机械专业毕业设计---外文翻译

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1、FailureAnalysis,DimensionalDeterminationAndAnalysis,ApplicationsOfCamsINTRODUCTIONItisabsolutelyessentialthatadesignengineerknowhowandwhypartsfailsothatreliablemachinesthatrequireminimummaintenancecanbedesigned-Sometimesafailurecanbeserious,suchaswhenatireblowsoutonanautomobiletravelingath

2、ighspeed.Ontheotherhand,afailuremaybenomorethananuisance.Anexampleisthelooseningoftheradiatorhoseinanautomobilecoolingsystem.Theconsequenceofthislatterfailureisusuallythelossofsomeradiatorcoolant,aconditionthatisreadilydetectedandcorrected.Thetypeofloadapartabsorbsisjustassignificantasthem

3、agnitude.Generallyspeaking,dynamicloadswithdirectionreversalscausegreaterdifficultythanstaticloads,andtherefore,fatiguestrengthmustbeconsidered.Anotherconcerniswhetherthematerialisductileorbrittle.Forexample,brittlematerialsareconsideredtobeunacceptablewherefatigueisinvolved.Manypeoplemist

4、akinglyinterpretthewordfailuretomeantheactualbreakageofapart.However,adesignengineermustconsiderabroaderunderstandingofwhatappreciabledeformationoccurs.Aductilematerial,howeverwilldeformalargeamountpriortorupture.Excessivedeformation,withoutfracture,maycauseamachinetofailbecausethedeformed

5、partinterfereswithamovingsecondpart.Therefore,apartfails(evenifithasnotphysicallybroken)wheneveritnolongerfulfillsitsrequiredfunction.Sometimesfailuremaybeduetoabnormalfrictionorvibrationbetweentwomatingparts.Failurealsomaybeduetoaphenomenoncalledcreep,whichistheplasticflowofamaterialunder

6、loadatelevatedtemperatures.Inaddition,theactualshapeofapartmayberesponsibleforfailure.Forexample,stressconcentrationsduetosuddenchangesincontourmustbetakenintoaccount.Evaluationofstressconsiderationsisespeciallyimportantwhentherearedynamicloadswithdirectionreversalsandthematerialisnotveryd

7、uctile.Ingeneralthedesignengineermustconsiderallpossiblemodesoffailurewhichincludethefollowing.StressDeformationWearCorrosionVibrationEnvironmentaldamageLooseningoffasteningdevicesThepartsizesandshapesselectedalsomusttakeintoaccountmanydimensionalfactorsthatpr