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

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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
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