The Basic Research On Fretting Fatigue Of Engine Block Based On Simulation

Fretting is a kind of little amplitude relative movement which is occurred between thesurfaces of mechanical components，it has great influence on fatigue life. With thedevelopment of high power density（HPD）engine，fretting fatigue failures frequently occurredon the block face contacted with the bearing cap when engine work.Based on the theories ofthe fretting contact dynamic，and the finite element simulation of contact problems，the basisresearch of fretting fatigue on the engine block-main bearing cap and its simulationcomponent，which is rectangular pad-specimen were carried out in this paper. The rectangularpad-specimen，whose contact is similar to engine block-main bearing cap，was as the researchobject，the influence of cylic load，vertical pressure and friction coefficient on the distributionof fretting contact stress，the state of contact surface，the position of fretting fatigue crackinitiation were researched；the fatigue parameters approach on critical plane was put forwardfor the first time when the influence of above three parameters on the probability of thefretting fatigue occurred on the specimen surface was studied. To the engine block-mainbearing gap system as the object，based on the introducing advanced fatigue parametersapproach on critical plane，the position of fretting fatigue crack initiation on the block facecontacted with the bearing cap were predicted，the effectiveness of breakout pressure andpreloaded force on the probability of the fretting fatigue was investigated，explore wasdevoted to the research of the fretting fatigue on the block face contacted with the bearingcap.On the analysis of the fretting fatigue on the rectangular pad-specimen，the geometry andfinite model were established，the static force under different parameters was calculated. Based on the calculated results，two methods for judging contact state were introduced，theone is take advantage of the mormal relative displacement，the other is take advantage of therelationship between maximum static friction and actual friction；the influence of cylic load，vertical pressure and friction coefficient on the distribution of fretting contact stress，the stateof contact surface，the position of fretting fatigue crack initiation were researched；thedistribution of fatigue parameters SWT(Smith-Watson-Topper) and FS(Fatemi-Socie) oncritical plane along the contact path were analysised，the position of fretting fatigue crackinitiation on the specimen surface were predicted，the analysis results using SWT and FSparameter were compared，the SWT parameter showed a good correlation with the frettingfatigue crack position for specimen fretting phenomenon；using the SWT parameter, theeffectiveness of the above three parameters on the probability of the fretting fatigue wasinvestigated.On the analysis of the fretting fatigue on the the engine block-main bearing cap，thegeometry and finite model of the engine block-main bearing cap structure were established，the stress filed and displacement field of the model were analysised under pretension andburst condition；the SWT and FS parameters were analysised to predict fretting fatigue crackposition on the block face contacted with the bearing cap，As the results，the SWT parametershowed a good correlation with the fretting fatigue crack position for engine blockphenomenon.finally，using the SWT parameter, the effectiveness of breakout pressure andpreloaded force on the probability of the fretting fatigue was investigated.