The Search Of The Magnetism Memory Technology And Its Application Method

In modern industry, about 80% or more structural breaks are caused by the fatigue invalidation. With traditional method of nondestructive test, through testing related parts of material, equipments and components, all shaped macroscopical defects and most of tiny blemish can be availably discovered. But to early damnification of metal components in service, it is difficult to diagnose and evaluate with this method. As a nondestructive testing technique for diagnosing metals and components in service in early .stage, the Magnetism Memory Technology is widespreadly attached importance as soon as being published and develops at a very high speed. But, as the developing time of the Magnetism Memory Technology is very short, some theories are not very mature. For example, the Magnetism Memory Technology can only find out problems (all are called stress concentration. It is still not advanced enough to make sure the mechanism of the pressing magnetization of detectived parts and the actual condition of blemish, even to measure degree of stress concentration. Other examination methods must be used to countercheck. These are all the obstacles to restrict the practical use and development of the technology.Aiming at the problems of the Magnetism Memory Technology, this paper study the theories of Magnetic Memory, the analysis of the Magnetic Memory signal, the influence factors of the Magnetic Memory Testing effect. A large number of blades of Steam Turbines are practical tested with existing theories, instruments and accessorial signal analysis software of the Magnetic Memory.Main works in this text include:1. The mechanism of the Magnetism Memory Technology is studied. Through deducing magnetic elastic effect, the problem of the direction of piezomagnetism is resolved. Combining the detailed thermodynamics deduction, the formula of piezomagnetism action is educed. The Magnetism Memory phenomenon is verified through carrying out experiments, and bring upon an important characteristic of the Magnetism Memory, namely Hp1 (0) position is superposition with prefabricated crack' s position, stress concentration' s position can be located through scanning along different generatrixes of piece tested.2. The magnetism of detectived object is analyzed and studied. The Magnetism Memory Testing effect has relation to the magnetism of matrials tested. To the noferromagnet, the testing signal amplitude would consumedly minish, even can't be examined. Setting out from the microscopic construction of materials and depending on the research for the exchange theory and the energy zone theory, this dissertation analyzes recount integral factor (A) , and finds out the source of the antimagnetism, the paramagnetism and the ferromagnetism, and points out the insufficiency of the exchange theory, and studies the alloy' s magnetism3. The relation of the Magnetism Memory signal and crack width is studied; Through the examination experiment on three tube pieces' crack part, the relation of crack width, the maximum of leak magnetic field and differential coefficient is found out. Namely along the crack, when the crack width increases, the K raises too. When crack width changes from wide to narrow, the K does not immediately minish, but continuously enlarges first, reduces then, and does not return in original route.4. The influence factor of the Magnetism Memory Technology is studied, mainly including detective environment, the placing direction of piece tested, lift, the scanning speed, etc. The influence of examination environment is studied on experiment and theories, and the conclusion is educed that when the piece tested is dismantled from its original environment, the leaking magnetic field strength will minish, and the zero point of leaking magnetic field also will move towards the top. Through the experiment, the result that the Magnetism Memory Technology suffer little effect of lifting and scanning speed is conclude. But the different ordering direction of component and sensors will result in the move of zero poin...