工程力学专业英语阅读.ppt

专业英语阅读,工程力学专业,CourseArrangement,Presentation,Startfrom3rdclass,2presentationseachtimeGroupworkrequired4-5peopleineachgroup,12groupsintotalIneachgroup,i.e.someresponsibleforthepresentation,someresponsibleforansweringquestionsInvolvementfromaudiencewillearnextracreditsOrderofpresentationscouldbevolunteeredorspecifiedReferencerated,PresentationFlow,IntroduceyourselfIntroduceyourtopicandtheauthorsofthepaperName,university/institute,yearpublished,journalpublishedProvideanoutlineofthewholepresentationOroduction,experimental/simulationprocedure,results,discussion,conclusionBackgroundoftheproblemstudiedMethodology:howtostudytheproblemConclusionsobtained,SampleOutline,MotivationImportanceofcelladhesionExistingcelladhesionmeasurementtechniquesLaser-inducedstresswavetechniqueExperimentalSetupSamplePreparationExperimentalResultsObservationofcelldecohesionQuantitativeadhesionmeasurementConclusionandDiscussion,Requirements,EnglishspeakingChineseexplanationTrytohavemoregraphicsthansentencesontheslidesNotesareallowedduringthepresentation,最多三人讲，一共15分钟，不可超时页面上满页的文字不允许，要通过自己讲解主要基于文章的内容，可扩展，不可删减可使用卡片，记录要点,Mechanics,TheoreticalMechanics理论力学MaterialMechanics材料力学CompositeMaterialsMechanics复合材料力学FluidMechanics流体力学StructureMechanics结构力学FractureMechanics断裂力学ElasticMechanics弹性力学ContinuumMechanics连续介质力学QuantumMechanics量子力学,MechanicalSimulations:Solid,Fluid;BioMechanics;SoilMechanics;ArchitecturalMechanics.,Topics,EngineeringSimulations工程计算ExperimentalMechanics力学实验BioMechanics生物力学MaterialMechanics材料力学SmallScaleMechanics微尺度力学FluidMechanics流体力学,FrequentlyUsedWords,Units(单位)：Distance:kilo-meter(km),meter(m),milli-meter(mm),micro-meter(mm),nano-meter(nm),pico-meter(pm)inch,foot,mileTime:second(s),minute(m),hour(h),day,yearmilli-second(ms),micro-second(ms),nano-second(ns),pico-second(ps),femto-second(fs),atto-second(as)Temperature:degreecentigrade(),Fahrenheit(F),Kelvin(K)Force:Newton(N),Stress:Pascal(Pa),mega-Pascal(MPa),giga-Pascal(GPa)bar,torr,atmosphere(atm)Strain,Prefixsupersonic;superposition;supercomputerMethodmethodologySolidsolidifyMechanicsmechanicalBiomechanicsmechatronicsmechanismmechanicalismmechanicallyfoamedplastic,Example:,MechanicalBehaviorofMaterials,MechanicalBehaviorofMaterials,byThomasH.CourtneyOriginaleditionpublishedin1990inUSPhotocopiesavailablein2004inChina,Outline,ElasticdeformationPermanentdeformationThetensiontestStrain-ratesensitivityYieldingundermultiaxialloadingconditionsMohrscircleThehardnesstestThetorsiontest,FractureFracturetoughnessTensilefractureCreepfractureFatiguefractureEmbrittlementSummary,Section1.1Introduction,Thisbookdealswiththemechanicalbehaviorofsolids,particularlyasthisbehaviorisaffectedbyprocessestakingplaceatthemicroscopicand/oratomiclevel.Theresponseofasolidtoexternalorinternalforcescanvaryconsiderably,dependingonthemagnitudeoftheseforcesandthematerialcharacteristics.Forexample,iftheforcesaregreatthematerialmayfracture.Lesservaluesofforcemayresultinmaterialpermanentdeformationwithoutfractureand,iftheforcesarelowenough,thematerialmaydeformonlyinanelasticway.Thetreatmentofmechanicalbehaviorinthisbookcloselyparallelsthesethreepossibilities.,Al5%-Cualloy:coolingrate10/s,Al5%-Cualloy:coolingrate1/s,SomeImportantWords,Fracture断裂Elasticdeformation弹性变形Externalforce外力Internalforce内力,Microscopic微观Atomiclevel原子水平Magnitude幅值Force力Permanentdeformation永久变形,Whileouraimistorelatethemechanicalbehaviorofasolidtomaterialstructureatthemicroscopicandatomiclevel,thisresponseismanifestedmacroscopically.Thus,tofulfilladequatelytheobjectiveofthistext,areasonablebackgroundintheconceptsofmechanicalbehaviorasmeasuredandassessedatamacroscopiclevelisrequired.Indeed,itisthiscouplingbetweenmaterialmicrostructureandbulkpropertiesthatconstitutesoneofthemostfruitfulareasofmaterialsscienceandengineering.,SomeImportantWords,Macroscopic宏观microscopic微观Coupling耦合Microstructure微观结构Bulkproperties整体性质,Section1.2ElasticDeformation,Whenasolidissubjectedtoexternalforces,itundergoesachangeinshape.Whentheloadisreleased,theshapemaynotreturnedtowhatiswaspriortotheapplicationoftheforce;underthesecircumstanceswesaythatthematerialhasdeformedpermanently.Forceslessthanthosethatcausepermanentdeformationdeformthesolidelastically;thatis,whentheforceissubsequentlyremovedthebodyassumesthedimensionsithadpriortoitsapplication.,TheelasticbehaviorofmanymaterialscanberepresentedbyaformofHookeslaw.,Theextensionofasampleislinearrelatedtotheforce.Theextensionalsodependsonsampledimensions.Forexample,doublingofinitialsamplelengthleadstoadoublingoftheextension,whereasifthesamplecross-sectionalareanormaltotheappliedforceisdoubled,theextensionishalved.,SomeImportantWords,Extension伸长externalforce外力Cross-sectionalarea横截面积Normal法向，normalto垂直,perpendicularParallel平行,Thisequationisoftenwritteninnormalizedformofstressandstrain,withEtheYoungsmodulusortensilemodulus.Amaterialhavingahighvalueofthetensilemodulusisstiff;i.e.,itisresistanttotensiledeformationofthekindjustdescribed.Linearelasticityofthiskindisobservedinallclassesofsolids.Itisthedominantmodeofelasticdeformationinallsolidsatlowtemperatures,incrystallinesolidsandinorganicglassesuptomoderatelyhightemperatures,andinnoncrystallinepolymersatlowtemperatures.Theextentoflinearelasticityisusuallyquitelimited;thatis,mostmaterialsarecapableofbeinglinearlyelasticallyextendedonlytostrainsontheorderofseveraltenthsofapercent.Linearelasticityrepresentsthestretching(orcompression/distortion)ofatomicbonds,andforthisreasonEisameasureofamaterialsbondstrength.,SomeImportantWords,Normalize归一化Tensilemodulus拉伸模量；Youngsmodulus杨氏模量Tensiletest拉伸实验Stiff硬；stiffness硬度crystallinesolid晶体Inorganicglass无机玻璃noncrystallinepolymers非晶态聚合物Stretching/compression/distortion拉伸/压缩/扭曲Atomicbonds原子键,Achangeinmaterialshapecanalsobecausedbyshearstresses.Thesecauserelativedisplacementoftheupperandlowersurfacesofthesolidillustrated.Theshearstrainandshearstressarerelatedthrough,withGtheshearmodulus.,InaphysicalsenseGcanbeviewedasameasureoftheresistancetobonddistortionwithinasolid.Thiscanbevisualizedbyconsideringthesimple-cubicsinglecrystal.Thechangeinatomicpositionsduetotheshearstressresultsfrom“bending”ofatomicbonds.,SomeImportantWords,Shearstress剪切应力Shearstrain剪切应变Relativedisplacement相对位移Position位置,Almostallclassesofsolidsalsoexhibit,atleastoveracertaintemperaturerange,nonlinearandtime-dependentelasticity.Thisviscoelasticity,asitiscalled,ismostcommontononcrystallinepolymers,butalsooccurstoamuchmorelimitedextentincrystallinesolidsandinorganicglasses.,Thestraininalinearelasticsolidisasingle-valuedfunctionofthestress;thatis,theloadingandunloadingsegmentsofthe-relationshipinaviscoelasticmaterialdependsonthesenseofloading.Moreover,thelevelofstressattaineddepends,too,ontherateatwhichaviscoelasticmaterialisstretched(thestrainrate).Withincreasingstrainrateaviscoelasticmaterialbecomesstiffer;forexample,the“average”modulus(1/1)increaseswithstrainrate.Viscoelasticbehaviorisalsomanifestedbyastrainthatvarieswithtimeunderconditionsofaconstantappliedstress.Thatis,uponinitialapplicationofthestresssomeinstantaneous(linearelastic)strainisfirstexperienced,followingwhichthematerialcontinuetoextend,withthestrainapproachingsomeasymptoticvalue.Onremovaloftheload,thelinearelasticstrainisinstantaneously,andtheviscoelasticstrainsluggishly,recovered.,SomeImportantWords,Viscoelasticity粘弹性Single-valuefunction单值函数Loading/unloading加载/缷载Strainrate应变率Linearelastic线弹性,Nonlinearelasticity,ofwhichviscoelasticityisoneexample,neednotbetime-dependent.Forexample,nonlineartime-independentelasticityisobservedincertainfine,strongcrystallinesolidscalledwhiskers.Whiskerstypicallyhavediametersontheorderofmicrometers,andwhenstretchedintensiontheydeforminalinearelasticwayuptostrainsontheorderofhalfapercent.Forelasticstrainsinexcessofthis(whiskersarecapableofsuchstrains)the-relationshipisnonlinear.Anextremeexampleofnonlineartime-independentelasticityisfoundinelastomers.Theseareaspecialclassofpolymersthatoveralimitedtemperaturerangearecapableofdemonstratingextensiveelasticstrains(uptoathousandpercentorso).Thisrubberelasticityisquitedifferentfromlinearelasticity,whichisasmentioned,ordinarilylimitedand,asmightbeexpected,thecausesofrubberelasticitydifferfundamentallyfromthoseoflinearelasticity.,SomeImportantWords,Whisker须晶Elastomer高弹性体，人造橡胶Rubber橡胶,SomeImportantWords,Fracture断裂Elasticdeformation弹性变形Externalforce外力Internalforce内力,Microscopic微观Atomiclevel原子水平Magnitude幅值Force力Permanentdeformation永久变形,SomeImportantWords,Macroscopic宏观microscopic微观Coupling耦合Microstructure微观结构Bulkproperties整体性质,SomeImportantWords,Normalize归一化Tensilemodulus拉伸模量；Youngsmodulus杨氏模量Tensiletest拉伸实验Stiff硬；stiffness硬度crystallinesolid晶体Inorganicglass无机玻璃noncrystallinepolymers非晶态聚合物Stretching/compression/distortion拉伸/压缩/扭曲Atomicbonds原子键,SomeImportantWords,Shearstress剪切应力Shearstrain剪切应变Relativedisplacement相对位移Position位置,SomeImportantWords,Viscoelasticity粘弹性Single-valuefunction单值函数Loading/unloading加载/缷载Strainrate应变率Linearelastic线弹性,SomeImportantWords,Whisker须晶Elastomer高弹性体，人造橡胶Rubber橡胶,Section1.3PermanentDeformation,Amaterialsresponsetouniaxialloadingisassessedmostoftenbymeansofatensiontest.Forceismeasuredwithaloadcell(oftenacalibrated,stiffspring);extensionismeasuredbyextensometer.Somematerials(brittleones)manifestonlymacroscopicelasticdeformationuptothestressatwhichtheyfracture.Examplesincludeinorganicglasses,polycrystallineceramicsatroomtemperature,andsomemetalsandtheiralloysatlowtemperatures.Mostmetalsatordinarytemperatures,andmanyceramicsathightemperatures,deformpermanentlybeforefracture.,36,s,o,y,k,e,elastic,yield,workharden,necking,T.S.,SomeImportantWords,Loadcell测压元件Calibrate标定Extensometer变形测定器;张量计Brittle脆性Polycrystalline多晶材料Metalsandalloys金属及合金,SomeImportantWords,Extension伸长externalforce外力Cross-sectionalarea横截面积Normal法向，normalto垂直,perpendicularParallel平行,Section1.3PermanentDeformation,39,s,o,y,k,e,elastic,yield,workharden,necking,T.S.,SomeImportantWords,Workhardening应变强化Truestress真实应力Engineeringstress工程应力,Engineeringstrainbydefinitionisoverestimated.Truestrainisbasedoninstantaneoussamplelength.Itcanbeapproximatedbyconsideringthetotalstraintoresultfromaseriesofsmall,incrementalextensions.,Expressindifferentialform,Integratefroml0toli,Theconstant-volumeconditionofplasticdeformationallowsrelationshipstobedevelopedamongstressandstrain,ForatensiletestForcompressiontest,therelationwillbeoppositeThedifferencebetweenthetrueandengineeringstressesandstrainsincreaseswithplasticdeformation.Thus,atlowstrains,soindiscussionofelasticdeformation,thereisnoneedtodifferentiatebetweenengineeringandtruestressandstrain.,Thetensilepointisassociatedwithageometricalinstability,andnotwithafundamentalalterationinmaterialbehavior.Eachandeverytensilebarhasinhomogeneitiesalongitslength;eitherwithinit(e.g.smallinclusionsorporosity)oronitssurface(e.g.machiningmarksorataperalongthebarsurface).Strainislocalizedintheseregions,andthisleadstoalocallygreaterreductioninarea.Forstrainslessthanthetensilepoint,theincreaseinflowstress,accompanyingthegreaterstrainsislargeenoughtoleadtoremovaloftheincipientinstability.Thisprocessoccursregularlyandrepeatedlyduringtensileloading,andcouldbemonitoredifsufficientlyaccurateinstrumentationwereavailable.Therateofworkhardeningdecreasesasdeformationcontinues;thatis,theincreaseinflowstressperunitstrainbecomeslesswithincreasingstrain.Thus,itbecomesprogressivelymoredifficulttoworkhardenanincipientinstabilitysufficientlytoremoveit.Asthetensilepoint,thework-hardeningcapacityhasbeendiminishedenoughthataninstabilityonceformedcontinuestodevelop.,Thecriterionforneckingisrelatedtothematerialsworkhardeningtendenciesv.s.thosethatinitiateinstability.ThecriterioncanbeexpressedquantitativelybyrealizingthatatT.S.theengineeringstressorequivalently,theforcereachesamaximum,Anothermeasureofmaterialductilityisreductioninareaatfracture,usuallyexpressedaspercentR.A.Thefinalcross-sectionalareaismeasuredastheareaoftheneckfollowingfracture.Since%R.A.isindependentofsamplegagelength,itismoreofamaterialpropertythanpercentelongation.Asaresultofthenonuniformdeformationfollowingtheonsetofnecking,truestressandstraincannotbecalculatedfromengineeringstressandstrain.However,truestresscanstillbedefinedastheforcedividedbytheinstantaneousarea,providedthelatteristakenastheminimumcross-sectionalarea.Somecaremustbetakenwhendoingthis,particularlyatthelaterstagesofneckdevelopmentandatstrainsclosetothefracturestrain.Awell-developedneckaltersthestressstateintheneckregionfromthatofsimpletension.,Words,Nonuniform不均匀Onset开始初始,TheeffectisthatT=F/Aneckbecomesonlyanapproximation.Additionally,internalvoids,whichareprecursorstofracture,forminthelaststagesofatensiletest,andthisleadstoanunderestimateofTwhenitiscalculatedintheaboveway.Byconsideringtheneckasthedeformingvolume,truestraincanalsoberedefinedfollowingnecking.Beforenecking,T=ln(li/l0)(orequivalently,T=ln(Ai/A0).Followingnecking,itisdefinedonlyonanareabasis,thatis,bythelatterexpressionwithAitakenastheneckarea.Becauseconfusionoftenarisesaswhentheyarenot,Table1.1synopsizesengineeringantruedefinitionsofstressandstrain,andexpressionforthemappropriatetotensileflowbeforeandafterneckingarealsolistedthere.,Words,Nonuniform不均匀Onset开始初始Precursor预示Redefine重新定义,Agraphoftruestress-truestraindoesnotdemonstrateanythingunusualattensilestrength(Fig.1.9).Thisisadditionalevidencethatneckingisgeometricinoriginanddoesnotreflectchangesinmaterialproperties.Onefinalpointisinorder.Wehavementionedthat,priortonecking,T0)theyieldyieldconditionisunaffectedbytheminortensilestress.Forexample,ifweinitiallyhaveastressstate10,2=3=0,andthenincrease2,theyieldconditionremains1=ysolongas12.thissomewhatunexpectedresultisatvariancewithexperimentalstudies,asisshownlater.Indeed,adifferentyieldcriterion,thevonMisesone,whichpredictsthatyieldinginthefirstquadrantisafunctionofboth1and2isgenerallymoreaccuratethantheTrescaoneforpredictingyieldingundermultiaxialstressstates.,ThevonMisesyieldcriterionisexpressasTheconditionstatesthatyieldingwillnottakeplaceforprincipalstresscombinationssuchthattheleft-handsideoftheaboveequationislessthaty.TheyieldlocusunderbiaxialloadingforthevonMisesconditionisillustratedinFig.1.11b.Weseethatitisanellipseinthe1,2plane,andthevonMisesandtheTrescaconditionsareequivalentonlyforuniaxialloading(10,2=3=0or20,1=3=0)andbalancedbiaxialloading(1=2,3=0).Asnoted,theyieldlociofFigs.1.11areappropriatetoasituationwhereoneoftheprincipalstressesiszero.BoththeTresaandVonMisesyieldcriteriaalsoapplytothesituationwherethisisnotthecase.,Whenthisisso,thecriteriacanbegraphicallydisplayedinthree-dimensionalprincipalstressspace.ThevonMisesyieldlocustheniscylindricalinshapewiththeaxisofthecylinderlyingalongthe111inprincipalstressspace.Thus,whenthiscylinderis“sliced”alongthe3=0plane,anellipseisfound.Similarly,theTrescayieldsurfaceisaregularhexagontranslatedalongthe111directioninprincipalstressspace.Whenthisshapeissectionedalongthe3=0plane,thedistortedhexagondisplayedinFig.11aisobserved.Finally,wenotethatthethree-dimensionalTrescayieldsurfaceisinscribedwithinthevonMisesone,touchingthelatteratthehexagonvertices.,AnumberofideashavebeensetforthattemptingtorationalizethevonMisesconditiononfundamentalgrounds.However,itisessentiallyanempiricalcriterionthatnonethelessmoreaccuratelydescribesyieldingundermultiaxialstressstatesthandoestheTrescacondition.ThisisshowninFig.1.11c,inwhichresultsobtainedfrombiaxialyieldingstudiesareshown.The