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外文翻译--Si3N4S45C的断裂韧性界面裂纹.doc外文翻译--Si3N4S45C的断裂韧性界面裂纹.doc -- 5 元

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1FractureToughnessofSi3N4/S45CJointwithanInterfaceCrackLiedongFu,YukioMiyasitaandYoshiharuMutohCopyrightADTECH.licenseeAZoM.comPtyLtd.ThisisanAZoOpenAccessRewardsSystemAZoOARSarticledistributedunderthetermsoftheAZo–OARShttp//www.azom.com/oars.aspwhichpermitsunrestricteduseprovidedtheoriginalworkisproperlycitedbutislimitedtononcommercialdistributionandreproduction.PostedSeptember2005TopicsCoveredAbstractKeywordsIntroductionExperimentalSpecimenPreparationExperimentalResultsOscillatorySingularStressFieldofTheInterfaceCrackandTheMaximumNormalStressCriteriaElastoPlasticSingularStressFieldatTheInterfaceCrackTipFemAnalysisandEvaluationofFracturePathandToughnessBasedontheElastoPlasticStressIntensityFactorsConclusionsReferencesContactDetailsAbstractFracturetoughnesstestswerecarriedoutforSi3N4/S45Cspecimenswithinterfacecracksofdifferentlengths.Itwasfoundthatthespecimenwithacrackof4mmhashigherapparentfracturetoughnessthanthosewithcracksof1mmand2mmduetothereductionoftheresidualstress.FracturepropagatedintoSi3N4fromthecracktipinthedirectionof40oforcracksof1mmand2mmwhileitpropagatedalongtheinterfaceforcrackof4mm.ElastoplasticanalysiswascarriedoutconsideringS45CasthelinearhardeningmaterialandSi3N4astheelasticmaterial.Itwasfoundthatthestressaroundthecracktipisdominatedbyanelastoplasticsingularstressfield,whichissubstantiallythesameastheelasticsingularstressfieldofaninterfacecrack.Evaluationofthefracturepathandtoughnesswascarriedoutbasedonthestressintensityfactorsoftheelastoplasticsingularstressfield.KeywordsInterfaceCrack,FractureToughness,Si3N4/S45CJoint,ThermalResidualStress,ElastoplasticAnalysisIntroductionTheceramic/metaljointshavebeenincreasinglyappliedinawiderangeofengineeringfieldsbecausetheceramichasstablemechanicalpropertiesathightemperatureandgoodresistancetowear,erosionandoxidation.However,thedifferenceofmaterialpropertiesbetweenmetalandceramicinducesstress2singularitiesattheinterfaceedge.Moreover,highthermalresidualstresswillbeinducedduringthecoolingprocessduetothemismatchofthethermalexpansioncoefficients.Thestresssingularitytogetherwiththethermalresidualstressdegradesthestrengthofceramic/metaljointandmakestheevaluationofthestrengthdifficult.Manyworkshavebeendoneabouttheresidualstressandthestrengthevaluationofceramic/metaljoints.Forexample,Kobayashietal.1,2haveinvestigatedthebendingstrengthandresidualstressofSi3N4/S45Cjointandtheeffectofthesizeofthespecimenonthebendingstrength.Qiuetal.3haveinvestigatedtheinfluenceofresidualstressandcyclicloadonthestrengthofSi3N4/S45Cjoint.However,duetothecomplexityoftheproblem,ageneralizedevaluationmethodfortheceramic/metaljointhasnotyetbeenproposed.Theelasticsolutionofthesingularstressfieldoftheinterfacecrackhasbeenstudiedsince195949.Rice10hassummarizedtheworkinthisfieldandsetuptheelasticfracturemechanicsconceptsforinterfacialcracks.Yuukietal.11,12haveproposedthemaximumnormalstresscriteriaforpredictingfracturepathandstrengthofceramic/metaljointbasedontheelastictheory.Theplasticdeformationofmetalwillinevitablyappearnearthecracktipduetothestresssingularity.Formostoftheceramic/metaljoints,theplasticdeformationofmetalhasasignificantinfluenceonthestrengthoftheceramic/metaljoint.Duetotheanalyticalcomplexity,theevaluationofthefracturepathandstrengthofceramic/metaljointbasedontheelastoplastictheoryhasnotyetbeenmade.Inthisstudy,fourpointbendingtestsofSi3N4/S45Cjointspecimenswithaninterfacecrackwerecarriedout.Evaluationofthefracturepathandfracturetoughnesswasattemptedbasedontheelastoplasticanalysis.ExperimentalSpecimenPreparationFigure1showsthegeometryanddimensionsofSi3N4/S45Cjointspecimen.ThesilverbasedbrazingalloywtisAg,71,Cu,27,Ti,2with60μmthicknesswasusedforthebondingbetweenSi3N4ceramicsandS45Csteel.Brazingwascarriedinavacuumfurnace2.5x105Torr.Thetemperatureofthefurnacewasincreasedatarateof20oC/minuptothebrazingtemperatureof850oCandkeptfor10min,thendecreasedatarateof10oC/min.Thejoiningsurfaceswerepolishedwithdiamondpowderof0.25μmdiameter.Duringthebrazing,acontactpressureof0.002MPawasapplied.Afterbrazing,aninterfacecrackwasintroducedbytheelectricdischargemethodwiththecuttingwireof0.1mmdiameter.Fourspecimenswithdifferentcracklengthswereprepared.Twoofthespecimenshadcracklengthsof4.0mmandtheothertwospecimenshadcracklengthsof1.0mmand2.0mm.3Figure1.Fracturetoughnessspecimen.ExperimentalResultsFourpointbendingtestswerecarriedoutonthefracturetoughnessspecimensatacrossheadspeedof0.5mm/min.Table1showstheresultsofthefracturetoughness.Theapparentfracturetoughnessisdefinedas1with23WherePfisthefractureload,aisthecracklength,wthespecimenwidth,tthespecimenhighness,L2theouterspanandL1theinnerspan.Table1.Resultofthefracturetoughnesstests.No.CracklengthammPfNσfMPaFIKIApparentMPa√m11.0285.417.1281.04360.980722.0237.814.271.05301.160734.01649.098.951.256112.431744.01744.2104.651.256113.1478AscanbeseeninTable1,thespecimenswithacracklengthof4.0mmindicateahigherfractureloadthanthosewithshortercracklengthsof1.0and2.0mm.Astheresidualstresswillredistributeaftercutting2,therelaxationofthermalresidualstressforlongercracklengthmaybeapossiblereason.Figure2showsthemacroscopicobservationofthefracturedspecimen.Forthespecimenswithacracklengthof1.0and2.0mm,crackpropagatedintoSi3N4directlyfromtheinitialcracktipinthedirectionofabout40o.Forthespecimenswithacracklengthof4.0mm,thecrackpropagatedalongtheinterface4forabout1.0mmandthenkinkedintoSi3N4inadirectionofabout10ototheinterface.aa1.0mmba2.0mmca4.0mmda4.0mmFigure2.Fracturedspecimens.OscillatorySingularStressFieldofTheInterfaceCrackandTheMaximumNormalStressCriteriaTheelasticsolutionofthestressfieldofaninterfacecrackhasbeenaccomplishedbytheWillims4,Erdogan5,6,England7andSihetal.8,9.Ithasbeenfoundthatthestressfieldneartheinterfacecracktiphastheoscillatorysingularity.Underthepolarcoordinatewiththeoriginlocatedatthecracktip,thestressfieldcanbeexpressedas4Hereisthebimaterialconstantthatcanbeexpressedas56whereµjandvjaretheshearmodulusandthePoissonsratioofthematerials,respectively.Thestressintensityfactorsoftheoscillatorysingularstressfieldaredefinedas
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