表面质量对疲劳强度的影响(英语).ppt

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1、ChenJunwei,Group3May12,2011InfluenceofSurfaceQualityonFatigueStrengthThefatiguelifeofamachinedpartdependsstronglyonitssurfacecondition.Andtheeffectofresidualstressonfatiguelifeismorepronouncedthanthatofsurfaceroughness.Somedefectsofsurfacequalityhaveaconsiderableeffectonfatiguestrength,suchas

2、strainhardeningandresidualcompressivestresses.Stressconcentrationoccurseasilyatthetroughsofsurfaceroughness,especiallythegrooveandfilletcorner,whichcanleadtofatiguecrackandacceleratethefatiguefailure.AbriefintroductionMaterialandexperimentalset-upThetestspecimensweremachinedbyturninginwetcond

3、ition.Residualstressesweremeasuredbymeansoftheblindholedrillingmethod.SurfaceroughnessThesurfaceroughnessofthemachinedpartislargelydeterminedbythefeedandtoolnoseradius.Alargefeedwillgiveshortercuttingtimesbutapoorsurfacequality.Alargenoseradiuswillgenerateabettersurfacequality.Butanexcessivel

4、ylargenoseradiuscanleadtovibrationtendencies,unsatisfactorychipbreakingandshortertool-life.Atheoreticalmodelforsurfaceroughnessisapproximatedbythefollowingequation:wherefisfeedrate(mm/r)andrεisthetoolnoseradius(mm).TheFigureillustratestheeffectofthenoseradiusonthesurfaceroughnessforthecutting

5、conditionemployedforthefatiguetest(f=0.2,r=0.2,0.4,0.8).TheresultspresentthatthevalueofRmaxparameterincreaseswiththedecreasingofnoseradius.ResidualstressAftertheturningoperation,theresidualstressesweremeasuredusingtheblindholedrillingmethod.Themachiningofroundsampleswascarriedoutwithdifferent

6、feedratesandnoseradius.Thesedataaremeasuredbytheblindholedrillingmethod.Itshowsresidualstressincreaseswiththedepth.Wecanseethatanincreaseoffeedratecausesanincreaseofcompressivestressesinbothdirections.Ontheotherhand,anincreaseofthenoseradiusoftheinsertcausesadecreaseofthecompressiveresidualst

7、resses.Intherotatingbendingfatiguetests,residualrotationspeedwas3800rev/min.Whenthenumberofrotationexceeded107,thetestwasstopped,withthetestspecimennotbreakunderthatcondition.Althoughthesurfaceroughnessofspecimenswithre=0.2ishigherthanthatwit