力学专业英语Translation3

G1AxiallyLoadedBar轴向受载杆Thesimplestcasetoconsideratthestartisthatofaninitiallystraightmetalbarofconstantcrosssection,loadedatitsendsbyapairofoppositelydirectedcollinearforcescoincidingwiththelongitudinal(adj.经度的;纵向的;纵的;纵观的)axisofthebarandactingthroughthecentroid(n.质心；形心)ofeachcrosssection.（分句法）先考虑最简单的情况，一条起始横截面恒定的金属直棒，其两端受到一对反向共线力的作用。该对共线力的作用线与各截面形心组成的纵向轴线重合。Forstaticequilibriumthemagnitudesoftheforcesmustbeequal.（分句+直译）为了满足静力学平衡条件，力的大小必须相等。Iftheforcesaredirectedawayfromthebar,thebarissaidtobeintension;iftheyaredirectedtowardthebar,astateofcompressionexists.ThesetwoconditionsareillustratedinFig.1-1.（直译）如果这两个力的方向背离杆件，我们说杆件受拉；如果这两个力指向此杆，杆件受压。这两种情况如图1-1所示。Undertheactionofthispairofappliedforces,internalresistingforcesaresetupwithinthebarandtheircharacteristicsmaybestudiedbyimaginingaplanetobepassedthroughthebaranywherealongitslengthandoriented(导向）perpendicular（垂直的）tothelongitudinalaxisofthebar.Suchaplaneisdesignatedasa-ainFig.1-2(a).（分句法）在这一对应力的作用下，杆件内会形成内部抗力。并且，我们可以通过如下假想来研究它们的特性：一个平面在杆件的任意位置垂直于其长轴方向切入。该假想截面如图1-2(a)所示。Ifforpurposesofanalysistheportionofthebartotherightofthisplaneisconsideredtoberemoved,asinFig.1-2(b),thenitmustbereplacedbywhatevereffectitexertsupontheleftportion.Bythistechniqueofintroducingacuttingplane,theoriginallyinternalforcesnowbecomeexternalwithrespecttotheremainingportionofthebody.Forequilibriumoftheportiontotheleftthis“effect”mustbeahorizontalforceofmagnitudeP.However,thisforcePactingnormaltothecross-sectiona-aisactuallytheresultantofdistributedforcesactingoverthiscrosssectioninadirectionnormaltoit.（直译法）如果为了分析杆件的截面左边这部分，如图1-2(b)所示，可考虑将此截面右侧的杆件移除，那么它对左部分施加的效应必须被取代。通过引入截面的假想，原始的内力现在变成施加在右端的外力。为使左边这部分受力平衡，这种“效应”必须等于一个大小为P，向右的水平力。然而，这个垂直施加在截面a-a上的力P实际上是施加在整个截面上的法向分力的合力。Insteadofspeakingoftheinternalforceactingonsomesmallelementofarea,itisbetterforcomparative([kəm‘pærətɪv]比较的，相当的)purposestotreatthenormalforceactingoveraunitareaofthecrosssection(横截面).（状语前置）为了便于比较，与其讨论作用在杆件某处小面积上的内力，不如视法向力作用在横截面的单位面积上。Theintensityofnormalforceperunitareaistermedthenormalstressandisexpressedinunitsofforceperunitarea,e.g.1N/m2.（直译）单位面积上法向力的强度称为法向应力，（它的）单位用单位面积上的力的大小表示，如，1牛顿每平方米。Iftheforcesappliedtotheendsofthebararesuchthatthebarisintension,thentensilestresses([‘tɛnsl]张应力)aresetupinthebar;ifthebarisincompressionwehavecompressivestresses([kəm’prɛsɪv]压应力).（直译）如果作用在杆端的力使杆处于受拉状态，杆内就产生拉应力；如果杆处于受压状态，杆内就产生压应力。Itisessentialthatthelineofactionoftheappliedendforcespassthroughthecentroidofeachcrosssectionofthebar.（直译）作用在杆端的力的作用线必通过杆件每一截面的形心。TheaxialloadingshowninFig.1-2(a)occursfrequentlyinstructuralandmachinedesignproblems.如图1-2（a）所示的轴向荷载在建筑和机械设计中经常发生。Tosimulatethisloadinginthelaboratory,atestspecimenisheldinthegrips[ɡrɪp]ofeitheranelectricallydrivengear-typetestingmachineorahydraulic[haɪ'drɔlɪk]machine.为了在实验室模拟这种载荷，试件应夹持在电子或液压万能试验机的夹头中。Bothofthesemachinesarecommonlyusedinmaterialstestinglaboratoriesforapplyingaxialtension.这两种试验机通常在材料实验室用于施加轴向载荷。InanefforttostandardizematerialstestingtechniquestheAmericanSocietyforTestingMaterials(ASTM)hasissuedspecifications['spɛsəfə'keʃən]thatareincommonuse.为了使材料测试技术标准化，美国材料试验学会（ASTM）发布了通用规范。Onlytwoofthesewillbementionedhere,oneformetalplatesthickerthan3/16in(4.76mm)andappearingasinFig.1-3,theotherformetalsover1.5in(38mm)thickandhavingtheappearanceshowninFig.1-4.这里只提两种。一种如图1-3所示，其厚度超过3/16英寸（4.76mm）。另一种如图1-4所示，其直径粗于1.5英寸（38mm）。（1inch=25.4mm）Asmaybeseenfromthesefigures,thecentralportionofthespecimenissomewhatsmallerthantheendregionssothatfailurewillnottakeplaceinthegrippedportion.如图所示，试件的中部区域尺寸略小于两端尺寸，因此破坏不会发生在（试件）被夹持的两端。Theroundedfilletsshownareprovidedsothatnostressconcentrationswillariseatthetransitionbetweenthetwolateraldimensions.图示的圆角保证试件在两种尺寸的过渡部位不会发生应力集中。Thestandardgagelengthoverwhichelongationsaremeasuredis8in(203mm)forthespecimenshowninFig.1-3and2in(57mm)forthatshowninFig.1-4.（定语前置）供测量伸长量的标距长度为8英寸（203mm），如图1-3的试件所示；和2in（51mm)，如图1-4的试件所示。Theelongationsaremeasuredbyeithermechanicaloropticalextensometersorbycementinganelectricresistance-typestraingagetothesurfaceofthematerial.（定语前置）试件的伸长量既可以使用机械的、光学的伸长计，也可以用粘贴在试件表面的电阻应变片测量。Thisresistancestraingageconsistsofanumberofveryfinewiresorientedintheaxialdirectionofthebar.这种电阻应变片由许多个沿试件轴向的、很细的电阻丝组成。Asthebarelongates,theelectricalresistanceofthewireschangesandthischangeofresistanceisdetectedonaWheatstonebridgeandinterpretedaselongation.随着杆件伸长，电阻丝长度的变化引起电阻变化，这种电阻的变化由惠斯通电桥检测从而转换为伸长量。Letussupposethatoneofthesetensionspecimenshasbeenplacedinatension-compressiontestingmachineandtensileforcesgraduallyappliedtotheends.（让我们）假设这些拉伸试件之一已被置于拉伸-压缩试验机中，并且拉力逐渐施加到试件两端。Theelongationoverthegagelengthmaybemeasuredasindicatedaboveforanypredeterminedincrementsoftheaxialload.Fromthesevaluestheelongationperunitlength,whichistermednormalstrainanddenotedbyε,maybefoundbydividingthetotalelongationΔbythegagelengthL,thatis,ε=Δ/L.Thestrainisusuallyexpressedinunitsofinchesperinchormeterspermeterandconsequentlyisdimensionless.对于每一个预先指定的轴向载荷增量都要按上述方式测量相应的标距的伸长。由这些数值得到单位长度的伸长量，并将之定义为法向应变，用ε表示，可以用总伸长量Δ除以标距原长L得到法向应变的值。应变的单位通常是英寸每英寸或米每米，因此是无量纲。Astheaxialloadisgraduallyincreas