Fatigue Damage Analysis And Accelerated Life Test Design For Piston Parts Of A Marine Diesel Engine

As a key component of marine diesel engines,the piston is subject to complex forces during engine operation,and at the same time withstands the effects of high temperature environments.During long-term work,it often leads to cracks in the piston pin seat,piston burn-out,and sticking of the cylinder.The fatigue reliability of the piston is directly related to the working reliability of the diesel engine.Therefore,it is necessary to perform fatigue damage analysis and fatigue test on the piston.Based on a comprehensive analysis of domestic and foreign piston thermo-mechanical coupling analysis methods,related fatigue tests and theories,the piston thermo-mechanical coupling analysis technology is used as the entry point to establish a theoretical model for piston heat transfer analysis and a theoretical model for stress field analysis.The thermoelastic finite element analysis model uses the pre-processing software to mesh the parts of the piston to provide a theoretical model basis for subsequent simulation analysis.The reliability of simulation cannot be separated from the support of key data.Firstly,the in-cylinder combustion model was established using GT-Power,and the change of the combustion chamber temperature and pressure in the cylinder of the diesel engine with the angle of rotation was obtained to determine the maximum combustion pressure and average temperature in the cylinder.Secondly,the empirical formula is used to calculate the heat transfer coefficients of the piston top surface,side surface,oscillating cooling cavity and piston skirt,and the temperature distribution of the piston is obtained through ABAQUS simulation.Then analyze the movement characteristics of the piston,get the inertia force and the bolt pretightening force that the piston runs under standard conditions,and simulate the piston stress field distribution result.Finally,according to the results of temperature field and stress field,the coupling results of the thermo-mechanical coupling of the piston were obtained by setting the load analysis step for sequential coupling.For the analysis of piston fatigue performance,FEMFAT software is used to obtain the safety coefficient distribution of the piston head and piston skirt,and the key force areas of the piston head and piston skirt;the S-N curve and average stress of the material are corrected,and the piston in each Fatigue life under working conditions with Miner Criterion.By using the Aeron theory to consider the interaction between loads,the damage evolution curves of the piston before fatigue failure under different operating conditions are obtained,and compared with the Miner criterion for analysis.Using the calculation results of simulation combine with the theoretical model of acceleration test,and Matlab to obtain the accelerated life curve of the piston under mechanical load,thermal load and thermo-mechanical coupling conditions,and the function relationship between load and life is obtained.Based on the inverse power law model in the acceleration model,make an accelerated life test scheme for piston mechanical stress.By constructing a piston mechanical fatigue test bench,making a matching piston mechanical fatigue test fixture,hydraulic system,control system,and software platform to generate a sinusoidal pressure with a phase difference of 180 ° between high pressure and low pressure in the pressure chamber above and below the fixture.The mechanical load on the cylinder is compared with the crack condition of the test piston and the crack condition predicted by simulation through a fatigue test to verify whether the mechanical fatigue test bench can meet the design requirements..