Research On Three-dimensional Visualization Of Defects Based On ACFM

Defect visualization and shape reconstruction have been the hotspot and technical difficulties in the field of electromagnetic nondestructive testing.In this paper,based on the principle of ACFM,3D visualization of defect is reserched by setting up space triaxial ACFM detection model and developing defective visualization system with array sensor.At first,a simulation database of defects which have various types and sizes is built using the optimized spatial triaxial electromagnetic field detection model.The relationship between spatial magnetic field and defect size,angle and surface profile is studied,and the three-dimensional contour reconstruction and visualization algorithms are developed.At the same time,ACFM high precision array probe and space magnetic field signal imaging and defect visualization software are developed to build the ACFM defect visualization system.Performance test and defect 3D contour algorithm validation experiment are carrued out.The results show that the system can detect the micro-crack with a high accuracy using the real-time imaging of the magnetic field,and the three-dimensional contour reconstruction of the defect is realized more accurately through the established visualization algorithm.The paper mainly studies from the following four aspects:(1)Research on ACFM three-axis electromagnetic field theory and simulation modelBased on ACFM detection principle and theoretical model,a simulation model of space triaxial electromagnetic field is established.The model is optimized for core size,probe lift height and excitation frequency.The distribution law of three-axis magnetic field is studied.(2)Establishment of database of defects which have various types and sizes and study of space magnetic field signalBased on the optimized simulation model,the defects of different types and sizes are simulated respectively,and the database of size and spatial three-axis magnetic field are established.Based on the simulation database,the relationship between spatial magnetic field and defect characteristics(size,angle and surface profile)is studied.The gradient fusion method and neural network method are used to invert the defect features,and finally the three-dimensional contour reconstruction method is developed.(3)Development of ACFM detective visualization system with sensors arrayConsidering the sensitivity and resolution of the signal acquisition,the appropriate magnetic sensor is selected and the height,spacing,quantity and arrangement of the sensor are determined.The signal conditioning circuit and the shell are designed to assemble the array probe for space magnetic field signal acquisition.Based on the array probe,a supporting software is developed to achieve real-time magnetic field signal imaging and analysising,and to complete the three-dimensional contour reconstruction of the defect.(4)Tests of ACFM defective visualization systemBased on array probe and software,the ACFM defect visualization system is developed.The software is debugged and the hardware equipment is improved by testing the system's function.In this paper,the rectangular groove size inversion and the reconstruction of the corrosion profile of the corrosion pits are carried out to verify the established three-dimensional contour reconstruction method.