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时间:2019-07-04
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1、专业英语EnglishforSpecialPurposeLecturer:Mr.LüHongmingTel:0515-3127908Email:lhmyg@sina.com1.1概述第一篇专业英语基础第1章绪论1.课程教学目的培养学生对专业语言的理解能力和应用能力;让学生承担专业阅读必需的基本技能和知识,使学生能够以英语为工具获取专业科技知识及其他与专业有关的信息。2.专业英语的起源最初出现于20世纪50年代。3.专业英语的教学特点语言教学密切结合专业知识,教材大都来源于相关的专业文献。4.专业英语的学习方法专业英语阅读与普通英
2、语的快速阅读的方法也所不同,专业英语阅读要把准理解放在首位,在准确理解的基础上提高阅读速度。和其他的英语能力—祥,专业英语阅读能力,需要通过长期的实践才能获得,不可能一蹴而就,多读多练是提高专业英语阅读能力的最有效的方法。1.2专业英语的基本特点为了了解专业英语的特点,我们先阅读下面一段关于许用应力的课文。DespitethetestsdescribedinChapters1land12,materialsmaystillfailinservice,sometimeswithdisastrousresults(e.g.whent
3、hefailureoccursinaircraft.bridges,ships,etc.).Totrytoavoidsuchdisastrousoccurring,thedesigneravoidsusingmaterialscontinuouslyattheirmaximumallowablestress.Thisisdonebyemployingafactorofsafety.Unfortunately,increasingthestrengthofacomponentintheinterestsofsafetynotonl
4、yincreasestheinitialmaterialcosts,butalsotheoperatingcosts.Forexample,thestrongerandheavierthestructuremembersofanaircraft,thefewerpassengersitcancarryandthemorefuelitconsumers.Thereforeabalancehastobemaintainedbetweensafety,initialcostandoperatingcosts.Thedesigneris
5、constantlystrivingtoimprovetheformerwhilstreducingthelatter.Allowableworkingstressistakenasaproportionoftheyieldorproofstress;thatis,thecomponentisonlystressedwithinitselasticrangewheninservice.Forexample,considerthescrewedfasteningshowninFig.1.l.Whenthenutistightene
6、dnormallytheboltisstretchedslightlyand,providingitisstressedwithinitselasticrange,itwillbehavelikeaverypowerfulspringandwillpullthejointfacestogetherveryfirmly.Thestressintheboltismadeupoftwoelements.Firstly,thestressimpartedbytheinitialtighteningofthebolt;secondly,t
7、hestressimpartedbytheloadonthefasteninginservice.Thesumofthesestressmustnotbeallowedtoapproach,letaloneexceed,theyieldstressforthematerialofitwillceasetoactinanelasticmanner.Thereforethedesignerproportionsthefastening(anothercomponents)soasthatthereisafactorofsafety.
8、Usuallythedesignerassumesanallowableworkingstressofonlyhalftheyieldstressforthematerial.IfthefasteningshowninFig.1.1isoverstressedb
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