondly,the debonding defect of RAM is simulated by COMSOL finite element method under microwave excitation.Based on the debonding between real RAM and CFRP,the AMT simulation model is established to evaluate the microwave heating effect of two industrial microwave frequencies;The ability of AMT to detect the same debonding defects covered by RAM with different thickness is analyzed;The detection rate of debonding defects of various RAM with the same diameter and depth under the same microwave heating condition under the same thickness of RAM coverage is analyzed;The influence of three microwave heating powers on the detection effect is analyzed,and the mechanism of AMT is deeply studied.Then AMT is used to detect the debonding defects of real multilayer structures,and a resonant cavity microwave thermography detection system is developed,which is composed of resonant cavity microwave source,infrared thermal imager,fan and control computer.Through three traditional algorithms,the surface temperature data of RAM collected by thermal imager are processed,and the feature extraction effects of the three algorithms are evaluated.The experimental results show that the system can detect and locate the debonding pixel level of multi-layer heterogeneous RAM,and verify the high performance of the system.Finally,by analyzing the thermal time and thermal space characteristics of the experimental data,the original experimental data collected by the thermal imager are calibrated,and the one-dimensional temperature time series data set is established.The one-dimensional convolutional neural network is used to train and predict the data set,so as to realize the intelligent detection of AMT.