| Marine diesel engines are the main power output equipment of marine systems,so improving the performance of the components has a huge driving effect in the development of the shipbuilding industry.The connecting rod and its threaded connection mechanism are key components of the diesel engine,and the strength and service life of the components during operation are also key to maintaining the overall normal operation of the diesel engine.Today as the manufacturing technology develops,enterprises have higher requirements for the quality of related components.As a result,how to improve the fatigue strength and service life of diesel engine components while ensuring their good operation has become an important research direction in the manufacturing process of diesel engine core components.Taking some diesel engine connecting rods as the research object,this thesis studies the influence of different factors on the fatigue strength of the diesel engine connecting rods and its threaded connection mechanism from the threaded connection part of the connecting rods to the entire connecting rods,by putting the processing and structural parameters of the connecting rod thread into consideration.The main research content is listed as follows:(1)SolidWorks software is used to establish a three-dimensional model for the threaded connection mechanism of diesel engine connecting rods,calculating the loading load and boundary conditions of connecting rod bolts based on the relevant theoretical knowledge of structural mechanics.It proposes to set thread pitch,bolt preload and thread connection length with different parameters,and analyzes the effect on the stress distribution of connecting rod threaded connection mechanism,After analyzing and comparing the calculation results of different parameters,we found that a reasonable design for the bolt mechanism can effectively promote the reliability of threaded connection mechanisms.(2)A model for the connection mechanism of misrun threads is established for misrun threads generated through cold extrusion experiments and the stress distribution of misrun threads under different working conditions is analyzed by using ANSYS Work Bench finite element simulation software.Then,the calculation results are compared with the results of analysis on conventional thread finite elements in Chapter two,confirming that the misrun internal threads obtained through cold extrusion methods under normal conditions will not affect the reliability of bolt connections.(3)Based on the stress analysis of the threaded connection mechanism of the connecting rods,we establish a bolt fatigue simulation model.Takin into account the influence of different parameters of the connecting rod bolt mechanism on the bolt strength,we conduct an evaluation on fatigue strength of the threaded connection mechanism and prediction for its service life.According to the fatigue analysis results,we optimize the design of the connecting rod bolt connection mechanism,and improve the fatigue strength and service life of the bolts by changing the load-bearing ratio of threads from different classes.(4)Through the research on the boundary conditions of the entire connecting rod mechanism,we analyze the static and modal characteristics of the entire connecting rods,and study the fatigue stress distribution of the entire connecting rods under different working conditions,as well as the modal shape distribution under the free model state.The research results indicate that the main invalidity positions of connecting rods are concentrated at the location where the big end cap and the connecting rod bolt are connected,the transition center of the connecting rod body,and the place of the connecting rod small end,which provides a reference for the process design of the connecting rod bolt and the overall structure of connecting rods. |
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