| In recent years,with the continuous improvement of thermal efficiency of diesel engine,the internal combustion engine is changing towards higher pressure and greater compression ratio.Combustion chamber components,including cylinder liner,piston and other engine parts,need to bear more and more severe thermal and mechanical loads.The intense load puts forward higher requirements for the strength of cylinder liner and other parts.For the cylinder liner with new coating,the research at home and abroad are focused on improving the surface hardness of the coating to reduce the friction coefficient,or improving the engine emissions,etc.,but there is still a lack of targeted system scheme in the pressure impact fatigue performance analysis of the cylinder liner.According to the in cylinder pressure curve of a diesel engine with explosion pressure of 22 Mpa,a systematic fatigue test scheme including test procedures and experimental equipment was established for a cylinder liner with base material of40 Cr medium carbon steel and 2 mm thickness Zr O2 ceramic coating as strengthening heat insulation structure,The stress-strain analysis and numerical calculation of fatigue life prediction based on finite element simulation are carried out,and the numerical analysis results are compared with the experimental results.(1)Referring to the research work of domestic and foreign researchers on the fatigue strength test of engine parts in recent years,the test process and operation method of experimental equipment based on hydraulic pressure impact fatigue test are formulated.According to the pressure loading curve required by fatigue test,a hydraulic system simulating the gas shock wave curve is constructed based on the control logic.In view of the fitting transformation of the clamping cylinder liner cavity and the hydraulic oil circuit,a strong sealing scheme with O-ring matching lattice was designed.In terms of structure,the assembly scheme of the high pressure resistant cavity and the secondary processing requirements of the cylinder liner related components were formulated;In the aspect of sealing,according to the design standard of pressure vessel,the minimum wall thickness of pressure shell is obtained;The specification parameters of bolts and screws for fastening cylinder head and lower body are selected;According to the two key positions between lower body and cylinder head,piston and cylinder sleeve,a detailed sealing scheme is established.Finally,the hydraulic impact fatigue test system is constructed,which consists of three modules: power area,control area and high pressure resistant body area.(2)The finite element model of high pressure resistant assembly is established,and the stress-strain calculation and fatigue life prediction of cylinder liner under pressure impact load are analyzed by using ANSYS engineering software.The maximum stress of cylinder liner inner wall is about 198.8mpa during the test,and the main dangerous areas and failure order of fatigue failure are obtained through the stress-strain nephogram;Based on Goodman correction method,the pressure impact fatigue model of ceramic coated cylinder liner is established according to the nominal stress Sn curve.It is estimated that the life of cylinder liner matrix is infinite,and the life of ceramic coating is 1.02 million pressure impact cycles.(3)Finally,the hydraulic impact fatigue test of cylinder liner is carried out in the step of 20000 times,and it is found that the actual life at the maximum stress of inner wall is about 800000 times.In view of the deviation between the calculation results and the numerical calculation results,many factors affecting the accuracy of pressure impact life prediction are discussed,and the calculation defects in the prediction process are analyzed.From test to simulation,and then to analysis,comparison and review,a more meaningful fatigue life analysis and testing work has been carried out. |
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