(1.3.5)-ch0-5 Chapter summary and review材料力学材料力学

Chapter0IntroductionChapterSummary&ReviewWelcometomechanicsofmaterials.Thisvideogiveschaptersummaryandreviewforthischapterintroduction.

Designcriteria-Strength-Stiffness-Stability-Dealswithreal,defromablematerials-StudieshowmaterialsbehaveunderloadingDistributionofinternalforcesexternalloadingsinternalreactionsdeformationmaterialfailurestressMechanicsofmaterials

*Inthischapter,welearnthatMechanicsofmaterialsdealswithreal,defromablematerials,Itstudieshowmaterialsbehaveunderloadingandhowmuchforceitcanwithstandwithoutbreaking,relatedtothreecriteria,strength,stiffnesandstability.Internalloadsanddeformation,stressandstrainaretheprimaryinterestsinmechancisofmaterials.seperateFBD

connectionforceoverallFBD

FCEDXDYBXBYEquilibriumequations:VectorformScalarform2D3DFree

BodyDiagramStaticsEquilibriumequationscanbeusedbothforevaluatingrigidbodiesordeformablebodies.Andequilibriumequationscanbeexpressedinvectorformorscalarform.Itisoftenmoreconvenienttousescalarform.Drawingfreebodydiagramsisthecornerstoneofallworkinthiscourse.Allforcesactingonthebodymustbedisplayedonthefree-bodydiagram,includingappliedforcesandmoments,reactionforcesandmoments,andanyconnectionforcesbetweenindividualcomponents.ExternalForcesForcesappliedtothestructurefromoutsideofthestructure.InternalForcesForcesproducedfromtheexternalforcesactingwithinastructure.FxFyFzMxMyMzFx

-Axialforce/normalforceMx

-TorqueFy,Fz

-ShearforceMy,Mz

-BendingmomentExternalforceisaforcethatactsfromtheoutsideofthestructure.Therearemanyexamplesofexternalforces,likegravitationalforce,friction,pullandpushforces,electromagneticforce,windforceandotherforces.Anexternalforceoccursasaresultofinteractionbetweenasystemandthesurroundings.Ontheotherhand,aninternalforceisaninteractionthatexistswithinasystem.Therefore,aninternalforceisaforcethatactswithinasystem.Externalforcescausemotioninanobject,whileaninternalforceresiststhemotion.Forinternalforces,therecanbeamaximumofsixindependantinternalreactioncomponents,threeinternalforcesandthreecouplemoments.Thesesixforcescanbeclassifiedintofourcategories,axialforceFX,transverseshearforcesFYandFZ,torsinalmomentMX,bendingmomentMYandMZ,correspondingtofourtypesofdeformationsMethodofsectionsq(x)P1P2①Cut：Makeanimaginarysectioncutnormaltotheaxisofamemberatthepointofinterest.q(x)P1P2q(x)VNM②FBD：Dawa

free-bodydiagramforeitherpart,includingalltheexternalforces,andinternalloads

onthecutsectionexertedbyanotherpart.③Equilibrium：Applyequilibriumequationstodetermineinternalloads.VNMP1P2Methodofsectionsisthestandardmethodtofindinternalloads.Whenapplyingthismethod,

firstlycutthememberintotwoparts.ThenselecteitherpartfromthetwoanddrawaFBDforit.Writedownquilibriumequationsforthispartandsolveforunknowninternalloads.Pleasenote,inmostcasesitispossibletowrite

oneequationtosolveforoneunknowndirectly.Solookforit

andtakeadvantageofsuchashortcut!

Stress

F

AM

Fx

Fz

FyNormalstressShearstressUnits:AveragenormalstressAverageshearstressNormalstressσ:producesachanginthelength

oftheelement.Shearstressτ:

producesachangeintheshapeoftheelement.Stressescanbeclasssifiedintonormalstressandshearstress.Normalstressesσproduceachanginthelength,Whiletheshearstressesτ

produceachangeintheshapeoftheelement.normalstressσandshearstessτcanbedefinedbytheseexpresions,thatisforcedividedbyarea.Andinmostcases,stressvarieswithlocationononecrosssection,bothmagnitudeanddirectionofstressesmayvary.Unitsofstressisnewtonspersquaremeter(N/m2),orpascal(Pa)intheSIunitssystem.Basicdeformationtypes②Shear①AxialtensionＦzy⑤Combindeddeformation③Tortion④BendingTransformationofabodyfromitsoriginalconfigurationtoanewconfiguration.DeformationDeformationistransformationofabodyfromitsoriginalconfigurationtoanewconfiguration,includingsizechangeandshapechange.Inthiscourse,deformationcanbeclassifiedintofourbasiccategories,*axialtension,*axialcompression,*shear,*torsion*and*bending.StrainNormalstrainε:sizechangeDimensionless＋:elongation－:contractionNormalstrainAveragenormalstrainΔsΔs’。

。。。nn’Shearstrainγ:

shapechange

Units:InradianChangeintherightanglentn’t’ShearstrainAsaforementioned,deformationincludessizechangeandshapechange.Sizechangeischaracterizedbynormalstrain,denotedbyε.Shapechangeischaracterizedbyshearstrain,denotedbyγ.normalstrainεequalstothelimitofnewlengthminusorignallengthdividedbyoriginallength,itisdimensionless.whileshearstrainγequalstothechangeofrightangle,itsunitsisradian