| The crankshaft is the core moving part of diesel engine due to the severe working condition and the loaded complex impact alternating load,the strength and fatigue life of crankshaft directly affect the reliability and life of the diesel engine,which means the crankshaft design is one of the key and difficult points of engine design.The crankshaft may resonate within the working speed range of the engine when it loaded the periodic and complex dynamic loads,the resulting sharp increase of dynamic stress induces fatigue failure of the crankshaft.In this paper,the fatigue life of crankshaft was studied based on the traditional fatigue life analysis and the crankshaft dynamic characteristics,the results can be used in the reliability design of crank-connecting rod mechanism.The crankshaft of a typical multi-cylinder high-speed diesel engine was selected as the research object in this paper,the multi-body dynamics simulation of the crank-connecting rod was carried out to obtain the load spectra of the crank pin of the crankshaft,the simulations was based on the working principle of the crank-connecting rod mechanism.The stress-strain of the crankshaft was analyzed with FEM(finite element method)under engine design condition,the maximal equivalent stress and the corresponding firing position and time were obtained.A quasi-static analysis was carried out for the loading position of the maximal equivalent stress on the crankshaft.The fatigue life analysis of the crankshaft was conducted using nominal stress method,the simulation combines the stress results of the quasi-static analysis,the fatigue characteristic curve of the crankshaft material and the load spectrum of the crank pin at the loading position of the maximal equivalent stress.The effects of structural parameters on the maximal equivalent stress and the fatigue life were studied,the parameters includes the spacing of parallel connecting rods and the fillet angle.The vibration characteristics and the dynamic response of the crankshaft were analyzed.The vibration fatigue life of the crankshaft loaded different single-frequency excitation were calculated based on the crankshaft vibration characteristics,the variation of the stress and the fatigue life of the crankshaft loaded the dynamic load were studied.The fatigue life of the crankshaft loaded the dynamic load was predicted using the Dirlik method,which was based on the crankshaft stress under the design condition,The results show that the calculation result of life considering the vibration characteristics of the crankshaft is lower than that of the nominal stress method,indicating that in the evaluation of crankshaft fatigue life,it is necessary to take into account the vibration factors for prediction according to the actual working conditions of the crankshaft,and the research results can provide a reference for the reliability design of the crankshaft. |
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