The Research Of Mechanism About Magnetic Memory Testing

When a ferromagnetism items is under the application of stress, the phenomenon that the tangential component of magnetic leakage field has maximum value and that the normal component of magnetic leakage field changes polarity and acquires zero value at the stress concentration zone will take place. According to this phenomenon, the metal magnetic memory testing (MMMT) can diagnose accurately the stress concentration position of metal items with applied stress, and make the early diagnosis realization. To explain the phenomenon theoretically, below is the compendium of the dissertation:1. Summarized the fundamental theory of ferromagnetics, metal mechanics and electromagnetics which is connect to the metal magnetic memory testing. The metal magnetic memory testing is a new technology which is special diagnose ferromagnetism materials with applied stress in earlier, and is belong to electromagnetic non-destructive testing (NDT). So the fundamental theory of ferromagnetics and the mechanics property and the electromagnetism property of metal is the theoretical foundation, some knowledge connected to them are summarized in this dissertation.2.The derivation of the effective magnetic field expression for the ferromagnetism materials with applied stress. A ferromagnetism rod is chosen as sample which is often used in the experiment of materials mechanics, was placed in the earth magnetic field and was under the application of stress. According to the mean field theory which is based on the phenomenological theory of ferromagnetism, using the conception of effective magnetic field, an effective magnetic field expression for ferromagnetism rod affected by stress in the geomagnetic field is derived.3.The derivation of the expression for the mean field parameter. The total energy expression of the sample is build through analyzing its energy composition. According to the principle of the minimum energy, using theconnection between stress and strain and the connection between magnetostriction and magnetism strain, an expression for the mean field parameter is derived.4. The theoretical explanation for the mechanism of magnetic memory testing. According to the effective field expression which has been derived in former, the phenomenon that the tangential component of magnetic leakage field has maximum value and the normal component of magnetic leakage field acquires zero value at the stress concentration zone of positive magnetostriction ferromagnetism materials under the application of tensile stress and negative magnetostriction ferromagnetism materials under the application of compressive stress is explained theoretically through analyzing and discussing.5. Simulation computation. For the purpose of showing the analysis result vividly, a simulation computation in the software of Matlab is accomplished and the distribution curves of the magnetic field are drew.