Research On Composite Detection Based On Plane ECT Technology

Compared with other materials,composite materials have higher quality,better corrosion resistance,higher strength and stiffness.Because of its many advantages,composite materials are widely used in aerospace and military industry.In the manufacturing process,composite materials may be affected by process and production environment factors,resulting in defects in the manufacturing process;in the use or service process,impact injury may occur,resulting in cracks,delamination and other defects in the materials;the impact of high temperature and other external factors may cause aging cracking of the materials.Defects may cause the composite to lose its original properties.The material after the performance failure may affect the flight safety of the aircraft and the normal operation of the equipment.So it is very important to detect the defects of composite materials.With its unique advantages,electrical capacitance tomography(ECT)technology has been widely used in the detection of aviation composite materials.Based on the edge effect of capacitance,the technology can detect the location of defects quickly and accurately without damaging the material.Based on the plane ECT technology,this paper explores the structure of plane electrode sensor,designs a biplane ECT signal detection system based on FPGA as the core controller,carries out the feasibility of the improved sensor and carries out the nondestructive testing experiment on the composite materials with structural defects.The article will discuss from the following contents:(1)The optimal design of the plane sensor is carried out.Through several important evaluation indexes of the plane capacitance sensor,the related indexes of the optimized sensor are evaluated.The simulation software COMSOL is used to model the two-sided sensor.The influence of the electrode structure of biplane capacitance sensor,such as length width ratio and spacing,on the detection effect of the sensor is studied.The results show that the sensitivity of the sensor can be improved by reducing the electrode spacing and aspect ratio.Through the simulation experiment,the effect of biplane capacitance sensor on the detection of cracks,bubbles and layered defects is verified,and compared with single-sided sensor.(2)Design and build a set of ECT detection system based on FPGA.The hardware design principle of the system is introduced in detail,and the key circuits such as switch circuit,C / V circuit,a / D circuit and data transmission circuit are described in detail.The generation of excitation signal,phase sensitive demodulation,data transmission program design are explained.(3)Verify the function of the designed plane ECT system.Explore the signal detection intensity of the system,analyze the data curve and test the signal-to-noise ratio parameters of the system.A composite material experiment template with defects is constructed.The cracks and holes are detected by ECT system,and the dielectric constant image is reconstructed by non iterative and iterative algorithm.