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Study of Magnetic Memory Testing in the Mechanism and Application of the Helicopter

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Tutor: RenShangKun
School: Nanchang University of Aeronautics and
Course: Measuring Technology and Instruments
Keywords: magnetic memory testing,stress concentration,magnetic domain,orthogonal test met
CLC: TG115.28
Type: Master's thesis
Year:  2011
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Abstract:
Magnetic memory testing technique is a nondestructive testing new method forearly stage diagnosis of ferromagnetic components. In this paper, the mechanism ofmagnetic memory testing was studied by experiments based on ferromagnetism,magnetic physics, material fracture mechanical and metallography. And the feasibilityof detecting ferromagnetic components of Helicopter based on magnetic memory wasexploringly researched.Firstly, in this paper some load points were selected in the elastic stage,enhancement stage, local deformation fracture stage based on ferromagnetic materialQ235steel, magnetic memory signals were studied under different loads throughstatic tensile tests at different degrees, especially which of several points whichconsisted in the stress concentration zone and non-stress concentration. The resultsshowed that the change tendency of magnetic memory signals was similar in severalpoints. In the elastic stage, the amplitude change of magnetic memory signals wasstable. In the enhancement stage, the amplitude reached the maximum. In the localdeformation fracture stage, the amplitude showed a downward trend and eventuallystabilized.With the ferromagnetic material Q235flat sample with a central hole, thezero-crossing position and differential K, Kmax, T=Kmax/Kavgof magnetic memorysignals was studied under different loads. The results showed that the zero-crossingposition of magnetic memory signals appeared zero drift. The curve of KmaxandT=Kmax/Kavgwere similar, and which was first increased and then decreased. Thezero-crossing position of magnetic memory signals under the load point at which theKmaxand T=Kmax/Kavgappeared the maximum was the greatest stress concentrationposition, and where the specimen is easily prone to fracture. This method overcomesthe inaccuracy that only using the zero-crossing position of magnetic memory signalswas individually used to determine the stress concentration.The magnetic domain of Q235flat sample after static tensile test was observedwith the Bitter powder pattern method. Based on traditional method, the orthogonaltest method was used to prepare magnetic suspending liquid which was suitable for magnetic domain observation for Q235steel. And the changes of magnetic domain ofdifferent loaded sample were studied, especially which of several points whichconsisted in the stress concentration zone and non-stress concentration. The studyprovides an effective experimental basis to investigate the microscopic mechanism ofmagnetic memory testing and the quantification of magnetic domain.Finally, metal magnetic memory testing method is used to detect tail rotorpitch-link of Z8Helicopter. The magnetic memory signals of ring aperture and threadof tail rotor pitch-link under different fatigue state were detected by metal magneticmemory diagnostic instrument and Gaussmeter. After processing and analysis theexperimental data, the results showed that detecting tail rotor pitch-link of Z8Helicopter based on magnetic memory testing technique is feasible.
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