TribologyInternational73(7
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TribologyInternational
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Competingfailuremechanismandlifepredictionofplasmasprayedcompositeceramiccoatinginrolling–slidingcontactcondition
Jia-jieKanga,Bin-shiXub,Hai-douWanga,b,n,Cheng-biaoWanga
SchoolofEngineeringandTechnology,ChinaUniversityofGeosciences,Beijing100083,China
NationalKeyLabforRemanufacturing,AcademyofArmoredForcesEngineering,Beijing100072,China
articleinfo
Articlehistory:
Received11November2013Receivedinrevisedform11January2014
Accepted17January2014
Availableonline28January2014Keywords:
PlasmaspraycoatingsRolling–sliding
Competingfailuremechanism
ThecompetingfailuremechanismandlifepredictionofplasmasprayedAl2O3-40wt%.TiO2compositeceramiccoatingsunderrolling-slidingcontactconditionswereinvestigatedonadouble-rolltestmachine.Themaximumshearstressdistributioninthecoatingswasanalyzedbythefiniteelementmethod.Weibullfunctionwasusedtocharacterizethelifedistributionofthecoatingsunderdifferentrolling–slidingcontactconditions.Thefailuremodesweremainlysurfaceabrasionandadhesivedelaminationduringthisinvestigation.Themechanismofthecompetingbetweensurfaceabrasionandadhesivedelaminationwasdiscussedindetail.
&2014ElsevierLtd.Allrightsreserved.
1.Introduction
ThermalsprayedAl2O3-40wt%.TiO2compositeceramiccoat-ings(AT40coatings)havewidelybeenusedtoimprovethesurfacepropertiesofmechanicalcomponentsfortheirexcellenthigh-temperatureresistance,corrosionresistanceandwearresistance[1,2].Supersonicplasmasprayingisasuitablemethodforprepar-ingAT40compositeceramiccoatingsduetothehighflametemperatureandfastparticlevelocity[3–6].
Wearandrollingcontactfatigue(RCF)arethemostcommonfailuremodesofAT40coatingsunderrolling–slidingcontactcondition[7,8].Wearfailurewhichisintheformofsurfacematerialremovaloftenoccursunderslidingcontactcondition.RCFfailureisapersistentdamageprocesswhichinvolvescrackingorpitting/delaminationlimitedtothesubsurfaceofmaterialsunderrollingcontactcondition.Therefore,itcanbeconsideredthatwearandRCFsimultaneouslyoccurandinfluenceeachotherunderrolling-slidingcontactcondition.TheRCFbehaviorsofthermalsprayedcoatingshavewidelybeeninvestigated[9,10].Theinfluenceofmainparameters(i.e.contactstress,surfaceroughness,coatingthickness,bondingstrength,rollingvelocity,andcoatinghardness,etc.)ontheRCFfailuremechanismandRCFliveswerediscussed[11–14].However,mechanicalcomponentsarenotusuallyunderpurerollingcontactbutrolling–sliding
contact[15,16].Onlyafewresearchesonthethermalsprayedcoatingsunderrolling–slidingcontactconditionweredonetoanalyzetheRCFfailureprocess[17],buttheslipratiosinthoseresearcheswerelimitedtonolargerthan50%.Therefore,themechanismofcompetingbetweenwearandRCFofthermalsprayedcoatingsunderrolling-slidingcontactconditionswithlargerange(0$75%)shouldbeinvestigatedindetail.
Inthepresentresearch,thecompetingfailuremechanismandlifeevolutionlawofplasmasprayedAT40compositeceramiccoatingsunderrolling–slidingcontactconditionswiththeslipratiosofR1 1/4 0%,R2 1/4 25%,R3 1/4 50%,andR4 1/4 75%wereindetailstudiedonadouble-rolltestmachine.2.Experimentaltestprocedure2.1.Coatingdeposition
TheAT40coatingsandNi/AlbondingcoatingsweredepositedonthetemperedAISI1045steelrollersusingsupersonicplasmaspraytechnology.TheplasmasprayparametersarelistedinTable1.Thesubstratesurfacewassandblastedandthenpreheatedtoabout2001Cbeforespraying.
Thecoatingqualityisgreatlyaffectedbytemperatureandvelocityofmeltedparticles,whichweremonitoredbySprayWatch-2imonitor.ThetemperatureofmeltedparticleswasashighasaboutC.Duetothemechanicalcompres-sioneffectofthenozzle,thevelocityofparticlesatthedistanceof100mmfromthenozzlewasabout460$500m/s[9],whichismuchhigherthanthatusingairplasmaspraytechnology(about
Correspondingauthorat:SchoolofEngineeringandTechnology,ChinaUniversityofGeosciences,Beijing100083,China.Tel.:?;fax:?.
E-mailaddress:(H.-d.Wang).X/$-seefrontmatter&2014ElsevierLtd.Allrightsreserved.
http://dx.doi.org/10.1016/j.triboint.
J.-j.Kangetal./TribologyInternational73(7129
Plasmasprayparameters.
Al2O3-40wt%TiO2compositeceramiccoatingArgongasflow(m3/h)2.8Hydrogengasflow(m3/h)0.4Nitrogengasflow(m3/h)0.6Sprayingcurrent(A)440Sprayingvoltage(V)110Sprayingdistance(mm)100Powderfeedrate(g/min)30
Ni/AlbondingcoatingArgongasflow(m3/h)3.4Hydrogengasflow(m3/h)0.3Nitrogengasflow(m3/h)0.6Sprayingcurrent(A)320Sprayingvoltage(V)140Sprayingdistance(mm)150Powderfeedrate(g/min)
200$300m/s).Highvelocityofthemeltedparticlescanincreasetheimpactenergyoftheparticlesandimprovethebondingstrengthbetweenthecoatingandsubstrate.ItisgenerallyacceptedthatthequalityofAT40compositeceramiccoatingbenefitsfromthehightemperatureandvelocityofthemeltedparticles.
ThesurfaceandcrosssectionmorphologiesofplasmasprayedAT40coatingareshowninFig.1.Thecoatingsurfacewasrelativelysmooth,andalmostnounmeltedparticleormicrocrackwasobserved,asshowninFig.1(a).Fig.1(b)showsthedensemicro-structureofthecrosssectionofAT40coating.Onlyafewmicro-poresexistedinthecoating.TheNi/Albondingcoatingwithathicknessof80μmcanreducetheelasticmismatchbetweenthesubstrateandcompositeceramiccoatingtoimprovethebondingstrengthsignificantly.ThethicknessofAT40coatingwasabout400μm.Thebondingstrengthmeasuredbythedualtensiletestmethodwasashighas35MPa.Theporositymeasuredbytheimageanalysismethod(IAM)[18]wasabout1.12%.2.2.Experimentalconditionsandprocedures
AnovelRCF/wearmultifunctionaltestmachinewasusedtoinvestigatetheRCF/wearcompetingfailuremechanismofplasmasprayedAT40coatingunderdifferentrolling–slidingcontactcon-ditions.ThetestmachinewasindetaildescribedinRef.[19].Theprominentcharacteristicofthetestmachineisthattheslipratiobetweentherollersisabletochangefrom0%to100%,sincetherollerswereindividuallydrivenbyamotor.Thetestswereperformedunderfourdifferentslipratiosof0%,25%,50%,and75%.ThevelocitiesofthetestrollersandstandardrollersareshowninTable2.
Fig.2showstheschematicofthetestrollerandstandardroller.Theloadwasappliedtothetestroller.ThefailureprocessoftheAT40coatingsprayedonthetestrollerwasmonitoredbyanacousticemission(AE)probeforitssensitivitytoplasticdeforma-tionandbrittlefractureofmaterials.ThethresholdvalueofAEsignalswassetas60dB,andthefailurepointwasdefinedwhentheAEcountwashigherthan350.Oncethefailurepointwasjudged,thetestmachinewouldstopautomaticallyandthefailuremorphologieswereimmediatelysavedforanalyzing.
ThematerialofstandardrollerwastemperedAISI52100steel.ThesurfaceroughnessvaluesforthetestrollerandstandardrollermeasuredbyusingOlympusOLS4000laser3Dmicroscopewere0.6270.01μmand0.3670.01μm,respectively.Themicro-hardnessvaluesofthetestrollerandstandardrollermeasuredbyaVickers-hardnesstesterwiththeloadof100gwere910HV0.1and770HV0.1,respectively.
Fig.1.SurfaceandcrosssectionmorphologiesoftheAT40coating.(a)Surfacemorphology(b)Crosssectionmorphology.
Thevelocitiesofthetestrollersandstandardrollers.Slipratio
R1 1/4 0%R2 1/4 25%R3 1/4 50%R4 1/4 75%Standardroller(m/s)0.80.628Testroller(m/s)
ThecompetinglifetestsforAT40coatingswereperformedunderafixedcontactstressof0.75GPa.ThecorrespondingloadwascalculatedbytheHertzequation(Eq.(1)).sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffis 1/4 F?∑ρ?
wheresmaxisthemaximumcontactstress,andthevalueis0.75GPa;FListhelengthofthecontactline,and
130J.-j.Kangetal./TribologyInternational73(7
Fig.2.Schematicofthetestrollerandstandardroller.
thevalueis5υ1andυ2arePoissonsratiosofthetestroller(AT40coating)andstandardroller(AISI52100steel),respectively,andbothofthevaluesare0.3;E1andE2aretheelasticmodulusofthetestrollerandstandardroller,respectively,andthevaluesofE1andE2are173GPaand219GPa,Σρisthesumofprincipalcurvaturesofthetestrollerandstandardroller,andthevalueis1/15mm?1.
3.Resultsanddiscussion
3.1.Failuremodesandcompetinglives
ThefailuremodesandcompetinglivesofAT40coatingunderdifferentslipratiosareshowninTable3.Thefailuremodesunderthepurerollingcontactcondition(slipratioR1 1/4 0%)weremainlydelamination,spalling,andsurfaceabrasion.However,spallingfailurehardlyoccurredunderrolling–slidingcontactcondition(slipratioR2 1/4 25%,R3 1/4 50%,andR4 1/4 75%).Inaddition,theprob-abilityofdelaminationfailureincreasedwiththeslipratioincreasing.
3.2.Lifepredictionplots
WeibullfunctionproposedbyW.Weibull[20]haswidelybeenusedtocharacterizetheprobabilitydistribution.ManyresearchesindicatethatWeibullfunctioncanwellcharacterizetheRCFlifeofmechanicalparts[21].
Two-parameterWeibullfunction(Eq.(2))wasusedtoanalyzethecompetinglifedataofAT40coatings.P?N? 1/4 1?e??N=Na?
whereP(N)istNNathecharacteristiclifeunderthefailureprobabilityof63.2%;βtheslopeofWeibullcurve.βdefinedastheshapeparameterofWeibullfunctioncanreflectthedispersionofthefunction.Thehighertheβ,thesmallerthedispersionofthefunction.
Thetwoparameters(Naandβ)ofWeibullfunctionwereevaluatedusingthemaximumlikelihoodestimation(MLE)method[22],asshowninEqs.(3)and(4).∑ni 1/4 1Niβ
∑ni 1/4 1N?
i 1/4 1?3 !1=β
?4ThevaluesofNaandβcalculatedbyEqs.(2)and(3)areshowninTable4.
ThevaluesshowninTable4weresubstitutedforNaandβinEq.(2)toobtaintheWeibullcurvesofcompetinglivesofAT40coatingspecimens,asshowninFig.3.Thehorizontalcoordinateandlongitudinalcoordinateofthecurvesarenumberofcyclesandpredictedfailureprobability,respectively.Therefore,theWeibullcurvescanbeusedasP–NcurvestocharacterizetheevolutionlawofcompetinglivesofAT40coatingunderdifferentslipratios.ItcanbeseenfromFig.3thatthebiggertheslipratio,theshorterthelife.Inaddition,thevalueofβincreaseswiththeslipratio.Itcanbeconcludedthatthebiggertheslipratio,thelargerthedispersionofthecompetinglives.
petingfailuremechanismunderrolling-slidingcontact3.3.1.Subsurfaceshearstresses
Itiswidelyacceptedthatthedelaminationfailureofcoatingscausedbysubsurfacecrackingisrelatedtomaximumshearstress(MSS)[9,10].Therefore,therelationbetweenshearstressesandcompetingfailureshouldbeindetaildiscussedbasedontheresultsobtainedbythefiniteelementmethod(FEM).IntheFEMmodel,thethicknessofAT40coatingandthecontactstressweredefinedas400μmand0.75GPa,respectively.Theelasticmodulusofthetestrollerandstandardrollerare173GPaand219GPa,respectively.Poissonsratiosareboth0.3.Thecharacteristicpara-metertodistinguishthecontactconditionswasfrictioncoefficient.Whentheslipratiowas0%,thetestwasunderpurerollingcontactconditionwithoillubricant.Therefore,thefrictioncoefficientundertheslipratioof0%wasdefinedaszero(f1 1/4 0).However,whentheslipratiosaremuchlargerthan0%,thecorrespondingfrictioncoefficientswouldhigherthan0forthefrictioneffectbetweentherollersunderrolling-slidingcontactcondition.Thefrictioncoefficientsweremonitoredbythemeasurementandcontrolsystemofthetestmachine.Theaveragefrictioncoeffi-cientsduringthestablestageunderdifferentslipratios(favg0.082,favgavg
2 1/4 3 1/4 0.097,andf4 1/4 0.118)werechosenasthecharacteristicparametersoftheFEMmodel.
ThedistributionofMSSwithintheAT40coatingunderdiffer-entslipratiosareshowninFig.4.ThepeakvaluesofMSSunderdifferentcontactconditionsalllocatedinsidethecoating.Bothofthepeakvalueandthedistanceofthepeakvaluepositionfromcoating/substrateinterfaceslightlyincreasedwiththeslipratiosincreasing.However,thevaluesofMSSonthecoatingsurfaceunderdifferentslipratiosexhibitedsignificantdifference,asshowninFig.5.ThevaluesofMSSundertheslipratiosofR1 1/4 0%,R2 1/4 25%,R3 1/4 50%,andR4 1/4 75%were0MPa,46
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【图文】Finite element analysis of cracking and delamination of concrete beam due to steel corrosion
Finiteelementanalysisofcrackinganddelaminationofconcretebeamduetosteel
Y.G.Dua,?,A.H.C.Chanb,1,L.A.Clarkb,X.T.Wangc,F.Gurkaloa,S.Bartosd
DepartmentofEngineeringandBuiltEnvironment,AngliaRuskinUniversity,ChelmsfordCM11SQ,UnitedKingdomSchoolofCivilEngineering,TheUniversityofBirmingham,BirminghamB152TT,UnitedKingdomc
DepartmentofCivilEngineering,NingboUniversity,Ningbo,Chinad
FacultyofCivilEngineering,UniversityofZagreb,Zagreb,FranjeHermana16E,Croatia
articleinfoabstract
Thispaperpresentstheanalyticalresultstoinvestigatecrackinganddelaminationofconcretebeamduetosteelcorrosion.Aseriesofconcretebeamswereidealisedastwodimensionalmodelsviatheircrosssectionandanalysedusingthefiniteelementsoftware–LUSAS.Thecorrosionofsteelbarswassimulatedusingaradialexpansion.TheFEresultsshowthatcrackingofbeamsectionduetosteelcorrosioncanbeclarifiedintofourtypes,i.e.,InternalCracking,InternalPenetration,ExternalCracking(HS)andExternalCracking(VB).TheamountofcorrosionintermofradialexpansionrequiredtocausesInternalCracking,InternalPenetration,ExternalCracking(HS)andExternalCracking(VB)variesalmostlinearlywithbardiameterd,barcleardistancesandconcretecoverc,respectively.Iftheratios/cwaslessthanthecriticalvalueofabout2.2,thedelaminationofconcretecovercouldoccurbeforethecrackscanbevisualisedontheconcretesurface,whichdoesconcernengineers.
CrownCopyright?2013PublishedbyElsevierLtd.Allrightsreserved.
Articlehistory:
Received9September2012Revised25February2013Accepted8April2013
Keywords:CorrosionSteelbarCracking
ConcretecoverBarcleardistanceBardiameterBeam
FiniteelementDeteriorationPenetration
1.Introduction
Steelcorrosionisoneofthemostdominantcausesforthepre-maturedegradationofreinforcedconcretestructures.Ithasbeenatopicofwidespreadinteresttothoseconcernedwiththeserviceperformanceandresiduallifeofexistingconcretestructures.Althoughthecollapseofreinforcedconcretestructuresdirectlyasaresultofsteelcorrosionhasrarelybeenreported,maintenanceofthesedeterioratedstructureshasbeenaheavyburdenonown-ersandusersofsuchstructures.
Oneoftheprincipaleffectsofsteelcorrosiononstructuresisthecrackingofconcrete,whichiscausedbythevolumetricexpan-sionofcorrodedsteelbars.Asanelectrochemicalprocessinitiatedbyconcretecarbonationand/orchlorideintrusion,corrosionofasteelbarinconcreteinvolvesbothdissolutionofironionsfrombarsurfaceandtransformationofthedissolvedmetalintocorro-?Correspondingauthor.Tel.:+5.
E-mailaddresses:yingang.du@anglia.ac.uk(Y.G.Du),a.h.chan@bham.ac.uk(A.H.C.Chan),l.a.clark@bham.ac.uk(L.A.Clark),(X.T.Wang),filip.gurkalo@anglia.ac.uk(F.Gurkalo),(S.Bartos).1
sionproducts,i.e.,rusts.Someoftheserustsmaypossiblymigrateintoanyvoidsinsidetheconcrete,andevenpermeatetheconcretecoverandremainontheconcretesurfaceasstains,whichdonotdamagetheintegrityoftheconcrete.However,otherrustsmightaccumulatebetweenthecorrodingbaranditssurroundingcon-crete.Sincetherustsoccupyalargervolumethantheirparentme-tal,aradialexpansionofacorrodingbarwouldtakeplacearounditscircumference,whichcausesahooptensionandradialcom-pressionstrainswithinthesurroundingconcrete.Ascorrosionofasteelbarcontinuesbothhooptensionandradialcompressionstrainsofconcreteincrease.Oncethemaximumtensilestrainoftheconcreteduetoitshoopandradialstrainsexceedsitsdeforma-tioncapacity,cracking,spallingandevendelamination,ofconcretecovercanoccur.
Crackingofconcreteduetosteelcorrosionhassubstantialinflu-encesonperformanceandsafetyofaconcretestructure.Itnotonlyaffectsstructuralaestheticsandserviceability,butalsoacceleratesthecorrosionprocessofsteelbarsbyprovidingampleoxygenandwaterthroughthedevelopedcracks[1],whichinturnpromotesthefurtherdevelopmentofcracksintheconcrete.Inaddition,thecrackingand,inparticular,thedelaminationofconcretecover
/$-seefrontmatterCrownCopyright?2013PublishedbyElsevierLtd.Allrightsreserved.http://dx.doi.org/10.1016/j.engstruct.
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