modelling of micropit evolution in rolling or stripdrawing of stainless steel

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1、MODELLINGOFMICRO-PITEVOLUTIONINROLLINGORSTRIP-DRAWINGOFSTAINLESSSTEELMPFSutcliffeandHRLeDepartmentofEngineering,UniversityofCambridge,TrumpingtonStreet,CambridgeCB21PZ,UKABSTRACTThemicro-plastohydrodynamiclubrication(MPHL)modelofpitevolutionbyLoandWilso

2、n(1997)isextendedtoaccountforthevariationofslidingspeedandstrainrateinrollinganddrawingprocesses.Itisassumedthatoilistrappedinisolatedpitsintheinletandisthensubsequentlydrawnoutbyrelativeslidingbetweenthetoolandworkpieceinthebite.Thevariationofpressurei

3、smodelledusingReynoldsequationandtheeffectofbulkdeformationinthestripisincludedinmodellingtheasperitydeformation.Resultsshowthatallofthefollowingfactorsareimportant:pitangle,lubricantviscosityandpressureviscositycoefficient,materialyieldstressandsliding

4、speed.Theorypredictsthatpitsarelesseasilyeliminatedatlowerspeeds,wherethelubricantismoredifficulttobedrawnoutofthepits.Pitswithlowslopesarerelativelyeasiertobecrushed,againbecausethisfacilitatestheoilbeingdrawnoutofthecontact.Themodelisverifiedbydrawing

5、experimentsoncoldrolledstripandmeasurementsonthesamplesrolledunderindustrialconditions.Agreementisgoodforthestripdrawingtests,butlessgoodfortherollingtests.Inthelatercase,itissuggestedthatthepitsmaynotbebehavingasentirelyisolatedpits,orthattheadditional

6、mechanismsatverylowspeedsmaynotbeadequatelyconsidered.KeyWords:Metalrolling;Friction;Hydrodynamiclubrication;Boundarylubrication;Surfacefinish;Pits;Stainlesssteel.TobesubmittedtoSTLETribologyTransactions,March.2000.NOMENCLATUREA(A0)Fractionofcontactarea

7、(initial)ofasperityBNon-dimensionalbulkstrainrateBaNon-dimensionalasperitystrainrateH1Non-dimensionalMPHLfilmthicknessHaNon-dimensionaleffectivehardnessofasperityNon-dimensionalgroupVickershardnessL(L0)(Initial)spacingbetweenpitsNon-dimensionalmeaninter

8、facepressure()Non-dimensionalpressureontheasperitytops(inthevalleys)QReducedpressure,RollradiusEntrainingvelocityattheentryofthebiteWNon-dimensionalasperityflatteningrateXNon-dimensionalglobalco-ordinateYYieldstressofthestripZFor