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crankshaft fault. It studied crack fault diagnosis though measuring the characteristics of the torsional vibration of the shafting flywheel system, and presented that model frequency and damp were sensitive parameters of cracks. The torsional vibration measuring system of the diesel had several advantages such as: easy measuring, no direct contact, cheap sensor and longevity. It was a long-term reliable alarm method for diesel shafting crack. Research group in Marine Engine Institute of Jimei University has done the research of internal-combustion engine score fault with intelligent torsional vibration diagnosis system4, and it was a successful case of on-line fault diagnosis based on torsional vibration signal.

 

3 Metal Magnetic Memory Testing Technique
In the year 1997, Russian professor A. A. Dubov brought forward correlative theory of metal magnetic memory on the World Conference on NDT, developed MMM instruments and formed MMM NDT technique5.
3.1  Theory of Metal Magnetic Memory Testing
Under the condition of the existence of the outside magnetic field, usually the magnetic field of the earth, there will appear a phenomenon in the stress concentration zone of ferromagnetic components with load that permeability of material besides the zone reduces and surface leak magnetic field increases, which is called magnetostriction. It will makes the surface magnetic field of the ferromagnetic accessory increase, and the magnetic field can remember the location of disfigurement and stress concentration zone, thus it is named metal magnetic memory.
At present, one of the most popular explanation to the magnetic memory is that, loaded by alternating stresses, unsymmetrical elasto-plastic strain will take place in the magnetic domain formed by spontaneous magnetization in ferromagnetic material, and then unequal magnetic flux density will be induced by tensile and compressive stress6. Within the magnetic field of the earth, disfigurement and stress concentration zone of ferromagnetic components will produce maximum leak magnetic field, and there will be maximum tangential component HpX of the magnetic field intensity and zero normal component HpY.
3.2  Metal Magnetic Memory Testing Instruments and Their Practical Use
Research on magnetic memory testing instruments in foreign is in pace with the technological development. Foremost of all were TSC-1M (see Fig. 1), TSCM-2FM and TSC-IM-4 stress concentration magnetic testing instrument developed by Energodiagnostika Ltd. of Russia. These instruments were associated with different types of sensor for various requirements. Software of these instruments for signal analysis and data processing was also developed in Russia. For example, MM-System data processing software produced by Energodiagnostika Ltd. was able to analyze MMM signal and display the signal in three models: 2-D, 3-D and polar coordinates model (see Fig. 2).
Internal MMM testing instruments were mainly developed by Eddysun (Xiamen) Electronic CO., LTD.  In the year 2000, EMS-2000 metal magnetic memory diagnosis instrument (see Fig. 3) with different types of sensor was produced by the company for ferromagnetic components disfigurement diagnosis. At the same time, M3DPS (see Fig. 4) software for signal analysis and data processing was developed to locate early fatigue damage7.
Applications of MMM testing in China has developed rapidly focusing on crack testing of steel we本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。