2008机制2材料力学试卷a答案

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1、厦门理工学院机械工程系2008机制材料力学试卷A一、（20）5.83Theworkingstressesforthemanufacturedwoodbeamare10MPainbendingand1.0MPainshear.Determinethelargestallowablevalueoftheloadintensityw0.Solution5(a)Designforshear8厦门理工学院机械工程系Themaximumshearforceisthefirstmomentofthecross-sectionalareaabovetheneutralaxisis3themomentofi

2、nertiaofthecross-sectionalabovetheneutralaxisis3--------P1634(b)DesignforbendingThenormalstress4Sothelargestallowablevalueoftheloadintensity1二、（20）TheoverhangingbeamABCcarriestheuniformlydistributedloadbetweenitssupportsandtheconcentratedloadPatendC.DeterminethedisplacementofthebeamattheC,bysuperp

3、osition.8厦门理工学院机械工程系5Accordingtodeflectionformulasforbeams,weknow，5，541三、（20）8.27Thecrosssectionsofthemembersofthepin-jointedstructureare200-mmsquare.FindthemaximumcompressivestressinmemberBDE.8厦门理工学院机械工程系15SolutionThemaximumcompressivestressinmemberBDE5四、（20）8.110Determinethesmallestallowablediam

4、eteroftheshaftthatcarriesthethreepulleys.Theworkingstressesareσw=18ksiandτw=8ksi.NeglecttheweightsofthePulleysandtheshaftaswellasthestressduetothetransverseshearforce.8厦门理工学院机械工程系SolutionAccordingthesupport,weknowthereisthelargestbendingmomentoccursatC,thelargesttorqueoccursinsegmentBC.Showinthefi

5、gure.，FBY=938.33(lb)，FDY=1511.67(lb)C点弯矩和扭矩：，D点弯矩和扭矩：，B点弯矩和扭矩：，7AtDsection,wehave8厦门理工学院机械工程系，Therefore,thestressatthebottomofthesectionare44DrawtheMohr’scircleAccordingtoMohr’scircle,wehaved=2.119(in.)4Settleit,wegetd=2.397(in.)五、（20）Forthetrussshowninthefigure(a),thecrosssectionofbarCDisshowinFi

6、g.(b),usingAISCcolumnspecificationswithE=200GPaandσyp=250MPa.,determinethemaximumsafevalueofP.Assumethatcross-bracingpreventsthejointsfromdeflectingperpendiculartotheplaneofthetruss.8厦门理工学院机械工程系SolutionDeterminetheforceFcxDeterminethemomentofinertiaofthecross-sectionalareaaboutthez-axisthemomentof

7、inertia8厦门理工学院机械工程系Area，Theslendernessratioofa1600mmx2400mmrectangleTheleastradiusofgyrationwithz-axis24Theslendernessratio4Fortheslendernessratioislessthan,sothattheconcretecolumnisofintermediatelength.Theseequa