Development Of Nondestructive Testing System For Adhesive Layer Structure Of Thermal Insulation Material By Planar Electrical Capacitance Tomography

With the research of hypersonic vehicle in many countries,it has gradually become an important development direction in the field of aerospace,and will play an important role in the future national defense security.In the process of flight,considering that the outside of the aircraft will be in a high temperature environment,the thermal insulation layer will be covered on the surface of the aircraft to ensure the safety of the aircraft.Therefore,the quality of adhesive layer structure between thermal insulation materials and aircraft will play a vital role.Considering that there is no good means to detect this target at present,this paper will improve the electrical capacitance tomography technology to detect the defects of the adhesive layer structure.Firstly,by analyzing the principle of electrical capacitance tomography technology,it is applied to the planar electrical capacitance tomography technology to achieve the visual detection of defects in the deeper layer structure of the material.The structure of the sensor is analyzed,and then the parameters of the sensor unit are analyzed by finite element simulation software,and the appropriate sensor structure parameters are finally determined.Afterwards,the sensitive field parameter in electrical capacitance tomography technology is deduced and analyzed,and calculated by simulation software,which is the important basis of final image reconstruction.After that,the whole system structure of sensor measurement is designed,which is mainly divided into two parts: hardware and software.The hardware part includes capacitance measurement,switch between electrodes,and data reading and sending.The software part includes serial communication between computer and single chip computer,data acquisition and storage,data calculation using image reconstruction algorithm,image difference algorithm and image preservation and display.In this way,a whole measurement system can be formed with the designed sensors.Then some image reconstruction algorithms commonly used in electrical capacitance tomography are studied.The normalization of capacitance value in this technology is discussed,and a suitable normalization method is determined.Several defects are simulated and analyzed by using simulation software.Then image reconstruction is carried out by using simulation data.Five algorithms,linear back-projection algorithm,singular value decomposition algorithm,standard Tikihonov regularization algorithm,Landweber iteration method and Newton-Raphson iteration method,are used to calculate the simulation results.The effects of some parameters of these algorithms on the simulation results are analyzed.The Landweber iteration algorithm is improved by introducing the relative capacitance residual index.The iteration times and iteration time of the algorithm are reduced on the basis of guaranteeing the reconstruction quality.Finally,the performance of the test system is briefly analyzed,and the simulated glue layer defects are tested by the developed test system.The feasibility of the planar electrical capacitance tomography technology in the glue layer defects detection is verified,which provides a new development idea for the non-destructive testing in aerospace field.