中文翻译材料Word格式文档下载.docx
- 文档编号:21213621
- 上传时间:2023-01-28
- 格式:DOCX
- 页数:22
- 大小:130.19KB
中文翻译材料Word格式文档下载.docx
《中文翻译材料Word格式文档下载.docx》由会员分享,可在线阅读,更多相关《中文翻译材料Word格式文档下载.docx(22页珍藏版)》请在冰豆网上搜索。
Itwasfoundthatthestressaroundthecracktipisdominatedbyanelasto-plasticsingularstressfield,whichissubstantiallythesameastheelasticsingularstressfieldofaninterfacecrack.
Evaluationofthefracturepathandtoughnesswascarriedoutbasedonthestressintensityfactorsoftheelasto-plasticsingularstressfield.
Keywords
InterfaceCrack,FractureToughness,Si3N4/S45CJoint,ThermalResidualStress,Elasto-plasticAnalysis
Introduction
Theceramic/metaljointshavebeenincreasinglyappliedinawiderangeofengineeringfieldsbecausetheceramichasstablemechanicalpropertiesathightemperatureandgoodresistancetowear,erosionandoxidation.
However,thedifferenceofmaterialpropertiesbetweenmetalandceramicinducesstresssingularitiesattheinterfaceedge.
Moreover,highthermalresidualstresswillbeinducedduringthecoolingprocessduetothemismatchofthethermalexpansioncoefficients.
Thestresssingularitytogetherwiththethermalresidualstressdegradesthestrengthofceramic/metaljointandmakestheevaluationofthestrengthdifficult.
Manyworkshavebeendoneabouttheresidualstressandthestrengthevaluationofceramic/metaljoints.
Forexample,Kobayashietal.[1,2]haveinvestigatedthebendingstrengthandresidualstressofSi3N4/S45Cjointandtheeffectofthesizeofthespecimenonthebendingstrength.
Qiuetal.[3]haveinvestigatedtheinfluenceofresidualstressandcyclicloadonthestrengthofSi3N4/S45Cjoint.
However,duetothecomplexityoftheproblem,ageneralizedevaluationmethodfortheceramic/metaljointhasnotyetbeenproposed.
Theelasticsolutionofthesingularstressfieldoftheinterfacecrackhasbeenstudiedsince1959[4-9].
Rice[10]hassummarizedtheworkinthisfieldandsetuptheelasticfracturemechanicsconceptsforinterfacialcracks.
Yuukietal.[11,12]haveproposedthemaximumnormalstresscriteriaforpredictingfracturepathandstrengthofceramic/metaljointbasedontheelasticplasticdeformationofmetalwillinevitablyappearnearthecracktipduetothestresssingularity.
Formostoftheceramic/metaljoints,theplasticdeformationofmetalhasasignificantinfluenceonthestrengthoftheceramic/metaljoint.
Duetotheanalyticalcomplexity,theevaluationofthefracturepathandstrengthofceramic/metaljointbasedontheelasto-plastictheoryhasnotyetbeenmade.
Inthisstudy,fourpointbendingtestsofSi3N4/S45Cjointspecimenswithaninterfacecrackwerecarriedout.
Evaluationofthefracturepathandfracturetoughnesswasattemptedbasedontheelasto-plasticanalysis.
Experimental
Specimen
Preparation
Figure1showsthegeometryanddimensionsofSi3N4/S45Cjointspecimen.
Thesilverbasedbrazingalloy(wt%is:
Ag,71%,Cu,27%,Ti,2%)with60μmthicknesswasusedforthebondingbetweenSi3N4
ceramicsandS45Csteel.
Brazingwascarriedinavacuumfurnace
Torr).
Thetemperatureofthefurnacewasincreasedatarateof20oC/minuptothebrazingtemperatureof850oCandkeptfor10min,thendecreasedatarateof10oC/min.
Thejoiningsurfaceswerepolishedwithdiamondpowderofμmdiameter.
Duringthebrazing,acontactpressureofMPawasapplied.
Afterbrazing,aninterfacecrackwasintroducedbytheelectricdischargemethodwiththecuttingwireof0.1mmdiameter.
Fourspecimenswithdifferentcracklengthswereprepared.
Twoofthespecimenshadcracklengthsof4.0mmandtheothertwospecimenshadcracklengthsof1.0mmand2.0mm.
Figure1.
Fracturetoughnessspecimen.
ExperimentalResults
Fourpointbendingtestswerecarriedoutonthefracturetoughnessspecimensatacrossheadspeedof0.5mm/min.
Table1showstheresultsofthefracturetoughness.
Theapparentfracturetoughnessisdefinedas:
(1)
with
(2)
(3)
WherePf
isthefractureload,aisthecracklength,wthespecimenwidth,tthespecimenhighness,L2
theouterspanandL1
theinnerspan.
Table1.
Resultofthefracturetoughnesstests.
No.
Cracklengtha(mm)
Pf
(N)
σ
f
(MPa)
FI
KIApparent(MPa√m)
1
2
3
4
AscanbeseeninTable1,thespecimenswithacracklengthof4.0mmindicateahigherfractureloadthanthosewithshortercracklengthsofand2.0mm.
Astheresidualstresswillredistributeaftercutting[2],therelaxationofthermalresidualstressforlongercracklengthmaybeapossiblereason.
Figure2showsthemacroscopicobservationofthefracturedspecimen.
Forthespecimenswithacracklengthofand2.0mm,crackpropagatedintoSi3N4
directlyfromtheinitialcracktipinthedirectionofabout40o.
Forthespecimenswithacracklengthof4.0mm,thecrackpropagatedalongtheinterfaceforabout1.0mmandthenkinkedintoSi3N4
inadirectionofabout10o
totheinterface.
(a)a=1.0mm
(b)a=2.0mm
(c)a=4.0mm
(d)a=4.0mm
Figure2.
Fracturedspecimens.
OscillatorySingularStressFieldofTheInterfaceCrackandTheMaximumNormalStressCriteria
TheelasticsolutionofthestressfieldofaninterfacecrackhasbeenaccomplishedbytheWillims[4],Erdogan[5,6],England[7]andSihetal.[8,9].
Ithasbeenfoundthatthestressfieldneartheinterfacecracktiphastheoscillatorysingularity.
Underthepolarcoordinatewiththeoriginlocatedatthecracktip,thestressfieldcanbeexpressedas
(4)
Here
isthebi-materialconstantthatcanbeexpressedas
(5)
(6)
whereµ
j
and
vj
aretheshearmodulusandthePoisson’sratioofthematerials,respectively.
Thestressintensityfactorsoftheoscillatorysingularstressfieldaredefinedas
(7)
where,
l
isthereferencelengthtoeliminatethedimensionoftheoscillatoryterm.
Usually
takesthevalueofthewholecracklength,.l=2a.
Whenthestressalongtheinterfacehasbeenknown,thestressintensityfactorscanbecanbeextrapolatedas:
(8)
(9)
Yuukietal.[11,12]haveproposedupthemaximumnormalstresscriteriaforthefractureofinterfacecrack.
Consideringthatthevalueof
isverysmall,thenormalstresscanbeapproximatelyexpressedas
(10)
where
(11)
W1=e-ε(π-θ),W2=eε(π+θ)
(12)
(13)
Thedirectionofthemaximumnormalstresscanbedeterminedfrom:
∂B(θ,ε,y)/∂θ=0
(14)
Letθ0
representthedirectionofthemaximumnormalstress,thecorrespondingstressintensityfactorcanbeexpressedas:
(15)
Fracturewilloccuralongthedirectionof
θ0
whenKθmax
reachestheKIC
valueofthebasematerial.
Itshouldbenotedthatfracturemayoccuralongtheinterfacewhen
becomessmallerthancertainvalue,sincethestrengthofinterfaceisusuallylowerthanthatofthebasematerial.
Elasto-PlasticSingularStressFieldatTheInterfaceCrackTip
Theelasto-plasticsingularstressfieldforalinearhardeningmaterial[13]hasbeenfoundtobesubstantiallythesameasthatofelasticmaterialwhoseelasticconstantsaredefinedas:
(16)
whereEistheYoung’smodulusandH’thehardeningcoefficient.
Therefore,theelasto-plasticsingularstressfieldattheinterfacecracktipissubstantiallythesameastheelasticsingularstressfieldoftheinterfacecracktip.
Thegoverningregionoftheelasto-plasticsingularstressfieldwillbeconfinedinasmallregionaroundthecracktipinsidetheyieldzone.
Forceramic/metaljoint,consideringthatthevalueofhardeningcoefficientismuchlessthanthevalueofYoung’smodulus,itcanbefoundfromEq.(16)andEq.(5)that
(17)
FEMAnalysisandEvaluationofFracturePathandToughnessBasedontheElasto-PlasticStressIntensityFactors
FEManalysiswascarriedoutunderplanestressconditionusingtheprogramofABAQUS.
Si3N4
isassumedasanelasticmaterialwhosematerialconstantsareindependentoftemperatureandE=289GPa,
v=andCTE=.
S45CsteelisassumedasalinearhardeningmaterialwiththematerialconstantslistedinTable2[14].
Thestressfreetemperatureisconsideredtobe550oCfortheanalysisofthethermalresidualstress.
Table2.
MaterialconstantsofS45C
25oC
100oC
200oC
300oC
400oC
500oC
600oC
E
(GPa)
206
201
197
192
187
183
v
σY-
375
348
333
309
280
241
193
H’(MPa)
1381
2056
2680
2325
1685
1026
687
CTE(10-6)
Forcomparison,theelasticanalysiswasalsocarriedout.
Calculatedfromtheelasticconstantsof25oC,thebi-materialconstant
forelasticcaseis.
Table3liststhestressintensityfactorsaswellasthedirect
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- 中文翻译 材料
![提示](https://static.bdocx.com/images/bang_tan.gif)