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1、1课Thatbranchofscientificanalysiswhichmotions,timesandforcesiscalledmechanicsandismadeupoftwoparts,staticsanddynamics.研究位移、时间和力是科学分析法的一个分支,被称作力学,力学由两大部分组成,静力学和动力学。Forexample,iftheforceoperatingonasleevebearingbecomestoohigh,itwillsqueezeouttheoilfilmandcausemetal-to-metalconta
2、ct,overheatingandrapidfailureofthebearing.例如:如果止推轴承上的作用力过大的话,会挤出油膜,引起金属和金属之间的相互接触,轴承将过热而迅速失效。Ourintuitiveconceptofforceincludessuchideasasplaceofapplication,direction,andmagnitude,andthesearecalledthecharacteristicsofaforce.力的直观概念包括力的作用点、大小、方向,这些被称为力的三要素。Allbodiesareeitherela
3、sticorplasticandwillbedeformedifacteduponbyforces.Whenthedeformationofsuchbodiesissmall,theyarefrequentlyassumedtoberigid,i.e.,incapableofdeformation,inordertosimplifytheanalysis.所有的物体既可以是弹性的也可以是塑性的,如果受到力的作用就产生变形。当变形很小的时候它们被假设成刚体,也就是不产生变形。Therigid-bodyassumptioncannotbeusedin
4、internalstressesandstrainsduetotheappliedforcestobeanalyzed.Thusweconsiderthebodytobecapableofdeforming.刚体假设不能应用于内应力和内应变的分析,所以在实际力的分析时,要考虑物体的形变。Ifalltheforcesactingonaparticlearebalanced,theparticlewilleitherremainatrestorwillcontinuetomoveinastraightlineatauniformvelocity.如果
5、作用在质点上所有的力是平衡的,质点将会保持静止或做做匀速直线运动。3课Virtuallyallmachinescontainshafts.Themostcommonshapeforshaftsiscircularandthecrosssectioncanbeeithersolidorhollow(hollowshaftscanresultinweightsavings).几乎所有的机器都有轴,最常用的外形是圆形的,横截面是空心的或实心的圆形截面(空心轴可以减少重量)。Ashaftmusthaveadequatetorsionalstrengtht
6、otransmittorqueandnotbeoverstressed.Itmustalsobetorsionallystillenoughsothatonemountedcomponentdoesnotdeviateexcessivelyfromitsoriginalangularpositionrelativetoasecondcomponentmountedonthesameshaft.一个轴必须有足够的扭转强度来传递扭矩而不会破坏,同样也必须有足够的扭转刚度,这样安装轴就不能过度偏离相对于安装在同一轴上第二个零件的原始位置。Shaftsa
7、remountedonbearingsandtransmitpowerthroughsuchdevicesasgears,pulleys,camsandclutches.Thesedevicesintroduceforceswhichattempttobendtheshaft;hence,theshaftmustberigidenoughtopreventoverloadingofthesupportingbearings.轴安装在轴承上通过齿轮,滑轮,凸轮和离合器这些装置传递力。这些装置可以产生使轴弯曲的力,所以轴必修有足够的刚性防止支撑轴承的
8、过载。Inaddition,theshaftmustbeabletosustainacombinationofbendingandtor