剪切與擠壓Shearandextrusion桿件的基本變形拉伸（壓縮）Stretch(compression)剪切與擠壓Shearandextrusion扭轉(zhuǎn)reverse彎曲bendBasicdeformationoftherod一、剪切shear二、擠壓Squeeze一、剪切shear一、剪切所謂聯(lián)接是指結(jié)構(gòu)或機(jī)械中用螺栓、銷(xiāo)釘、鍵、鉚釘和焊縫等將兩個(gè)或多個(gè)部件聯(lián)接而成。圖1銷(xiāo)軸連接圖2鉚釘連接shearTheso-calledconnectionreferstotheconnectionoftwoormorecomponentsinastructureormachineryusingbolts,pins,keys,rivets,andwelds.Figure1PinshaftconnectionFigure2RivetConnection一、剪切剪切變形是桿件的基礎(chǔ)變形之一，是指桿件受到一對(duì)垂直于桿軸的大小相等、方向相反、作用線相距很近的力作用后所引起的變形。桿件的剪切變形shearSheardeformationisoneofthebasicdeformationsofarod,whichreferstothedeformationcausedbyapairofforcesperpendiculartotherodaxisthatareofequalsize,oppositedirections,andcloselyspaced.Sheardeformationofmembers一、剪切受力特征：桿件受到兩個(gè)大小相等，方向相反、作用線垂直于桿的軸線并且相互平行且相距很近的力的作用。Forcecharacteristics:Therodissubjectedtotheactionoftwoforcesofequalsize,oppositedirection,perpendiculartotheaxisoftherod,paralleltoeachother,andcloselyspaced.變形特征：桿件沿兩力之間的截面發(fā)生錯(cuò)動(dòng)，直至破壞。Thememberundergoesdisplacementalongthecross-sectionbetweenthetwoforcesuntilitfails.剪切面shearplane剪切面shearplaneshear一、剪切實(shí)用計(jì)算：假設(shè)連接件剪切面上的應(yīng)力分布均等，從而算出截面上的平均剪應(yīng)力，或稱“名義剪應(yīng)力”。

剪切面shearPracticalcalculation:Assumingthatthestressdistributionontheshearplaneoftheconnectorisequal,theaverageshearstressonthesection,alsoknownasthe"nominalshearstress",canbecalculated.shearplane一、剪切實(shí)用計(jì)算：用與受剪構(gòu)件相同的材料制成試件，在試件與受剪構(gòu)件受力盡可能相似的條件下進(jìn)行直接剪切實(shí)驗(yàn)，用所得到的破壞荷載按照同樣的名義應(yīng)力公式算出材料的極限應(yīng)力τь

，將此極限應(yīng)力除以適當(dāng)?shù)陌踩禂?shù)即得到材料的許用剪切應(yīng)力[τ]。

剪切面shearplaneshearPracticalcalculation:Usingthesamematerialastheshearcomponenttomakespecimens,directshearexperimentsareconductedunderconditionswherethestressonthespecimensisassimilaraspossibletothatontheshearcomponent.Theultimatestressofthematerialiscalculatedusingthesamenominalstressformulabasedontheobtainedfailureloadτь，Dividethisultimatestressbyanappropriatesafetyfactortoobtaintheallowableshearstressofthematerial[τ]。一、剪切請(qǐng)計(jì)算下圖中銷(xiāo)軸的剪應(yīng)力。

FsF/2

shearPleasecalculatetheshearstressofthepinshaftinthefigurebelow.

二、擠壓Squeeze二、擠壓局部接觸面受壓的現(xiàn)象稱為擠壓，受壓的局部表面稱為擠壓面。剪切面shearplane擠壓面Extrusionsurface擠壓面ExtrusionsurfaceSqueezeThephenomenonoflocalcontactsurfacecompressioniscalledcompression,andthecompressedlocalsurfaceiscalledcompressionsurface.二、擠壓擠壓破壞的兩種形式Twoformsofcompressionfailure

鋼板在孔緣壓成橢圓Thesteelplateispressedintoanellipseattheholeedge

螺栓壓扁BoltflatteningSqueeze二、擠壓擠壓時(shí)兩接觸面上的壓力稱擠壓力，用Fs表示。其壓強(qiáng)稱為擠壓應(yīng)力，其方向垂直于擠壓面。在通常情況下，擠壓應(yīng)力只局限于接觸面的附近區(qū)域。

SqueezeThepressureonthetwocontactsurfacesduringextrusioniscalledtheextrusionforce,denotedbyFs.Itspressureiscalledcompressivestress,anditsdirectionisperpendiculartotheextrusionsurface.Undernormalcircumstances,compressivestressislimitedtotheareanearthecontactsurface.

二、擠壓實(shí)用計(jì)算：假設(shè)擠壓力Fs均勻地分布在擠壓面Ajy上

SqueezePracticalcalculation:AssumingthattheextrusionforceFsisuniformlydistributedontheextrusionsurfaceAjy

二、擠壓擠壓面積的面積Ajy計(jì)算CalculatetheareaAjyoftheextrusionarea當(dāng)擠壓面為平面接觸時(shí)，擠壓面積Ajy等于實(shí)際承壓面積Whentheextrusionsurfaceisinplanecontact,theextrusionareaAjyisequaltotheactualbearingarea當(dāng)接觸面為柱面時(shí)，擠壓面積Ajy為實(shí)際面積在其直徑平面上投影Whenthecontactsurfaceiscylindrical,theextrusionareaAjyistheactualareaprojectedonitsdiameterplaneSqueeze實(shí)際面積面Actualareasurface直徑投影面Diameterprojectionsurface二、擠壓通過(guò)實(shí)驗(yàn)來(lái)確定其半圓柱表面被壓潰的擠壓極限荷載，然后按照名義應(yīng)力公式算出其在直徑正投影面上的平均極限應(yīng)力，再除以適當(dāng)?shù)陌踩禂?shù)，就得到連接件材料的許用擠壓應(yīng)力[σjy]。

SqueezeDeterminethecompressiveultimateloadofitssemicylindricalsurfacebeingcrushedthroughexperiments,thencalculatetheaverageultimatestressonthediameterprojectionplaneaccordingtothenominalstressformula,anddivideitbyanappropriatesafetyfactortoobtaintheallowablecompressivestressoftheconnectingmaterial[σjy].

二、擠壓由于剪切和擠壓同時(shí)存在，為保證連接件的強(qiáng)度，材料的剪切強(qiáng)度條件和擠壓強(qiáng)度條件必須同時(shí)滿足：Duetothesimultaneousexistenceofshearandextrusion,inordertoensurethestrengthoftheconnector,theshearstrengthconditionandextrusionstrengthconditionofthematerialmustsimultaneouslymeet:

用剪切強(qiáng)度設(shè)計(jì)Designwithshearstrength用擠壓強(qiáng)度校核VerifywithextrusionstrengthSqueeze二、擠壓如圖傳動(dòng)軸，直徑d=50mm，齒輪與軸用平鍵聯(lián)接，傳遞的力偶矩Me=720N·m。鍵材料的許用切應(yīng)力[τ]=100MPa，許用擠壓應(yīng)力[σjy]=250MPa，試選擇平鍵，并校核強(qiáng)度。鍵key軸axle輪wheelSqueezeAsshowninthediagram,thetransmissionshafthasadiameterofd=50mm,andthegearisconnectedtotheshaftwithaflatkey.ThetransmittedtorqueisMe=720N·m.Allowableshearstressofkeymaterial[τ]=100MPa,allowableextrusionstress[σjy]=250MPa,tryselectingaflatkeyandverifythestrength.二、擠壓解：取軸鍵組合為研究對(duì)象進(jìn)行受力分析ΣM0=0F×d/2﹣Me=0F=2Me/d=28.8kN根據(jù)軸徑、傳遞的力偶矩查設(shè)計(jì)手冊(cè)，得到鍵的尺寸16*10*45（寬*高*長(zhǎng)）SqueezeSolution:TaketheshaftkeycombinationastheresearchobjectforforceanalysisAccordingtothedesignmanualbasedontheshaftdiameterandtransmittedtorque,thesizeofthekeyis16*10*45(width*height*length)二、擠壓鍵的強(qiáng)度校核——聯(lián)接鍵安全

按設(shè)計(jì)規(guī)范選取的鍵，能正常工作，通常不需再校核其強(qiáng)度SqueezeVerificationofKeyStrength-ConnectionKeySafetyThekeysselect