Skin depth and detection ability of magneto-optical imaging for weld defects in alternating magnetic field

2020 ◽  
Vol 55 ◽  
pp. 44-55
Author(s):  
Xiangdong Gao ◽  
Xiaohu Zhou ◽  
Congyi Wang ◽  
Nvjie Ma ◽  
Yanxi Zhang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Optical Imaging ◽  
Skin Depth ◽  
Alternating Magnetic Field ◽  
Detection Ability ◽  
Weld Defects

A novel detection of weld defects by magneto-optical imaging under combined magnetic field

2021 ◽  
Vol 63 (12) ◽  
pp. 704-711
Author(s):  
Nvjie Ma ◽  
Xiangdong Gao ◽  
Congyi Wang ◽  
Yanxi Zhang
Keyword(s):  
Magnetic Field ◽  
Standard Deviation ◽  
Optical Imaging ◽  
Alternating Magnetic Field ◽  
Contour Extraction ◽  
Weld Defects ◽  
Optical Images ◽  
Weld Defect ◽  
Shaped Crack ◽  
Magnetic Field Imaging

To overcome the shortcomings of existing magneto-optical imaging, such as the saturation of an image under a constant magnetic field and the ambiguity of an image under an alternating magnetic field, imaging using a combined magnetic field is presented in this research. Weld defect samples include a laser-cut groove, a wire-cut penetrating groove, a pit and a Z-shaped crack. Magneto-optical imaging experiments were carried out under different magnetic fields. Contour extraction and standard deviation calculations were carried out for all magneto-optical images and the maximum standard deviation of the laser-cut groove under an alternating magnetic field was 20.9, which was less than the maximum value of 37.4 under a combined magnetic field. The experimental results show that the contrast of a magneto-optical image obtained under the combined magnetic field is greater than that obtained under the alternating magnetic field for all defects. The proposed combined magnetic field could optimise the magneto-optical imaging effect for weld defects under the existing excitation method to a certain extent.

Detection model of invisible weld defects by magneto-optical imaging at rotating magnetic field directions

2020 ◽  
Vol 121 ◽  
pp. 105772 ◽  
Author(s):  
Yanfeng Li ◽  
Xiangdong Gao ◽  
Yanxi Zhang ◽  
Deyong You ◽  
Nanfeng Zhang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Optical Imaging ◽  
Rotating Magnetic Field ◽  
Weld Defects ◽  
Detection Model

Weld cracks nondestructive testing based on magneto-optical imaging under alternating magnetic field excitation

2019 ◽  
Vol 285 ◽  
pp. 289-299 ◽  
Author(s):  
Yanfeng Li ◽  
Xiangdong Gao ◽  
Qiaoqiao Zheng ◽  
Perry P. Gao ◽  
Nanfeng Zhang
Keyword(s):  
Magnetic Field ◽  
Nondestructive Testing ◽  
Optical Imaging ◽  
Alternating Magnetic Field ◽  
Field Excitation

Magneto-optical imaging characteristics of weld defects under alternating and rotating magnetic field excitation

2019 ◽  
Vol 112 ◽  
pp. 188-197 ◽  
Author(s):  
Xiangdong Gao ◽  
Liangliang Du ◽  
Nvjie Ma ◽  
Xiaohu Zhou ◽  
Congyi Wang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Optical Imaging ◽  
Rotating Magnetic Field ◽  
Weld Defects ◽  
Imaging Characteristics ◽  
Field Excitation

Influence of Sampling Frequency on Magneto-Optical Imaging Under Alternating Magnetic Field Excitation

2019 ◽  
Vol 19 (23) ◽  
pp. 11591-11600
Author(s):  
Nvjie Ma ◽  
Xiangdong Gao ◽  
Congyi Wang ◽  
Yanxi Zhang ◽  
Deyong You ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Optical Imaging ◽  
Sampling Frequency ◽  
Alternating Magnetic Field ◽  
Field Excitation

Diffusion of an alternating magnetic field into a sharply cornered conductive region

1986 ◽  
Vol 405 (1828) ◽  
pp. 49-63 ◽  
Keyword(s):  
Magnetic Field ◽  
Fluid Flow ◽  
Liquid Metal ◽  
Skin Depth ◽  
Alternating Magnetic Field ◽  
Two Dimensional ◽  
Arbitrary Angle ◽  
Time Period ◽  
Field Lines ◽  
Sharp Corners

The skin-depth solution for the penetration of an alternating magnetic field into a conductor breaks down in the vicinity of sharp corners, yet it is precisely such regions which are important in the study of liquid metal flows. This paper considers the behaviour of an alternating or rotating potential field diffusing into a two-dimensional wedge of arbitrary angle. The problem is reduced to a pair of integral equations over the boundary of the wedge which are solved numerically. The variation of the field lines over a time period is shown and the implications of the locally large Lorentz force for the fluid flow are discussed.

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