Research Of Coplanar Array Capacitive Imaging Testing Technology For A Loose And Porous Thermal Insulation Material

Loose and porous composite material is a common kind of thermal insulation material in spaceflight,which can interdict the heat generated by the friction between aircraft and air transfer into the interior of the aircraft,so thermal insulation material is important to ensure the flight safety.At present,thermal insulation material is usually bonded to the surface of aircraft as a heat insulation structure,but if the bonding quality is not high,the performance of heat insulation must decrease.Therefore,it is very necessary to use non-destructive testing technology to detect defects and evaluate the bonding quality of thermal protection structures.In order to solve this problem,this study uses the loose and porous heat insulation composite material as the research object and the problems of visual detection in the adhesive are emphatically studied.Firstly,a coplanar array capacitive imaging based on capacitance sensing principle is proposed,and the electric field type of the coplanar array electrode,the sensitive mechanism of the capacitance sensor to defects are studied.Based on the finite element method,the three-dimensional model of the capacitance sensor with 12 electrodes.The influences of division method of sensitive field on the sensitivity distribution,the stability of the sensitivity matrix and the quality of the reconstructed image are studied and the optimal division method of the sensitive field is obtained.By comparing the similarity of sensitivity matrixes of sensitive fields in different dielectric constants,the effect of the fluctuation of the dielectric constant caused by environmental factors on the detection results is exploreed.Secondly,the empty field and full field setting method of the ECT system in the experiment is studied.Aiming at the shortcomings of the existing method,an empty field setting method based on the self rotation of the measured field is proposed.With real bonding heat insulation samples as tested object,two methods of differential capacitance value analysis and image reconstruction are used to analyze the measured data,and the feasibility of the method in the actual measurement process is proved.Finally,the detection performance of the 12 electrode array capacitance imagingsystem is explored,and the recognition distance between multiple defects and the resolution of defects of the detection system are obtained according to the experimental results..The mobile measure is preliminary explored to realize large area detection.The change of the capacitance in the mobile process is studied,and the feasibility of the quantitative characterization of the rule defect is analyzed.