Dynamic Modeling Of Vibration And Analysis On Crack Fault In I.C.E. Crankshafts

It is well known that crankshaft is one of the most important parts of an I.C.E., the crack and even fracture failures of crankshaft are taking place frequently. In order to improve the quality of I.C.E., avoid serious accidents and limit the endangerment in min. It is highly indispensable to develop the research of diagnosis on crack fault of I.C.E. crankshaft. Obviously, this subject is very significant. A lot of studies have proved that the method based on vibration analysis is quite effective in analyzing the faults of I.C.E. So it is used here to analyze the variety of dynamic behavior of crankshaft while crack occurring and extending, investigate the fault characters that caused by crack. According to the literature we have studied and considering the condition of the experiments, this thesis is established mainly in theories. The purpose is to provide references for experiment and to lay a foundation for achieving the on-line monitoring and diagnosing on crankshaft cracks in the final.Collecting signals of vibration is the first step in the process of fault diagnosis. Here we get the vibration signals of crankshaft by numerical simulation. Due to the complicated geometric shape, boundary conditions and operation load of crankshaft, a model that available for accuracy result with the least computing scale has to be created. From the existing publications, some information is gotten that the spatial solid FEM can be the best method for solving this problem. But because of the limit of computational scale, it is just applied in the simple analysis like statics and mode. Though some methods based on the Euler beam theory have gained a certain achievement, the thickness/length ratios of every part of crankshaft exceed the applicability limit be promised apparently. In addition, the other methods being too simple or the application fields being very narrow, the results of computation are much different from experimental data. Considering the computational scale and the precision of the computational results, together with the structure and working style of crankshaft, a spatial beam element is based on Timoshenko beam theory which counts of shear deformation and inertia moment (be denominated Timoshenko beam element later) is suggested to be applied for modeling crankshaft in this thesis, and the process of building finite element model for crankshafts system included flywheel and bearing is demonstrated in detail.For showing the numerical model created is reasonable and effective, firstly the vibration modal of a one-cylinder crankshaft is analyzed with the method above and solid FEM respectively. The approximate results indicate that the two methods are valid in the same way. Subsequently, the method is applied in simulating the vibration behavior of a four-cylinder crankshaft too, and results are compared with those results and experimental data in open publications. It shows that the results obtained by the method in this thesis are more effective than the others as well as in better agreement with the observed data. During the course of above, considering flywheel is laminate and take a bigger ratio of mass in the crankshaft system, it is meshed with solid elements, and a refined model is created by a proper technique which is suggested toconnect the solid elements with beam elements. The precisions of results are improved and some errors are minished. It illustrates that the method of forming model with Timoshenko beam element is advisable. Where after, the harmonic response and the dynamic response in time domain of crankshaft in the frontal four-cylinder engine are simulated, and the results are consistent with those in modal analysis.Based on the numerical model of the crankshaft has been decided so far, it is suggested that the web containing a crack in the inner corner simulated as a rectangular cross section cracked beam element, and the crankpin include a crack at the edge of the oil-holes is modeled as a circle cross section cracked shaft element. The direction of crack in beam element is 4...