材料力学_孟广伟_chapter2

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1、FirstEditionCHAPTERMECHANICSOFMATERIALS2魏媛Tensionandcompression2006.10.1©2006.WeiYuan.Allrightsreserved.©2006.WeiYuan.Allrightsreserved.第二章轴向拉伸和压缩§2.1轴向拉伸和压缩的概念和实例CONCEPTANDEXAMPLE§2.2轴向拉伸和压缩时的内力和应力STRESSACTINGONTHESECTION§2.3材料在轴向拉伸和压缩时的力学性质MECHANICALPROPERTIESOFMATERIALSUNDERTENSII

2、ONANDCOMPRESSION§2.4许用应力、安全系数和强度条件PERMISSBLESTRESS,SAFETYFACTORANDSTRENGTHCONDITION©2006.WeiYuan.Allrightsreserved.§2.5轴向拉伸或压缩时的变形DEFORMATIONSUNDERTENSIONANDCOMPRESSION§2.6轴向拉伸或压缩时的弹性变形能STRAINENERGYUNDERTENSIONANDCOMPRESSION§2.7拉伸、压缩静不定问题STATICINDETERMINACYOFAXIALLOADEDMEMBERS§2.8应力集

3、中的概念STRESSCONCENTRATIONS©2006.WeiYuan.Allrightsreserved.§2.1轴向拉伸和压缩的概念和实例CONCEPTANDEXAMPLE一.实例EXAMPLE轴向拉伸轴向压缩AxialtensionAxialcompression©2006.WeiYuan.Allrightsreserved.二.外力Externalforces外力作用特点:Externalforcescharacteristic:力通过轴线Theforceisparalleltoaxes变形特点(主要):primarycharacteristicof

4、deformation:沿轴线方向伸长或缩短tensionorcompressionalongtheaxes受力简图：diagram：§2.2轴向拉伸和压缩时©2006.WeiYuan.Allrightsreserved.的内力和应力INTERNALFORCEANDSTRESSONTHESECTION一.横截面上的内力截面法：Methodofsection:Internalforceonthecross-section1.截２.取（任取）FIIIF３.代４.平FFNI∑F=0F=FxN1、F为内力,因过轴线,称轴力axialforceN说明2、轴力FN的符号规定

5、:拉为正、压为负Tensionispositiveandcompressionisnegative.©2006.WeiYuan.Allrightsreserved.轴力图Axialforcediagram当杆件受多个外力作用时，各段的内力将发生变化，为了明显地表现出轴力的大小、正负，引出内力图轴力图的画法取定坐标轴F（单位）N取定比例尺标出特征值x©2006.WeiYuan.Allrightsreserved.Example1Knowing:F=2.62kNF=1.3kN12F=1.32kN3PlottingaxialforcediagramSolution:1

6、.SoluteinternalforcesF112FFFN+F1=023112FN=−F1pressureF1F1FNN2F31F+F=0N23pressureF=−FN23F(kN)N2.Plotdiagramofinternalforce:1.322.62©2006.WeiYuan.Allrightsreserved.二.横截面上的应力StressonthecrosssectionFA1FFA1F11AA2F2FFF22A2>A1,F相同,哪个危险？A2>A1,F2>F1,哪个安全?A>A,equalF,whichdangerA>A,F>F,whichsaf

7、e212121©2006.WeiYuan.Allrightsreserved.公式推导Derivationoftheformulaaa′1.实验观察:直线平移Experiment:keepinglinearbb′2.推理:面平移judgment:keepingplaneaa′FF3.假设：平面假设ε=C1,σ=C2Assumption:planeassumptionbb′4.平衡方程:equilibriumequation:FσF=σdA=σdA=σAN∫∫AAFFNFNσ=A©2006.WeiYuan.Allrightsreserved.说明Illustrat

8、e1.外力作用线必须与杆