Marine Diesel Engine Piston Connecting Rod Fatigue Failure Behavior Studies

With the increasing enhancement of marine diesel engine,high temperature and pressure put forward more stringent requirements for strength and fatigue reliability of piston connecting rod mechanism of diesel engine.Fatigue failure of piston connecting rod has always been an important factor affecting the service life of marine diesel engines.The research on fatigue failure behavior of piston connecting rod mechanism of marine diesel engine and the accurate prediction of fatigue danger point and fatigue life of piston connecting rod mechanism are not only of great significance to improve the working stability,economy and safety of marine diesel engine,but also provide basis for the design,development and maintenance time of piston connecting rod of marine diesel engine.Firstly,the piston of a marine diesel engine is taken as the research object,the temperature field and thermal-mechanical coupling analysis are carried out to predict the thermal-mechanical coupling fatigue life of the piston under full load and stable conditions based on the results of thermal-mechanical coupling analysis.To explore the effects of changing the thickness of heat insulation layer on piston head,the radius of throat fillet and the depth of inner groove on temperature field,thermo-mechanical coupling stress and deformation as well as thermalmechanical coupling fatigue life under full load and stable condition of piston.The results show that the minimum fatigue life of the piston under full load and stable condition is located at the piston pin hole.Adding a certain thickness of titanium alloy heat insulation to the piston head can reduce the maximum thermal-mechanical coupling stress of the piston,reduce the working temperature of the piston ring area and increase the thermal-mechanical coupling fatigue life of the piston under full load and stable conditions.Secondly,high temperature low cycle fatigue test of piston material was carried out to study the low cycle fatigue behavior of piston under start-stop conditions.The Manson-Coffin low cycle fatigue life prediction model of piston material and a new model based on power index function were established.The comparison between the two models shows that the new model based on power index function has smaller error band and standard deviation and more accurate prediction results than the Manson-Coffin model in life prediction.Then,a new model is used to predict the low cycle fatigue life of pistons under starting and stopping conditions.It is found that the minimum fatigue life of the piston under start-stop condition is located at the top surface of the piston,which is mainly due to the large strain amplitude on the top surface of the piston during the start-stop process.Finally,the fatigue behavior of connecting rod of marine diesel engine is analyzed.The stress and deformation distribution of connecting rod under maximum tensile and compressive conditions are analyzed.The fatigue life of connecting rod is predicted based on the simulation results of maximum compression condition.The results show that the minimum fatigue life and safety factor of connecting rod are both located at the connection between the body and connecting rod small end,and the minimum safety factor is larger than the minimum safety factor required by connecting rod design.