Research On Visual Monitoring Technology Of Structural Cracks Growth Based On Alternating Current Field

Aiming at the requirement of long-term fixed-point monitoring of surface cracks at key structural nodes of aerospace equipment,the visual monitoring technology is put forward in this paper based on the alternating current field measurement(ACFM)technique.The alternating current field monitoring sensor arrays and the supporting hardware processing circuits are developed.The cracks growth monitoring visualization and monitoring quantitative methods are set up.The monitoring system software is compiled.And finally an alternating current field monitoring system is built.The experiments are conducted to achieve visual monitoring of structural cracks growth and quantitative crack monitoring.This thesis mainly conducts research from the following four aspects:(1)Simulation analysis of alternating current field monitoringBased on the principle of ACFM,the alternating current field monitoring technology is introduced.The simulation model of alternating current field monitoring is established using COMSOL finite element software.The characteristics of induced current and magnetic field distortion in the surface crack area of the structure are simulated and analyzed.The excitation frequency of the alternating current field monitoring and the arrangement spacing of monitoring sensors are optimized,which provide a theoretical basis for the subsequent design of monitoring sensor array and the research of the crack propagation visualization and the crack quantitative monitoring methods.(2)Development of hardware system for AC electromagnetic field monitoringBased on the optimized sensor spacing,the alternating current field monitoring sensor array is developed.The weak signal conditioning circuit is designed with signal amplification,filtering and AC-DC conversion.Then the signal acquisition module and power amplifier circuit are further integrated to develop the alternating current field monitoring instrument.Finally,the alternating current field monitoring hardware system is built,which provides the hardware foundation for the experiments of alternating current field monitoring.(3)Design of crack growth monitoring method and the softwareThe distribution law of monitoring signal during crack propagation is simulated and analyzed.The method is designed to make the cracks propagation judgment and the propagation type judgment.The cracks endpoint location method is further designed by imitating the centroid solution method,which helps to realize quantitative monitoring of the length and angle of structural surface cracks.Then the quantitative monitoring method of cracks depth is designed.Finally,the software of the alternating current field monitoring system is compiled,which provides the software foundation for the experiments of alternating current field monitoring.(4)Experiments of alternating current field monitoringThe alternating current field monitoring experimental system is built by integrating the alternating current field measurement monitoring software and hardware.Then the monitoring experiments are carried out on the artificial cracks,which including the crack length growth monitoring experiment,the crack depth growth monitoring experiment,the monitoring experiment of cracks at different angles and the crack endpoint propagation monitoring experiment.The experimental results show that the system can realize the visualization and quantitative monitoring of crack growth,which lays a foundation for the industrial application of alternating current field monitoring.