机械类外文文献Word格式.doc

机械类外文文献Word格式.doc

《机械类外文文献Word格式.doc》由会员分享，可在线阅读，更多相关《机械类外文文献Word格式.doc（10页珍藏版）》请在冰豆网上搜索。

外文原文：

FundamentalsofMechanicalDesign

Mechanicaldesignmeansthedesignofthingsandsystemsofamechanicalnature—machines,products,structures,devices,andinstruments.Forthemostpartmechanicaldesignutilizesmathematics,thematerialssciences,andtheengineering-mechanicssciences.

Thetotaldesignprocessisofinteresttous.Howdoesitbegin?

Doestheengineersimplysitdownathisdeskwithablanksheetofpaper?

And,ashejotsdownsomeideas,whathappensnext?

Whatfactorsinfluenceorcontrolthedecisionswhichhavetobemade?

Finally,then,howdoesthisdesignprocessend?

Sometimes,butnotalways,designbeginswhenanengineerrecognizesaneedanddecidestodosomethingaboutit.Recognitionoftheneedandphrasingitinsomanywordsoftenconstituteahighlycreativeactbecausetheneedmaybeonlyavaguediscontent,afeelingofuneasiness,ofasensingthatsomethingisnotright.

Theneedisusuallynotevidentatall.Forexample,theneedtodosomethingaboutafood-packagingmachinemaybeindicatedbythenoiselevel,bythevariationsinpackageweight,andbyslightbutperceptiblevariationsinthequalityofthepackagingorwrap.

Thereisadistinctdifferencebetweenthestatementoftheneedandtheidentificationoftheproblem.Whichfollowsthisstatement?

Theproblemismorespecific.Iftheneedisforcleanerair,theproblemmightbethatofreducingthedustdischargefrompower-plantstacks,orreducingthequantityofirritantsfromautomotiveexhausts.

Definitionoftheproblemmustincludeallthespecificationsforthethingthatistobedesigned.Thespecificationsaretheinputandoutputquantities,thecharacteristicsofthespacethethingmustoccupyandallthelimitationsonthesequantities.Wecanregardthethingtobedesignedassomethinginablackbox.Inthiscasewemustspecifytheinputsandoutputsoftheboxtogetherwiththeircharacteristicsandlimitations.Thespecificationsdefinethecost,thenumbertobemanufactured,theexpectedlife,therange,theoperatingtemperature,andthereliability.

Therearemanyimpliedspecificationswhichresulteitherfromthedesigner'

sparticularenvironmentorfromthenatureoftheproblemitself.Themanufacturingprocesseswhichareavailable,togetherwiththefacilitiesofacertainplant,constituterestrictionsonadesigner'

sfreedom,andhenceareapartoftheimpliedspecifications.Asmallplant,forinstance,maynotowncold-workingmachinery.Knowingthis,thedesignerselectsothermetal-processingmethodswhichcanbeperformedintheplant.Thelaborskillsavailableandthecompetitivesituationalsoconstituteimpliedspecifications.

Aftertheproblemhasbeendefinedandasetofwrittenandimpliedspecificationshasbeenobtained,thenextstepindesignisthesynthesisofanoptimumsolution.Nowsynthesiscannottakeplacewithoutbothanalysisandoptimizationbecausethesystemunderdesignmustbeanalyzedtodeterminewhethertheperformancecomplieswiththespecifications.

Thedesignisaniterativeprocessinwhichweproceedthroughseveralsteps,evaluatetheresults,andthenreturntoanearlierphaseoftheprocedure.Thuswemaysynthesizeseveralcomponentsofasystem,analyzeandoptimizethem,andreturntosynthesistoseewhateffectthishasontheremainingpartsofthesystem.Bothanalysisandoptimizationrequirethatweconstructordeviseabstractmodelsofthesystemwhichwilladmitsomeformofmathematicalanalysis.Wecallthesemodelsmathematicalmodels.Increatingthemitisourhopethatwecanfindonewhichwillsimulatetherealphysicalsystemverywell.

Evaluationisasignificantphaseofthetotaldesignprocess.Evaluationisthefinalproofofasuccessfuldesign,whichusuallyinvolvesthetestingofaprototypeinthelaboratory.Herewewishtodiscoverifthedesignreallysatisfiestheneedorneeds.Isitreliable?

Willitcompetesuccessfullywithsimilarproducts?

Isiteconomicaltomanufactureandtouse?

Isiteasilymaintainedandadjusted?

Canaprofitbemadefromitssaleoruse?

Communicatingthedesigntoothersisthefinal,vitalstepinthedesignprocess.Undoubtedlymanygreatdesigns,inventions,andcreativeworkshavebeenlosttomankindsimplybecausetheoriginatorswereunableorunwillingtoexplaintheiraccomplishmentstoothers.Presentationisasellingjob.Theengineer,whenpresentinganewsolutiontoadministrative,management,orsupervisorypersons,isattemptingtosellortoprovetothemthatthissolutionisabetterone.Unlessthiscanbedonesuccessfully,thetimeandeffortspentonobtainingthesolutionhavebeenlargelywasted.

Basically,thereareonlythreemeansofcommunicationavailabletous.Therearethewritten,theoral,andthegraphicalforms.Thereforethesuccessfulengineerwillbetechnicallycompetentandv