| For the structural health monitoring and evaluation of the large-scale metal equipment,the traditional serpentine scanning detection approach is adopted,which is time-consuming and laborious.Therefore,an efficient and timely non-destructive testing approach is necessary to realize the defect evaluation of the large-scale metal components.Pulse eddy current array detection is a new branch of traditional eddy current testing approaches.Through array probe design and multi-channel signal processing,the detection time can be greatly shortened while the defect detection accuracy can be ensured.The array non-destructive testing system can fully utilize the advantages of array detection and promote its application in the industrial field by means of magnetic sensing technology and electromagnetic imaging technology.Due to the high requirements of multi-channel signal processing and the difficulty in extracting feature signals of defect,most of the related research is based on the traditional eddy current detection approach,which can realize the qualitative detection of defects,but the mutual inductance of the coils makes the accuracy of quantitative defection of defects unsatisfied.In order to solve these problems in array eddy current quantitative detection,this paper systematically investigates the pulse eddy current array detection approach based on hall magnetic sensor.The main research work is summarized as follows:(1)Array probe is designed based on magnetic field distribution.The influence of the geometric parameters of the coil and the material of the sample on the magnetic field of the probe unit is studied,the concept of magnetic field inhomogeneity is introduced to futher study the magnetic flux distribution within the inner diameter area of coil,which is concentrated the changing magnetic field caused by defects.The specific dimensions of the coil are determined by considering the the precision of the manufacturing process and the physical size of the magnetic sensor.Then,this thesis analyzes the influence of the excitation signal and the distance between the coils on the magnetic field coupling in the array minimum probe unit model,and set the appropriate distance between the coils.Finally,the arrangement of the probe is appropriately set according to the structural characteristics of the sample.(2)Quantitative detection approach for different types of defects is proposed based on pulsed eddy current testing.The rectangular fatigue defects and circular cylindrical corrosion defects are investigated in this section.The differential peaks at different scanning positions are used as the defect characteristic signals to realize the quantitative detection of the defect width.Then,the corresponding inversion calculation model of differential peak characteristic signal and defect depth is established to realize the quantitative detection for defect depths,of which the defect depth detection error is within 10%.Finally,the electromagnetic imaging for defects is realized by Matlab,and the spatial position of the defect is obtained by the difference of imaging color in different regions.(3)Pulse eddy current array sensing system is set up and some experiment are carried out.The hardware and software platform of the experimental system is built,and the electric motion platform is used to adjust the detection precision of the experimental system.After the experimental data acquisition is completed,the differential peak characteristic signal is extracted by the signal offline processing method,and the detection result is output and saved as a text file to realize the qualitative and quantitative defection of defects.Based on the exerimental setup,some experiments are carried out,and the simulation results are validated. |
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