外文翻译--故障的分析、尺寸的决定以及凸轮的分析和应用.doc

附录附录1FAILUREANALYSIS，DIMENSIONALDETERMINATIONANDANALYSIS，APPLICATIONSOFCAMSINTRODUCTIONITISABSOLUTELYESSENTIALTHATADESIGNENGINEERKNOWHOWANDWHYPARTSFAILSOTHATRELIABLEMACHINESTHATREQUIREMINIMUMMAINTENANCECANBEDESIGNED．SOMETIMESAFAILURECANBESERIOUS，SUCHASWHENATIREBLOWSOUTONANAUTOMOBILETRAVELINGATHIGHSPEED．ONTHEOTHERHAND，AFAILUREMAYBENOMORETHANANUISANCE．ANEXAMPLEISTHELOOSENINGOFTHERADIATORHOSEINANAUTOMOBILECOOLINGSYSTEM．THECONSEQUENCEOFTHISLATTERFAILUREISUSUALLYTHELOSSOFSOMERADIATORCOOLANT，ACONDITIONTHATISREADILYDETECTEDANDCORRECTED．THETYPEOFLOADAPARTABSORBSISJUSTASSIGNIFICANTASTHEMAGNITUDE．GENERALLYSPEAKING，DYNAMICLOADSWITHDIRECTIONREVERSALSCAUSEGREATERDIFFICULTYTHANSTATICLOADS，ANDTHEREFORE，FATIGUESTRENGTHMUSTBECONSIDERED．ANOTHERCONCERNISWHETHERTHEMATERIALISDUCTILEORBRITTLE．FOREXAMPLE，BRITTLEMATERIALSARECONSIDEREDTOBEUNACCEPTABLEWHEREFATIGUEISINVOLVED．MANYPEOPLEMISTAKINGLYINTERPRETTHEWORDFAILURETOMEANTHEACTUALBREAKAGEOFAPART．HOWEVER，ADESIGNENGINEERMUSTCONSIDERABROADERUNDERSTANDINGOFWHATAPPRECIABLEDEFORMATIONOCCURS．ADUCTILEMATERIAL，HOWEVERWILLDEFORMALARGEAMOUNTPRIORTORUPTURE．EXCESSIVEDEFORMATION，WITHOUTFRACTURE，MAYCAUSEAMACHINETOFAILBECAUSETHEDEFORMEDPARTINTERFERESWITHAMOVINGSECONDPART．THEREFORE，APARTFAILSEVENIFITHASNOTPHYSICALLYBROKENWHENEVERITNOLONGERFULFILLSITSREQUIREDFUNCTION．SOMETIMESFAILUREMAYBEDUETOABNORMALFRICTIONORVIBRATIONBETWEENTWOMATINGPARTS．FAILUREALSOMAYBEDUETOAPHENOMENONCALLEDCREEP，WHICHISTHEPLASTICFLOWOFAMATERIALUNDERLOADATELEVATEDTEMPERATURES．INADDITION，THEACTUALSHAPEOFAPARTMAYBERESPONSIBLEFORFAILURE．FOREXAMPLE，STRESSCONCENTRATIONSDUETOSUDDENCHANGESINCONTOURMUSTBETAKENINTOACCOUNT．EVALUATIONOFSTRESSCONSIDERATIONSISESPECIALLYIMPORTANTWHENTHEREAREDYNAMICLOADSWITHDIRECTIONREVERSALSANDTHEMATERIALISNOTVERYDUCTILE．INGENERAL，THEDESIGNENGINEERMUSTCONSIDERALLPOSSIBLEMODESOFFAILURE，WHICHINCLUDETHEFOLLOWING．STRESSDEFORMATIONWEARCORROSIONVIBRATIONENVIRONMENTALDAMAGELOOSENINGOFFASTENINGDEVICESTHEPARTSIZESANDSHAPESSELECTEDALSOMUSTTAKEINTOACCOUNTMANYDIMENSIONALFACTORSTHATPRODUCEEXTERNALLOADEFFECTS，SUCHASGEOMETRICDISCONTINUITIES，RESIDUALSTRESSESDUETOFORMINGOFDESIREDCONTOURS，ANDTHEAPPLICATIONOFINTERFERENCEFITJOINTS．CAMSAREAMONGTHEMOSTVERSATILEMECHANISMSAVAILABLE．ACAMISASIMPLETWOMEMBERDEVICE．THEINPUTMEMBERISTHECAMITSELF，WHILETHEOUTPUTMEMBERISCALLEDTHEFOLLOWER．THROUGHTHEUSEOFCAMS，ASIMPLEINPUTMOTIONCANBEMODIFIEDINTOALMOSTANYCONCEIVABLEOUTPUTMOTIONTHATISDESIRED．SOMEOFTHECOMMONAPPLICATIONSOFCAMSARECAMSHAFTANDDISTRIBUTORSHAFTOFAUTOMOTIVEENGINEPRODUCTIONMACHINETOOLSAUTOMATICRECORDPLAYERSPRINTINGMACHINESAUTOMATICWASHINGMACHINESAUTOMATICDISHWASHERSTHECONTOUROFHIGHSPEEDCAMSCAMSPEEDINEXCESSOF1000RPMMUSTBEDETERMINEDMATHEMATICALLY．HOWEVER，THEVASTMAJORITYOFCAMSOPERATEATLOWSPEEDSLESSTHAN500RPMORMEDIUMSPEEDCAMSCANBEDETERMINEDGRAPHICALLYUSINGALARGESCALELAYOUT．INGENERAL，THEGREATERTHECAMSPEEDANDOUTPUTLOAD，THEGREATERMUSTBETHEPRECISIONWITHWHICHTHECAMCONTOURISMACHINED．DESIGNPROPERTIESOFMATERIALSTHEFOLLOWINGDESIGNPROPERTIESOFMATERIALSAREDEFINEDASTHEYRELATETOTHETENSILETEST．FIGURE27STATICSTRENGTH．THESTRENGTHOFAPARTISTHEMAXIMUMSTRESSTHATTHEPARTCANSUSTAINWITHOUTLOSINGITSABILITYTOPERFORMITSREQUIREDFUNCTION．THUSTHESTATICSTRENGTHMAYBECONSIDEREDTOBEAPPROXIMATELYEQUALTOTHEPROPORTIONALLIMIT，SINCENOPLASTICDEFORMATIONTAKESPLACEANDNODAMAGETHEORETICALLYISDONETOTHEMATERIAL．STIFFNESS．STIFFNESSISTHEDEFORMATIONRESISTINGPROPERTYOFAMATERIAL．THESLOPEOFTHEMODULUSLINEAND，HENCE，THEMODULUSOFELASTICITYAREMEASURESOFTHESTIFFNESSOFAMATERIAL．RESILIENCE．RESILIENCEISTHEPROPERTYOFAMATERIALTHATPERMITSITTOABSORBENERGYWITHOUTPERMANENTDEFORMATION．THEAMOUNTOFENERGYABSORBEDISREPRESENTEDBYTHEAREAUNDERNEATHTHESTRESSSTRAINDIAGRAMWITHINTHEELASTICREGION．TOUGHNESS．RESILIENCEANDTOUGHNESSARESIMILARPROPERTIES．HOWEVER，TOUGHNESSISTHEABILITYTOABSORBENERGYWITHOUTRUPTURE．THUSTOUGHNESSISREPRESENTEDBYTHETOTALAREAUNDERNEATHTHESTRESSSTRAINDIAGRAM，ASDEPICTEDINFIGURE2．8B．OBVIOUSLY，THETOUGHNESSANDRESILIENCEOFBRITTLEMATERIALSAREVERYLOWANDAREAPPROXIMATELYEQUAL．BRITTLENESS．ABRITTLEMATERIALISONETHATRUPTURESBEFOREANYAPPRECIABLEPLASTICDEFORMATIONTAKESPLACE．BRITTLEMATERIALSAREGENERALLYCONSIDEREDUNDESIRABLEFORMACHINECOMPONENTSBECAUSETHEYAREUNABLETOYIELDLOCALLYATLOCATIONSOFHIGHSTRESSBECAUSEOFGEOMETRICSTRESSRAISERSSUCHASSHOULDERS，HOLES，NOTCHES，ORKEYWAYS．DUCTILITY．ADUCTILITYMATERIALEXHIBITSALARGEAMOUNTOFPLASTICDEFORMATIONPRIORTORUPTURE．DUCTILITYISMEASUREDBYTHEPERCENTOFAREAANDPERCENTELONGATIONOFAPARTLOADEDTORUPTURE．A5ELONGATIONATRUPTUREISCONSIDEREDTOBETHEDIVIDINGLINEBETWEENDUCTILEANDBRITTLEMATERIALS．MALLEABILITY．MALLEABILITYISESSENTIALLYAMEASUREOFTHECOMPRESSIVEDUCTILITYOFAMATERIALAND，ASSUCH，ISANIMPORTANTCHARACTERISTICOFMETALSTHATARETOBEROLLEDINTOSHEETS．FIGURE28HARDNESS．THEHARDNESSOFAMATERIALISITSABILITYTORESISTINDENTATIONORSCRATCHING．GENERALLYSPEAKING，THEHARDERAMATERIAL，THEMOREBRITTLEITISAND，HENCE，THELESSRESILIENT．ALSO，THEULTIMATESTRENGTHOFAMATERIALISROUGHLYPROPORTIONALTOITSHARDNESS．MACHINABILITY．MACHINABILITYISAMEASUREOFTHERELATIVEEASEWITHWHICHAMATERIALCANBEMACHINED．INGENERAL，THEHARDERTHEMATERIAL，THEMOREDIFFICULTITISTOMACHINE．COMPRESSIONANDSHEARSTATICSTRENGTHINADDITIONTOTHETENSILETESTS，THEREAREOTHERTYPESOFSTATICLOADTESTINGTHATPROVIDEVALUABLEINFORMATION．COMPRESSIONTESTING．MOSTDUCTILEMATERIALSHAVEAPPROXIMATELYTHESAMEPROPERTIESINCOMPRESSIONASINTENSION．THEULTIMATESTRENGTH，HOWEVER，CANNOTBEEVALUATEDFORCOMPRESSION．ASADUCTILESPECIMENFLOWSPLASTICALLYINCOMPRESSION，THEMATERIALBULGESOUT，BUTTHEREISNOPHYSICALRUPTUREASISTHECASEINTENSION．THEREFORE，ADUCTILEMATERIALFAILSINCOMPRESSIONASARESULTOFDEFORMATION，NOTSTRESS．SHEARTESTING．SHAFTS，BOLTS，RIVETS，ANDWELDSARELOCATEDINSUCHAWAYTHATSHEARSTRESSESAREPRODUCED．APLOTOFTHETENSILETEST．THEULTIMATESHEARINGSTRENGTHISDEFINEDASTHESTRESSATWHICHFAILUREOCCURS．THEULTIMATESTRENGTHINSHEAR，HOWEVER，DOESNOTEQUALTHEULTIMATESTRENGTHINTENSION．FOREXAMPLE，INTHECASEOFSTEEL，THEULTIMATESHEARSTRENGTHISAPPROXIMATELY75OFTHEULTIMATESTRENGTHINTENSION．THISDIFFERENCEMUSTBETAKENINTOACCOUNTWHENSHEARSTRESSESAREENCOUNTEREDINMACHINECOMPONENTS．DYNAMICLOADSANAPPLIEDFORCETHATDOESNOTVARYINANYMANNERISCALLEDASTATICORSTEADYLOAD．ITISALSOCOMMONPRACTICETOCONSIDERAPPLIEDFORCESTHATSELDOMVARYTOBESTATICLOADS．THEFORCETHATISGRADUALLYAPPLIEDDURINGATENSILETESTISTHEREFOREASTATICLOAD．ONTHEOTHERHAND，FORCESTHATVARYFREQUENTLYINMAGNITUDEANDDIRECTIONARECALLEDDYNAMICLOADS．DYNAMICLOADSCANBESUBDIVIDEDTOTHEFOLLOWINGTHREECATEGORIES．VARYINGLOAD．WITHVARYINGLOADS，THEMAGNITUDECHANGES，BUTTHE