Research On Planar Array ECT Applied To Adhesive Laye Defect Detection Of Thermal Insulation Material

The thermal protection material is vital to guarantee the safety of flight vehicle and flight crew. The thermal protection material is usually bonded with flight vehicle by binder. The defects and damage occurred on adhesive layer can result in bonding strength reduction, and once the defects and damage are accumulated to some extent, the thermal protection material may split away from the flight vehicle which will seriously threat the safety of the flight vehicle.To realize reliable detection and evaluation of adhesive layer, a nondestructive testing method is presented based on planar array Electrical Capacitance Tomography(ECT). According to theoretic analysis and simulation analysis, a planar array capacitance sensor is designed and fabricated, and a adhesive layer testing system based on planar array ECT is developed. Then some experimental samples with man-made defects are tested and the image reconstruction results are also processed analyzed. The results show that the defects in adhesive layer can be effectively recognized by the developed planar array ECT system.Firstly, According to analysis of the principle of planar array ECT, combined with the characteristic and special requirements of adhesive layer defect detection, a detecting scheme to realize adhesive layer defect detection using planar array ECT is proposed. The forward problem and inverse problem of planar array ECT are analyzed. The solution and the implementation process for the two problems are given.Secondly, according to requirements of adhesive layer defect detection, a planar array capacitance sensor of 12 electrodes is designed and fabricated by theoretical analysis and simulation analysis. An image reconstruction software based on Mathematica software is programmed. We establish the simulation model of the planar array sensor and acquire the sensitivity matrix which is the key prior information of image reconstruction based on APDL language. Combined with a purchased capacitance acquisition system according to the measurement precision requirement, a complete adhesive layer testing system based on planar array ECT is designed and established.Finally, A series of experimental samples with man-made defects in the adhesive layer are tested by the developed detection system. The reconstructed images of adhesive layer are processed using image segmentation technology and the area of defects is calculated. By comparing the area of reconstructed images and actual defects, the testing effect of the testing system is analyzed. The results show that the defects in adhesive layer can be effectively recognized by developed planar array ECT system. And it also demonstrates the feasibility of adhesive layer defect detection using planar array ECT system.