CHAPTER2SHEAR材料力学CHAPTER2SHEAR第二章剪切Productionoftheshearingstress剪切§2－1STRENGTHCALCULATIONABOUTSHEARANDBEARINGOFCONNECTINGMEMBERS§2－1连接件的剪切与挤压强度计算PP2)Characteristicsofloadsanddeformation：2、受力特点和变形特点：n剪切n剪切2、Practicalcalculationofshear剪切1)Shearingplane--AQ：Shiftingplane.Shearingforce--Q：Internalforceontheshearingplane.剪切3、Practicalcalculationsofbearing三、挤压的实用计算2)Bearingarea：AreaoftheprojectionplaneofthetouchingplaneinthedirectionperpendiculartoPjy2、挤压面积：接触面在垂直Pjy方向上的投影面的面积。4、Applications四、应用Example1Awoodentenonjointisshowninthefigure.Knowingthatthequantitiesarea=b=12cm，h=35cm，c=4.5cmandP=40KN.Trytodeterminetheshearingstressandbearingstressforthejoint.[例1]木榫接头如图所示，a=b=12cm，h=35cm，c=4.5cm,P=40KN，试求接头的剪应力和挤压应力。Solution：Freebodydiagramofthekeyisshowninthefigure解：键的受力分析如图Accordingtotheabovecalculation,strengthconditionsofthekeyaresatisfied.综上，键满足强度要求。Solution：Freebodydiagramofthekeyisshowninthefigure解：键的受力分析如图b剪切Solution：Freebodydiagramisshowninthefigure解：受力分析如图Thesections2—2and3—3ofthesteelplatearethecriticalsections.钢板的2--2和3--3面为危险面1、Internal-forceandaxial-forcediagramsoftherodintensionandcompression一、轴向拉压杆的内力及轴力图Simplemethodtodetermineaxialforces:①Taketheleftpartofthesectionxastheobject,theaxialforceonthesectionxcanbecalculatedbyfollowingformula:轴力的简便求法:①以x点左侧部分为研究对象,x点的轴力N(x)由下式计算:[Example1]Forces5P,8P,4PandPareactedatpointsA,B,CandDontherodrespectively，theirdirectionsareshowninthefigure.Trytoplottheaxial-forcediagramoftherod.[例1]图示杆的A、B、C、D点分别作用着5P、8P、4P、P的力，方向如图，试画出杆的轴力图。Positiveandnegativeofstress?应力的正负规定?3、Strengthdesigncriterion：三、强度设计准则（StrengthDesignCriterion）：1)Elasticlawoftherodwithequalaxialforces1、等轴力拉压杆的弹性定律4)Possion’sratio（orlateraldeformationfactor）4、泊松比（或横向变形系数）Assemblestress——initialstress装配应力——预应力5、Mechanicalpropertiesofthematerialsintensionandcompression五、材料在拉伸和压缩时的力学性能1)Practicalcalculationofshear1、剪切的实用计算Bearingarea剪切[Example2]TherodsAB、CD、EFandGHinthestructureareshowninthefigureEachofthemconsiststwoofrolledunequal-legssteels.Kn