Research Of Magnetic Memory On-line Detect On The Crack Of Marine Diesel Engine Crankshaft

The crankshaft is one of the primary components of the diesel engine, which is high-cost and works in bad condition. Once damaged, it would not only bring the fatal destroy to the marine diesel engine, but also imperil the safety of ships directly. Presently, the stress of the crankshaft has been accounted when designing, or checked-up after the accident. However, as a result of the error of setting, the unequal combustion of each cylinder, the parts worn off, aged parts, the vibration of the shafting, etc, the factual stress of the shafting can not maintain the theoretic state, the rupture shafting of the engine or the tail-shaft occurred frequently. Diagnosing the crack of shafting on-line will avoid the engine to be destroyed and reduced the loss of accident greatly. As a new kind of metal nondestructive testing technique, the Metal Magnetic Memory Testing (MMMT) technique was brought out in the last ten years, which apply to the crankshaft as the ferromagnet, to find the stress collected and detect the crack. The sensor used as MMMT is simple, and will not affect the function of diesel engine. It adapt to long-term detect online.The primary task of this paper is:1. The mechanism of the MMMT technique is studied. Considering the demand of the MMMT, the formula of piezomagnetism action is educed, through deducing magnetoelastic effect. The Magnetism Memory phenomenon is verified by carrying out experiments, and bring out one important characteristic of the Magnetism Memory, namely HpY(0) position. The position is superposition with prefabricated crack's position, stress concentration's position can be located through scanning along different generatrixex of piece test.2. The information of the crankshaft's crack of diesel engine is collected to analyze and research the growing rule of the crack early. The information is collected and classified from the shipyard and the marine engineering department and the literature, filtrate the representative crack of shafting. Using the fracture mechanics and crankshaft crack propagation rule which consulted the stress-intensity factor to analyzing the fracture process of the crankshaft.3. Constructing the simulative experimental platform, validating the fracture process of crankshaft. The small diesel engine is used for building the experimental platform mainly, which can carry out different test in case of the variable velocity, variable load, the variable temperature and the oil mist in the engine crankcase. It helped the magnetic memory test to come true, with practicability and reliability.4. Studying the characteristic of magnetic memory signal of the diesel engine crankshaft, which be in the variable velocity, variable load and variable temperature, to improve the function of the software and hardware of the diagnostic system, and it will create the condition for the science and research in the future.