Development Of Surface Crack Angle Quantitativedetection System Based On RACFM Technique

Due to the directional testing of conventional ACFM technology,a rotating alternating current field measurement(RACFM)method and crack angle quantitative detection system are present in this paper.The RACFM is proved by theoretical analysis,simulations modeling and experiments.Based on the distorted electromagnetic field around the crack on the surface of workpiece,an algorithm using for crack angle quantitative is proposed.The RACFM test system with sensors array and high sensitivity is built and the crack angle quantitative detection experiments are carried out.The main works are summarized as follows:(1)Theoretical and simulation models of RACFMAccording to the theory of rotating electromagnetism and ACFM technology,the double-U shape orthogonal structure excitation coils with 90° phase difference alternating currents are present in this paper.The finite element method simulation model of RACFM is built to analyze the distorted electromagnetic field around the crack on the surface of workpiece.The characteristic array signals above the crack are extracted by numerical simulation model.The theoretical and simulation model of RACFM lay the foundation for the angle quantitative and parameter optimization.(2)Parameter optimization and RACFM system developmentBased on the simulation of RACFM,the parameter,such as double-U shaped excitation currents and the lift-off probe,are optimized.According to the distorted region of electromagnetic field around the crack,the space between two detection sensors is defined,which determines the structure of sensors array.The hardware of detection system is developed,including detection probe,binary channels orthogonal signal source,DC stabilized power supply,data acquisition card and other hardware of RACFM.Also an intelligent software is programmed based on LabVIEW and MATLAB,which achieves the signal processing,and characteristic signals visualization.Then the whole detection system is completed.(3)Algorithm of angle quantitative for arbitrary-angle cracks and results analysisAn algorithm of angle quantitative for arbitrary-angle cracks is built based on the results of experiments and simulation.And crack angle quantitative detection experiments are carried out with the system and algorithm built in this paper.The results show that,on one single scan,the RACFM system effectively achieves high detection sensitivity for arbitraryangle cracks on the surface of workpiece,and the RACFM technology overcomes the limitation of directional detection of conventional ACFM.