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Research on the Quantitative Analysis of Two-dimensional Testing of Magnetic Memory

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Tutor: RenJiLin
School: Nanchang University of Aeronautics and
Course: Measuring Technology and Instruments
Keywords: Magnetic memory testing,Two-Dimensional Testing,Stress concentration,Lissajous f
CLC: TG115.28
Type: Master's thesis
Year:  2013
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Abstract:
Magnetic metal magnetic memory testing which can detect stress concentration positions as well as the stress concentration degree on the surface of the ferromagnetic materials in the process of loading is a new non-destructive testing technology. It is different from the five major routine non-destructive testings, it detects the stress concentration positions. So it can make prevention to early damage and to catastrophic accidents. In the current state of study, the single normal characteristic parameters of magnetic memory is used to evaluate, it does¡¯t make full use of the entire information of magnetic memory testing signals, so prone to leak and misjudgment, etc.According to the above problems, work was deploied by Two-dimensional testing of metal magnetic memory based on the fracture mechanics, ferromagnetics, magnetic physics in this paper. The tangential component is led in, the method of vectorial resultant was adopted to extract tangential component signals of metal magnetic memory, and static tension condition testing is carried out for the Q235specimen, the normal and tangential magnetic signals under different stages are extracted by using two-dimensional testing system which is made in laboratory. And the two components of the magnetic signals are differential gradient. Lissajous figure analysis is led in, the lissajous figure of synthesis between normal component and tangential component and the lissajous figure of synthesis between the gradient of normal component and the the gradient of tangential component are used to analyze. It turns out that the maximum tangential component can effectively extracted by using vector synthesis principle; the area of the lissajous figure of synthesis between the gradient of normal component and tangential component can be used to determine the degree of stress concentration, and it draws that different orders of magnitude of the lissajous figure areas as thresholds are used to represent different stress concentration degrees, it is expected to provide test analysis basis for the further research on the quantitative analysis of two-dimensional detection of magnetic memory.40Cr steel specimen is as an object for high-cycle fatigue experiments in the paper, the relationship between the characteristic value of magnetic signals during the process of fatigue testing and the stress concentration position and the degree of stress concentration has been researched. The method of lissajous figure is used to draw two-dimensional curve, the relationship between area of lissajous figure and the fatigue damage state of the specimen is discussed. It turns out that the the mutation characteristics of differential gradient value can be used to accurately determine the stress concentration area caused by fatigue loading; magnetic signals appear very big change under the beginning of the loading condition, with the increase of fatigue cycles, the magnetic signal changes slowly. When the crack propagation stage in the specimen is arised, magnetic signals increase significantly; and there is a good corresponding relationship between area of lissajous figure and the fatigue damage state of the specimen.Finally, the application of metal magnetic memory two-dimensional testing method in the main poles before reduction frame machine of Z8Helicopter is researched. The magnetic memory normal component signals of the right Single ear and left two ears of the main poles before reduction frame machine of Z8Helicopter under different fatigue state were detected by metal magnetic memory diagnostic instrument. And the normal and tangential magnetic signals were detected by two-dimensional magnetic memory testing instrument. The results are used to judge the stress concentration positions and the stress concentration degree of the specimen. It turns out that the application of metal magnetic memory two-dimensional testing method in the main poles before reduction frame machine of Z8Helicopter is feasible.
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