雙語課后題答案

WhatisManufacturing?WhatproductsdoesManufacturingmayproduce?Manufacturing,initsbroadestsense,istheprocessofconvertingrawmaterialsintoproducts;itencompassesthedesignandmanufacturingofgoodsusingvariousproductionmethodsandtechniques.Manufacturingmayproducediscrete（離散的）products,meaningindividualpartsorpieces,suchasnails,rivets,gears,steelballs,andbeveragecans（飲料罐）.Ontheotherhand,wire,sheetmetal,tubing,andpipearecontinuousproductsthatmaybecutintoindividualpiecesandthusbecomediscreteproducts.Manufacturingisreallyimportantfornationalandglobaleconomies.Pleasestatesomereasonsaboutthisdescriptionfromyourpointsofview.Manufacturingactivitiesmustberesponsivetoseveraldemandsandtrends.Pleasediscussthespecificdemandsandtrendsincludedinthemanufacturingactivities.Aproductmustfullymeetdesignrequirementsandspecificationsandstandards.Bemanufacturedbythemosteconomicalandenvironmentallyfriendlymethods.Qualitymustbebuiltintotheproductateachstage.Productionmethodsmustbesufficientlyflexibletorespondtochangingmarketdemands.Newdevelopmentsinmaterials,productionmethods,andcomputerintegration.Manufacturingactivitiesmustbeviewedasalargesystem,eachpartofwhichisinterrelated.Workwiththecustomertogettimelyfeedbackforcontinuousproductimprovement.Constantlystriveforhigherproductivity,optimumuseofallitsresources.PleasedescribetheconceptofProductDesignusingyourstatements.ProductDesignisacriticalactivitybecauseithasbeenestimatedthat,generally,70to 80%ofthecostofproductdevelopmentandmanufactureisdeterminedattheinitialdesignstages.PleaseexplaintheconceptofConcurrentEngineeringusingyourstatements.Concurrentengineering,alsocalledsimultaneousengineering,isasystematicapproachintegratingthedesignandmanufactureofproductswiththeviewtowardoptimizingallelementsinvolvedinthelifecycleoftheproduct.Thebasicgoalsofconcurrentengineeringaretominimizeproductdesignandengineeringchanges,aswellasthetimeandcostsinvolvedintakingtheproductfromdesignconcepttoproductionandintroductionoftheproductintothemarketplace.HowmanystagesareincludedintheprocessofComputer-aideddesign （CAD）?analyticalandphysicalmodelsselectandspecifythefinalshapeandthedimensions,dimensionaltolerancesandsurfacefinishoftheparts,andmaterialstobeusedcomputersimulationsmakeandtestaprototype,rapidprototypeappropriateprocessplans,manufacturingmethods,equipment,andtoolingareselectedWhatistheVirtualPrototyping?Virtualprototype（虛擬原型）isasoftwareformofprototypingandusesadvancedgraphicsandvirtual-realityenvironmentstoallowdesignerstoexamineapart.Inaway,thistechnologyisusedbyCADpackagestorender（渲染）apartsothatdesignerscanobserveandevaluatethepartasitisdrawn.Pleaseexplaintheconceptsofdesignforassembly（DFA）,designfordisassembly（DFE）anddesignformanufacturingandassembly（DFMA）.Assemblyisanimportantphaseoftheoverallmanufacturingoperationandrequiresconsiderationsoftheease,andcostofputtingpartstogether.Productmustbedesignedsothatdisassemblyispossiblewithrelativeeaseandrequirelittletime,enablingtheproducetobetakenapartformaintenance（維護(hù)），servicing,orrecyclingoftheircomponents.Becauseassemblyoperationscancontributesignificantlytoproductcost,designforassembly（DFA）anddesignfordisassemblyareimportantaspectofmanufacturing.Designforserviceisanotherimportantaspect,ensuringthatindividualpartsinaproductareeasytoreachandservice.Theseactivitiesarenowcombinedintodesignformanufactureandassembly （DFMA）,whichrecognizetheinherent（固有的）andimportantinterrelationshipsamongdesign,manufacturingandassembly.PleasesummarytheDesignprinciplesforeconomicproductionincludedinthemodernindustrialmanufacturingprocesses.Designprinciplesforeconomicproductionmaybesummarizedasfollows:1） Designshouldbeassimpleaspossibletomanufacture,assemble,disassemble,service,andrecycle.2） Materialsshouldbechosenfortheirappropriatedesignandmanufacturingcharacteristicsaswellasfortheirservicelife.3） Dimensionalaccuracyandsurfacefinishspecifiedshouldbeasbroadaspermissible（固有）.4） Becausetheycanaddsignificantly（顯著）tocost,secondaryandfinishingoperationsshouldbeavoidedorminimized.PleaseexplaintheconceptofProductLifeCycle（PLC）.WhatfivestagesareincludedintheProductLifeCycle（PLC）?ProductLifeCycleconsistsofthestagesthataproductgoesthrough,fromdesigndevelopment,distribution,anduse,toitsultimatedisposalandrecycling.Aproducttypicallygoesthroughfivestages.1.Productdevelopmentstage,involvingmuchtimeandhighcosts.Marketintroductionstage,inwhichtheacceptanceoftheproductinthemarketplaceiscloselywatched.Growthstage,withincreasingsalesvolume,lowermanufacturingcostperunit,andhencehigherprofitabilitytothemanufacturing.Maturationstage,wheresalesvolumebeginstopeakandcompetitiveproductsbegintoappearinthemarketplace.Declinestage,withdecreasingsalesvolumeandprofitability.Howmanytypesofmaterialsdoyouknowaregenerallyusedinmanufacturingtodayindustrialfields?Thetypesofmaterialsgenerallyusedinmanufacturingtodayare:1） Ferrousmetals:carbonsteels,alloysteels,stainlesssteels,andtoolanddiesteels.2） Nonferrousmetalsandalloys（有色金屬禾口合金）:aluminum,magnesium（Mg）,copper,nickel,superalloys,titanium,refractorymetals（耐火才材料）（molybdenum,niobium,tungsten,andtantalum）,beryllium（鍍），zirconium（錯(cuò)），low-meltingalloys（lead,zinc,andtin）,andprecious（珍貴的）metals.3） Plastics:thermoplastics,thermosets（熱固性塑料）andelastomers（彈性體）.4）Ceramics:glassceramics,glasses,graphite（石墨），anddiamond.5） Compositematerials:reinforcedplastics（增強(qiáng)塑料），metal-matrix（金屬矩陣）andceramicmatrix（陶瓷組成）composites,andhoneycombstructures;thesearealsoknownasengineeredmaterials.6） Nanomaterials（納米材料），shape-memoryalloys（形狀記憶合金），metalfbams（金屬泡沫材料)，amorphousalloys(ME晶合金),super-conductors(超導(dǎo)體),andsemiconductors(半導(dǎo)體).Howmanyprocessingmethodsformaterialscanbeusedinmanufacturingtodayindustrialfields?Howtoselectthemanufacturingprocessesformaterials.Thebroadcategoriesofprocessingmethodsformaterialscanbelistedasfollows:1) Casting:Expendablemoldingandpermanentmolding.Formingandshaping:Rolling,forging,extrusion,drawing,sheetforming,powermetallurgy,andmolding.3)Machining:Turing,boring,drilling,milling,planning,shaping,broaching,grinding,ultrasonicmachining;chemical,electrical,andelectrochemicalmachining;andhigh-energybeammachining.Joining:Welding,brazing,soldering,diffusionbonding,adhesivebonding,andmechanicaljoining.MicromanufacturingandNanomanufacturing:Surfacemicromachining,dryandwetetching,andelectrofbrming.Finishing:Honing,lapping,polishing,burnishing,deburring,surfacetreating,coating,andplating.Selectionofaparticularmanufacturingprocess,oraseriesofprocesses,dependsnotonlyonthecomponentorpartshapetobeproduced,butalsoonmanyotherfactors.Forexample,brittleandhardmaterialscannoteasilybeshapedwhereastheycanbecastormachinedbyvariousmethods.Themanufacturingprocessusuallyaltersthepropertiesofmaterials;metalsthatareformedatroomtemperature,forexample,becomestronger,harder,andlessductilethantheywerebeforeprocessing.Thus,characteristicssuchascastability,formability,machinability,andweldabilityofmaterialshavetobestudied.PleasediscusstheconceptofNet-shapemanufacturing.Whyshouldthepeopledeveloptheconceptofnet-shapeornear-net-shapemanufacturingtoday?Net-Shapemanufacturing:Becausenotallmanufacturingoperationsproducefinishedpartsorproductstodesiredspecifications,additionalfinishingoperationsmaynenecessary.Forexample,aforgedpartmaynothavethedesireddimensionalaccuracyorsurfacefinishthusadditionaloperationssuchasmachiningorgrindingmaybenecessary.Itmaybedifficult,impossible,oruneconomicaltoproducebyusingonlyonemanufacturingprocessapartthat,bydesign,hasanumberofholesinit,necessitatingadditionalprocessedsuchasdrilling.Consequently,net-shapeornear-net-shapemanufacturinghasbecomeanimportantconceptinwhichthepartismadeasclosetothefinaldesireddimensions,tolerances,andspecificationsaspossible.Computershaveverysignificantimpactonmanufacturing.Pleasegiveanoutlineofthemajorapplicationsofcomputersinmanufacturingtoday?Thefollowingisanoutlineofthemajorapplicationsofcomputersinmanufacturing:1)Computernumericalcontrol(CNC).2)Adaptivecontrol(AC).Industrialrobots(工業(yè)機(jī)器人)Automatedhandling.Computer-aidedprocessplanning(CAPP)AutoGrouptechnology(GT).matedandroboticassemblysystemsJust-in-timeproduction(JIT).Cellularmanufacturing(單元制造系統(tǒng)).Flexiblemanufacturingsystems(FMS)(柔性制造系統(tǒng)whatdoyouthinkabouttheconceptsofLeanProductionandAgileManufacturing?Leanproduction(精益生產(chǎn))，alsocalledleanmanufacturing,basicallyinvolved(a)amajorassessment(評估)ofeachactivityofcompanyregardingtheefficiencyandeffectivenessofitsoperations,(b)theefficiencyofthemachineryandequipmentusedintheoperationwhilemaintainingandimprovingquality,(c)thenumberofpersonnelinvolvedinaparticularoperation,and(d)athoroughanalysisinordertoreducethecostofeachactivity,includingbothproductiveandnonproductivelabor.Agileproduction(敏捷生產(chǎn))isatermcoinedtoindicatetheuseoftheprinciplesofleanproductiononabroaderscale.Theprinciplebehindagilemanufacturingisensuringflexibility(agility)inthemanufacturingenterprisesothatitcanquicklyrespondtochangesinproductvariety(產(chǎn)品品禾中)anddemandandcustomerneeds.PleasedefinetheProductintegrity,whichconceptsshouldbeincludedintheProductintegrity?Productintegrity(產(chǎn)品完整，性)isatermthatcanbedefinedbythedegreetowhichproduct(a)issuitableforitsintendedpurpose,(b)fillsarealmarketneed,(c)functionsreliablyduringitslifeexpectancy(在其壽命),and(d)canbemaintainedwithrelativeease.PleaseexplainthetermsofTotalqualitymanagement(TQM)andQualityassurance(QA).Totalqualitymanagement(TQM)andqualityassurancearetheresponsibilityofeveryoneinvolvedinthedesignandmanufactureofaproduct.TQMmeansthattheorganization'scultureisdefinedbyandsupportstheconstantattainmentofcustomersatisfactionthrougheranintegratedsystemoftools,techniques,andtraining.Thisinvolvesthecontinuousimprovementoforganizationalprocesses,resultinginhighqualityproductsandservices.QA:A11thoseplanedandsystematicactionsnecessarytoprovideadequateconfidencethataproduct(processplant)orservicewillsatisfyspecifiedrequirementsfirsttime.Qualityassurancenowincludestheimplementationofdesignofexperiments,atechniqueinwhichthefactorsinvolvedinaproductionprocessandtheirinteractionsarestudiedsimultaneously.Thus,variablesaffectingdimensionalaccuracyorsurfacefinishinamachiningoperationcanreadilybeidentified,allowingappropriateactionstobetaken.PleasediscussthegeneraltrendsinManufacturingfortodayindustrialfield(tryingtoANSWER:investigatethissubjectfromaspectsofmaterials,Processes,Equipment,andSystems)?Materials.Thetrendisforbettercontrolofmaterialscomposition,purity,anddefects(impurities,inclusions,flaws)inordertoenhancetheiroverallproperties,manufacturingcharacteristics,reliability,andservicelifewhilekeepingcostslow.Concernsoverenergyandmaterialsavingsareleadingtobetterrecyclability(回收)andhigherstrength-andstiffhess-to-weightratios.Developmentsarecontinuingonsuperconductors,semiconductors,nanomaterialsandnanopowders,amorphousalloys(非晶態(tài)合金)，shape-memoryalloys(smartmaterials)(形狀記'憶合金)，coatings,andvariousotherengineeredmetallicandnonmetallicmaterials.Processes,Equipment,andSystems.Continuingdevelopmentsincomputers,controls,industrialrobots,automatedinspection,handlingandassembly,andsensortechnology(傳感器技術(shù))arehavingamajorimpactontheefficiencyandreliability(效率和可靠，性)ofallmanufacturingprocessesandequipment.Advancesincomputerhardwareandsoftware,communicationssystems,adaptivecontrol,expertssystems,andartificialintelligenceandneuralnetworkshaveallhelpedenabletheeffectiveimplementationofconceptssuchasgrouptechnology,cellularmanufacturing,andflexiblemanufacturingsystems,aswellasmodempracticesintheefficientadministrationofmanufacturingorganizations.Computersimulationandmodelingarebecomingwidelyusedindesignandmanufacturing,resultingintheoptimizationofprocessesandproductionsystemsandbetterpredictionoftheeffectsofrelevantvariablesonproduct.CanyoucalculatethepercentelongationofmaterialsbaseonlyontheinformationgiveninFig.2.6?,IIeMe.￡=In—n—=en—=e-1Yes.kk(△/=/-")ExpIainifitispossibIeforthecurvesinFig.2.4toreach0%eIongationasthegageIengthisincreasedfurther.ThosecurveswiIInotapproachzeroeIongationbecausethespecimenhasaIreadyundergonesomefinitepermanenteIongationbeforefracture.ExpIainwhythedifferencebetweenengineeringstrainandtruestrainbecomesIargerasstrainincreases.IsthisphenomenontrueforbothtensiIeandcompressivestrains?ExpIain.Truestrain =I￡n—engineeringstraine= ForsmaIIvaIuesofengineeringstrain,=In(I+e)?e￡Yes.Intension-test,assumeI=kk=constant717Incompressive-test,assumeI=—.kForsmaIIvaIuesofengineeringstrain,thatiswhenkvaIueiscIoseto1,wecangetthat￡y=In—=In(I+ef)?，=—-1UsingthesamescaIeforstress,wenotethatthetensiIetruestress-truestraincurveishigherthantheengineeringstress-straincurve.ExpIainwhetherthisconditionaIsohoIdsforacompressiontestPPNo.engineeringstress(J=—truestress(J=—JJ&AIntension-test,thecrosssectionaIareaAisdecreasingasthespecimeniseIongated,itsvaIueissmaIIerthanAo.SothevaIueoftruestressisIargerthanthevaIueofengineeringstresswiththesamestrain,thatis,thetensiIetruestress-truestrainishigherthantheengineeringstress-straincurve.WhiIeincompression-test,thecrosssectionaIareaAisincreasingasspecimeniseIongated.SothevaIueoftruestressissmaIIerthanthevaIueofengineeringstresswiththesamestrain,thatis,thecompressivetruestress-truestrainisIowerthantheengineeringstress-straincurve.Whichofthetwotests,tensionorcompressionrequiresahigher-capacitytestingmachinethantheother?ExpIain.Compressiontestrequiresahigher-capacitytestingmachine.2.39WhenthespecimeniscompressedintothinsIice,whosethicknessisaImostzero,thetruestrainstendstoinfinity.2.40IngeneraI,materiaIcompressivestrengthishigherthantensiIestrength.SuchasbrittIemateriaIisveryeasytobreakintensiontest,butitcanbecompressedtoacertainIength.Explainhowthemodulusofresilienceofamaterialchanges,ifatall,asitisstrained:(1)foranelastic,perfectlyplasticmaterial,and(2)foranelastic,linearlystrain-hardeningmaterial.(1)Theelasticportionhasafiniteelasticmodulus,stressincreasesproportionallywithincreasingstrain.Oncethestressreachestheyieldstress,thestresskeepsthesamelevel.(2)Theelasticportionhasafiniteelasticmodulus,stressincreasesproportionallywithincreasingstrain.Oncethestressreachestheyieldstress,whiletheslopedecreaseswithincreasingstrain,thestressstillincreaseswithincreasingstain.Ifyoupullandbreakatension-testspecimenrapidly,wherewouldthetemperaturebethehighest?Explainwhy.Thetemperatureoftheneckingportionwillbethehighest.Strainiscausedbythedislocationandslip.Andtheformationandexpansionofdislocationareaprocessofreleasingenergy,inthisprocess,themechanicalenergyturnsintotheinternalenergy,thustheregion'stemperatureincreases.Thedensityofdislocationandthespeedofdislocation'sformationandexpansiondeterminethespeedofinternalenergygeneration.Inmetaltension-test,theneckingregion5sdensityofdislocationisthehighest,soitstemperatureshouldbethehighest.CommentonthetemperaturedistributionifthespecimeninQuestion2.7ispulledveryslowly.Internalenergydependsonitsgenerationspeedanddissipationspeed.Intension-test,ifthespecimenispulledslowly,theinternalenergyiscreatedslowly,atthesametime,heatdissipatesfastsincemetalisgoodconductorofheat.Inviewofthis,wecansaythetemperaturedistributionofthespecimenisalmostuniform.ThenoteatthebottomofTable2.5statesthatastemperatureincreases,Cdecreasesandmincreases.Explainwhy.Tensilestrengthbecomesmoreandmoresensitivetostrainrateastemperatureincreases,somincreasesastemperatureincreases.Andincreasingtemperatureprovidesmoreaccumulatedenergy,whichmakesmaterialspronetohaveplasticdeformation,sotheflowstressdecreasesastemperatureincreases.Andthereisequation:_c糜，socdecreaseswhilemincreasesand^decreases.YouaregiventheKandnvaluesoftwodifferentmaterials.Isthisinformationsufficienttodeterminewhichmaterialistougher?TOC\o"1-5"\h\z￡f 和N°, Toughness = - ￡s0 0￡fneed tobeknow.ModifythecurvesinFig.2.7toindicatetheeffectsoftemperature.Explainthereasonsforyourchanges.Increasingtemperatureprovidesmoreaccumulatedenergy,whichmakesmaterialspronetohaveplasticdeformation,soE=—ITheadhesiveforcebetweenatomsdecreasesastemperatureincreases,somodulusofeelasticitydecreases.Ypoint[YieldstrengthistheforceofdislocationovercomethepiningofaroundatomssuchasCottrellatmosphere.Whentemperatureincreases,theeffectofpiningthedislocationdiminishes,sothattheforcedislocationneededtoslipreduces,soyieldstrengthdeclines.UTSJMetalmaterialsaremadeofatoms,theatomicactivitiesaremoreintenseastemperatureincreases,anditsorganizationalstructureshowsinstability,sothematerialstrengthdeclines.ductilityf.Metalmaterialspronetohaveplasticdeformationastemperatureincreases,soductilityisimproved.據(jù)此畫圖Usingaspecificexample,showwhythedeformationrate,sayinm/s,andthetruestrainratearenotthesame./-Zo.Deformationratev= meansthelengthofelongationperunittime,soitsaysinm/s.Whilet??vithetruestrainrate變=jsoitshouldsayins.Ithasbeenstatedthatthehighervaluem,themorediffusetheneckis,andlikewise,thelowerthevalueofm,themorelocalizedtheneckis.Explainthereasonforthisbehavior.Whenneckingisabouttobegin,theregion'sstrengthwithrespecttotherestofthespecimenincreasesbecauseofstrainhardening.However,thestrainrateintheneckregionisalsohigherthanintherestofthespecimenbecausethematerialiselongatingfasterthere.Sincethematerialintheneckedregionisbecomingstrongerasitisstrainedatahigherrate,thisregionexhibitsahigherresistancetonecking.Becausetheresistancetoneckingincreasesasmincreases,soneckingbecomesmorediffusewithhighervalueofm.Explainwhymaterialswithhighmvalues,suchashotglassandsillyputty,whenstretchedslowly,undergolargeelongationsbeforefailure.Considereventstakingplaceintheneckedregionofthespecimen.Flowstressisknownasthestressrequiredtomaintainplasticdeformationatagivenstrain.Withhighmvalues,flowstressincreasesrapidlyasthestrainrateincreases.Whenthespecimenhasthetrendofnecking,thisregion'sstrainrateishigherthanintherestofthespecimenasthematerialiselongatingfasterthere,sothattheflowstressneededfordeformationincreasesrapidly,whichmakesdeformationcanonlyproceedinotherparts.Ifthespecimenhasthetrendofneckingagain,partofthespecimenishardenedbecauseofstrainrateincreasing,andneckingspreadtootherparts.Forthisreason,thespecimeneudergoeslargeelongation.Assumethatyouarerunningfour-pointbendingtestsonanumberofidenticalspecimensofthesamelengthandcrosssection,butwithincreasingdistancebetweentheupperpointsofloading.(SeeFig.2.21b)Whatchanges,ifany,wouldyouexpectinthetestresults?Explain.Itcanbeseenthatthemaximumbendingmomentdecreasewithincreasingdistancebetweentheupperpointswhileloadingofspecificload.WiththatSistaneeincreases,thespecimencanbearlargerload,sothestressatfractureinbendingtestincreases.WouldEq.(2.10)holdtrueintheelasticrange?No.Inelasticrange,withtheelongationofthespecimen,thevolumedoesnotremainconstant.Thatis,Do=L()*Ao,butD=L*A尹D().Whyhavedifferenttypesofhardnesstestsbeendeveloped?Howwouldyoumeasurethehardnessofaverylargeobject?Sincehardnessisnotafundamentalpropertybecauseresistancetoindentationdependsontheshapeoftheindenterandtheloadapplied,differenttestconditionsmayleaddifferentresults,andcertaintestmaynotmeetallmaterials.Sodifferenttypesofhardnesstestsaredeveloped.Iwillchoosethescleroscopetomeasurethehardness,becauseifsportableanditsscaleisenough.Whichhardnesstestsandscaleswouldyouuseforverythinstripsofmaterial,suchasaluminumfoil?Why?IwillchooseKnooptest.Whenmeasuringthehardnessofthinstrips,atoolargeloadcanmakethedepthcausedbytheloaddeeperthanthethicknessofspecimen.Ifthishappens,themeasuredhardnesswillbeacomprehensivehardnessofspecimenandsupportartifacts,andthemeasuredvalueisnotequaltothetruevalue.AndinKnooptest,theappliedloadistolighttoopenetratethespecimen.Listandexplainthefactorsthatyouwouldconsiderinselectinganappropriatehardnesstestandscaleforaparticularapplication.?Selecttheharnesstestaccordingtothemetalspecimen'sestimatedhardnesslevel,whichdependsonmateriaFscomposition,characteristicsandproductionprocess.?Selectthehardnesstestaccordingtospecimen'sthicknessandtreatmentprocess.③Selectthehardnesstestaccordingtospecimen'sdimension,numberandtestaccuracyrequirements.InaBrinellhardnesstest,theresultingimpressionisfoundtobeanellipse.Givepossibleexplanationsforthisphenomenon.Hardnessisnotafundamentalpropertybecauseresistancetoindentationdependsontheshapeoftheindenterandtheloadapplied.Besides,theindenterhasafiniteelasticmodulus,italsoundergoeselasticdeformationundertheappliedload,P.Thus,hardnessmeasurementsmaynotbeasaccurateasexpected,andtheloademployedshouldalsobecitedwiththetestresults,theBrinellhardnesstestissuitableforthematerialsoflowandmediumhardness.ReferringtoFig2.22,notethatthematerialforindentersareeithersteel,tungstencarbide,ordiamondusedforallofthetests?Thematerialforindentersareeithersteel,tungstencarbide,ordiamond,butnotusedforallofthetests.AstheFig2.22shows,steelandtungstencarbidearesuitablefortheBrinelltestand theRockwell(B/F/G/E)test,diamondpyramidissuitableforthevickersandknooptest,anddiamondconeissuitableforthetheRockwell(A/C/D)test.Whateffect,ifany,doesfrictionhaveinahardnesstest?Explain.Inahardnesstest,theeffectofthefrictiondependsonthesharperoftheindenterandthefrictioncoefficientofthematerials.ltwillhaveaneffecttotheimpression'sgeometry.Describethedifferencebetweencreeptandstress-relaxationphenomena,givingtwoexamplesforeachastheyrelatetoengineeringapplications.Creepisthepermanentelongation(永久伸長)ofamaterialunderastaticloadmaintainedforaperiodoftime.Itisaphenomenonofmetalsandsomenonmetallicmaterials,suchasthermoplasticsandrubbers,anditcanoccuratanytemperature.Stress-relaxationisthattheelasticdeformationisconvertedtothenonelasticdeformationforaperiodoftime whenthetotaldeformationisnotchanged,ithappensathightemperature.Thedifferencesarethattheformerisanaccumulationofnonelasticdeformationunderastaticload,andthelaterisanaccumulationofnonelasticdeformationwhenthetotaldeformationisnotchanged.Forexamples,theheattreatmentofthemetalwillhavecreep,thefastenersmayhaveastressrelaxationphenomeno.ReferringtothetwoimpacttestsshowninFig.2.29,explainhowdifferenttheresultswouldbeifthespecimenswereimpactedfromtheoppositedirection.Inthetwoimpacttests,wecanobtaintheenergydissipatedinbreakingthespecimenfromtheamountofswingofthependulum,thisenergyistheimpacttoughnessofthematerial.Besides,theyareusefulindeterminingtheductile-brittletransitiontemperatureofmaterials.Ifthespecimenswereimpactedfromtheoppositedirection,thisenergydissipatedmustbehigherthanthefdrmer.ltwilloverestimatetheimpacttoughnessofthematerialandtheductile-brittletransitiontemperatureofmaterials.IsitpossibletocompletelyremoveresidualstressinapieceofmaterialbythetechniquedescribedinFig.2.32ifthematerialiselasticJinearlystrainhardening?Explain.No.ThemechanismofresidualstressesreductionoreliminationbyplasticdeformationcanbedescribedinFig.2.32.Thismethodrequiressufficientstrainingtoestablishauniformlydistributedstresswithinthepart.Consequently,amaterialsuchastheelasticlinearlystrain-hardeningtypecanneverreachthisconditionsincethecompressivestresswillalwayslagbehindthetensilestress.ReferringtoFig.2.32,woulditbepossibletoeliminateresidualstressbycompressioninsteadoftension?Assumethatthepieceofmaterialwillnotbuckleundertheuniaxialcompressiveforce.No.Ifauniformlydistributedtensionisnowappliedtothispart,points Gcand01inthediagrammoveuponthestress-straincurve,asshownbythearrows.Themaximumlevelthatthesestresscanreachisthetensileyieldstress,Y.Unlikethatinthetensiontest,where,evenforveryductilemat