1、附录附录1FailureAnalysis，DimensionalDeterminationAndAnalysis，ApplicationsOfCamsINTRODUCTIONItisabsolutelyessentialthatadesignengineerknowhowandwhypartsfailsothatreliablemachinesthatrequireminimummaintenancecanbedesignedSometimesafailurecanbeserious，suchaswhenatireblowsoutonanautomobiletravelingathighspe
2、edOntheotherhand，afailuremaybenomorethananuisanceAnexampleisthelooseningoftheradiatorhoseinanautomobilecoolingsystemTheconsequenceofthislatterfailureisusuallythelossofsomeradiatorcoolant，aconditionthatisreadilydetectedandcorrectedThetypeofloadapartabsorbsisjustassignificantasthemagnitudeGenerallyspe
3、aking，dynamicloadswithdirectionreversalscausegreaterdifficultythanstaticloads，andtherefore，fatiguestrengthmustbeconsideredAnotherconcerniswhetherthematerialisductileorbrittleForexample，brittlematerialsareconsideredtobeunacceptablewherefatigueisinvolvedManypeoplemistakinglyinterpretthewordfailuretome
4、antheactualbreakageofapartHowever，adesignengineermustconsiderabroaderunderstandingofwhatappreciabledeformationoccursAductilematerial，howeverwilldeformalargeamountpriortoruptureExcessivedeformation，withoutfracture，maycauseamachinetofailbecausethedeformedpartinterfereswithamovingsecondpartTherefore，ap
5、artfails(evenifithasnotphysicallybroken)wheneveritnolongerfulfillsitsrequiredfunctionSometimesfailuremaybeduetoabnormalfrictionorvibrationbetweentwomatingpartsFailurealsomaybeduetoaphenomenoncalledcreep，whichistheplasticflowofamaterialunderloadatelevatedtemperaturesInaddition，theactualshapeofapartma
6、yberesponsibleforfailureForexample，stressconcentrationsduetosuddenchangesincontourmustbetakenintoaccountEvaluationofstressconsiderationsisespeciallyimportantwhentherearedynamicloadswithdirectionreversalsandthematerialisnotveryductileIngeneral，thedesignengineermustconsiderallpossiblemodesoffailure，wh
7、ichincludethefollowingStressDeformationWearCorrosionVibrationEnvironmentaldamageLooseningoffasteningdevicesThepartsizesandshapesselectedalsomusttakeintoaccountmanydimensionalfactorsthatproduceexternalloadeffects，suchasgeometricdiscontinuities，residualstressesduetoformingofdesiredcontours，andtheappli
8、cationofinterferencefitjointsCamsareamongthemostversatilemechanismsavailableAcamisasimpletwo-memberdeviceTheinputmemberisthecamitself，whiletheoutputmemberiscalledthefollowerThroughtheuseofcams，asimpleinputmotioncanbemodifiedintoalmostanyconceivableoutputmotionthatisdesiredSomeofthecommonapplications
9、ofcamsareCamshaftanddistributorshaftofautomotiveengineProductionmachinetoolsAutomaticrecordplayersPrintingmachinesAutomaticwashingmachinesAutomaticdishwashersThecontourofhigh-speedcams(camspeedinexcessof1000rpm)mustbedeterminedmathematicallyHowever，thevastmajorityofcamsoperateatlowspeeds(lessthan500
10、rpm)ormedium-speedcamscanbedeterminedgraphicallyusingalarge-scalelayoutIngeneral，thegreaterthecamspeedandoutputload，thegreatermustbetheprecisionwithwhichthecamcontourismachinedDESIGNPROPERTIESOFMATERIALSThefollowingdesignpropertiesofmaterialsaredefinedastheyrelatetothetensiletestFigure2/7StaticStren
11、gthThestrengthofapartisthemaximumstressthatthepartcansustainwithoutlosingitsabilitytoperformitsrequiredfunctionThusthestaticstrengthmaybeconsideredtobeapproximatelyequaltotheproportionallimit，sincenoplasticdeformationtakesplaceandnodamagetheoreticallyisdonetothematerialStiffnessStiffnessisthedeforma
12、tion-resistingpropertyofamaterialTheslopeofthemoduluslineand，hence，themodulusofelasticityaremeasuresofthestiffnessofamaterialResilienceResilienceisthepropertyofamaterialthatpermitsittoabsorbenergywithoutpermanentdeformationTheamountofenergyabsorbedisrepresentedbytheareaunderneaththestress-straindiag
13、ramwithintheelasticregionToughnessResilienceandtoughnessaresimilarpropertiesHowever，toughnessistheabilitytoabsorbenergywithoutruptureThustoughnessisrepresentedbythetotalareaunderneaththestress-straindiagram，asdepictedinFigure28bObviously，thetoughnessandresilienceofbrittlematerialsareverylowandareapp
14、roximatelyequalBrittlenessAbrittlematerialisonethatrupturesbeforeanyappreciableplasticdeformationtakesplaceBrittlematerialsaregenerallyconsideredundesirableformachinecomponentsbecausetheyareunabletoyieldlocallyatlocationsofhighstressbecauseofgeometricstressraiserssuchasshoulders，holes，notches，orkeyw
15、aysDuctilityAductilitymaterialexhibitsalargeamountofplasticdeformationpriortoruptureDuctilityismeasuredbythepercentofareaandpercentelongationofapartloadedtoruptureA5%elongationatruptureisconsideredtobethedividinglinebetweenductileandbrittlematerialsMalleabilityMalleabilityisessentiallyameasureofthec
16、ompressiveductilityofamaterialand，assuch，isanimportantcharacteristicofmetalsthataretoberolledintosheetsFigure2/8HardnessThehardnessofamaterialisitsabilitytoresistindentationorscratchingGenerallyspeaking，theharderamaterial，themorebrittleitisand，hence，thelessresilientAlso，theultimatestrengthofamateria
17、lisroughlyproportionaltoitshardnessMachinabilityMachinabilityisameasureoftherelativeeasewithwhichamaterialcanbemachinedIngeneral，theharderthematerial，themoredifficultitistomachineCOMPRESSIONANDSHEARSTATICSTRENGTHInadditiontothetensiletests，thereareothertypesofstaticloadtestingthatprovidevaluableinfo
18、rmationCompressionTestingMostductilematerialshaveapproximatelythesamepropertiesincompressionasintensionTheultimatestrength，however，cannotbeevaluatedforcompressionAsaductilespecimenflowsplasticallyincompression，thematerialbulgesout，butthereisnophysicalruptureasisthecaseintensionTherefore，aductilemate
19、rialfailsincompressionasaresultofdeformation，notstressShearTestingShafts，bolts，rivets，andweldsarelocatedinsuchawaythatshearstressesareproducedAplotofthetensiletestTheultimateshearingstrengthisdefinedasthestressatwhichfailureoccursTheultimatestrengthinshear，however，doesnotequaltheultimatestrengthinte
20、nsionForexample，inthecaseofsteel，theultimateshearstrengthisapproximately75%oftheultimatestrengthintensionThisdifferencemustbetakenintoaccountwhenshearstressesareencounteredinmachinecomponentsDYNAMICLOADSAnappliedforcethatdoesnotvaryinanymanneriscalledastaticorsteadyloadItisalsocommonpracticetoconsid
21、erappliedforcesthatseldomvarytobestaticloadsTheforcethatisgraduallyappliedduringatensiletestisthereforeastaticloadOntheotherhand，forcesthatvaryfrequentlyinmagnitudeanddirectionarecalleddynamicloadsDynamicloadscanbesubdividedtothefollowingthreecategoriesVaryingLoadWithvaryingloads，themagnitudechanges，butthe
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