The Research On Several Key Problems In Magnetic Memory Technology Of Ferromagnetic Material

This dissertation was supported by the National Natural Science Foundation of China(51261024), Science and Technology Projects of Education Department of Jiangxi Province and Digital Signal and Image Processing Technology key laboratory of Guangdong province(2014GDDSIPL-01). As one of the most important and effective means of early detection, Magnetic memory testing has been widespread and concerned by both home and abroad nondestructive testing people. However, it still has various shortcomings in the study of problems of magnetic memory testing, such as the shortage of single criterion for defects and difficult to quantify, lack of the research of magnetic memory testing at different temperatures, inadequate of magnetic memory signal processing, etc..Therefore, consider of this case, this dissertation has done some researches. The main contents are summarized as follows:1、Describes the significance of the proposed topic, Discusses the status of researches in the principle, equipment development and other aspects of the metal magnetic memory testing technology in both home and abroad. Then pointed out some shortcomings of magnetic memory testing methods, and at last, introduced the research content and innovation of this dissertation.2 、 Elaborated the basic theory of thermodynamic coupling, force-magnetic coupling. First, introduced the basic properties of ferromagnetic material, then derived the relationship between stress and permeability through magnetic-force coupling effects of the magnetic memory testing, and describe the magneto-mechanical effect in detail. Finally, for magnetic memory detection at different temperatures, studied the constitutive equations of the elastic phase of thermal-mechanical coupling phenomenon, and describes the relationship between the magnetic, heats, and force near the Curie point. This chapter provides a theoretical basis for the whole dissertation.3、Introduces the theoretical basis of the polar coordinates analysis method of magnetic memory testing. Then use finite element simulation method of ANSYS, based on three-dimensional magnetic force coupling model to build finite element simulation model, then load and solve it to obtain the magnetic field distribution of defect’s surface, the simulation result of tangential component and normal component was then differentiating, at last analyzed the two differential signal with polar coordinates analysis method. Results of the analysis show that the polar coordinates analysis method can reflect the stress concentration level of a ferromagnetic material, and provide a reference of magnetic memory quantitative analysis.4、Design simulation program to study the effects of different materials and temperatures on magnetic memory signal by simulate some common industrial materials. First, built finite element model of the sample, and then simulate it to obtain the magnetic memory signals of the simulation model at different temperatures, then analyzed and summarized the simulation signal in order to study the influences of different temperatures on magnetic memory testing. After that, use different kinds of material, repeat the steps above to get the results of how different materials affect the magnetic memory signal. At last, comprehensively analyze the results, and find out the different materials, different temperatures effect on magnetic memory signals.5、 For the currently lack of magnetic memory signal processing, this chapter t introduce a method-empirical wavelet transform-to process the magnetic memory signal. First it introduced the principle and the characteristics of empirical wavelet transform, then verification the effectiveness of empirical wavelet transform on magnetic memory detection applications through experiments, at the same time conduct a comparative study with the traditional wavelet transform. Experimental results show that empirical wavelet transform is better than traditional wavelet transform and the empirical wavelet transform in the application of signal processing of metal magnetic memory has a good effect, and can be used as a signal processing method of magnetic memory detection.6、Summarize the efforts that have been made on several key issues in the magnetic memory testing of this dissertation and the further research of magnetic memory testing which is necessary to focus on in the future.