The Study On The Prediction Method Of Mechanical Fatigue Life For The Heavy Duty Diesel Engine Piston

The piston is one of the most important parts of the internal combustion engine. In theprocess of operation，it is loaded periodcally by the mechanical load of the gas pressure、reciprocating inertia force and thrust side，often leading to a crack of the piston pin，Initialwear of thering slot and so on，and are directly related to the work reliability and the use of ofthe durability of the theinternal combustion engine. Therefore，the fatigue life prediction isvery necessary for the piston.It is important that the engine piston strength and fatigue analysis，and the basic theory offatigue is introduced，including the conception and classification of the fatigue，and the theroyof cumulative damage，the s-n curve，the model of fatigue life prediction and influencingfactor of fatigue .The piston is loaded by the mechanical strength and is analyzed by thetransient finite element，and then，is estimated to the fatigue life according to the transientstress analysis results，the surface roughness and the rectification of Goodman and gerber isdiscussed.First of all，the three dimension model of the piston group is established by the PRO/E，including establishment of the model of the the piston，the piston pins and the connecting rod，the choice of the material，and the grid is divided by the ANSA.then, the piston is loaded bythe mechanical strength and is analyzed by the transient finite element:firstly，the contactconstraints of the model is established，that is, the piston pin a-pin hole bushings、the pistonpin- the piston pin a、the piston pin-connecting rod bushing and connecting rodbushing-connecting rod is contacted；secondlly，the boundary conditions of the model isestablished，that is，the upper of the piston pin a is constrainted fully，the bottom of theconnecting rod is constrainted fully，and the quarter of the plane of symmetry is constrainted symmtrically；thirdlly,the load is established，that is，the gas pressure is loaded to the topsurface of the piston，the reciprocating inertia force is loaded to the piston；fourthly，the loadstep is setted up，the type of the the load step is the slope load，and the model is analyzed byimplicit algorithm of the full method，and the maximum stress is defined in the the upper ofthe piston pin a. Finally，the fatigue life of the model is predicted by the ANSYS/FE-SAFE，the ANSYS stress results of the previous chapter is imported to the FE-SAFE,the loadspectrum is prepared，fatigue parameters of the material is defined by the the material seegerapproximate algorithm，the method of the maximum principal stress is determined，and thefatigue life of the is estimated by the previous data. Lastly，the affect of the surface roughnessthat is researched to the the fatigue life is provided for the reliability of the piston.