《材料力學(xué)性能》大三教學(xué)PPT課件

《材料力學(xué)性能》大三教學(xué)PPT課件,材料力學(xué)性能,材料,力學(xué)性能,大三,教學(xué),PPT,課件 MechanicalTestsStaticTestsProperties:Elasticity,yield,plasticity,fracture,tughness,etc.Load:tension,compression,bending,torsion,etc.Coefficientofsoftnessofstressstate:=max/maxTensiontests:Engineeringstress/conditionalstress;Engineeringstrain/conditionalstrain.Engineeringstress/EngineeringstrainEngineeringstress/conditionalstress:Theinstantaneousloadappliedtoaspecimendividedbyitscross-sectionalareabeforeanydeformation.Engineeringstrain/conditionalstrain:Thechangeingaugelengthofaspecimen(inthedirectionofanappliedstress)dividedbyitsoriginalgaugelength.StandardtensilespecimenStress-strainbehaviorofelasticdeformationYieldingandyieldstrengthYielding:Theonsetofplasticdeformation.Yieldstrengthy:Thestressrequiredtoproduceaveryslightyetspecifiedamountofplasticstrain;astrainoffsetof0.002iscommonlyused.Proportionallimit:thepointonastress-straincurveatwhichthestraightlineproportionalitybetweenstressandstrainceases.TensilestrengthTensile(ultimate)strength(TS):Themaximumengineeringstress,intension,thatmaybesustainedwithoutfracture.DuctilityDuctilityAmeasureofamaterialsabilitytoundergoappreciableplasticdeformationbeforefracture;itmaybeexpressedaspercentelongation(%EL)orpercentreductioninarea(%RA)fromatensiletest.Stress-straincurvesofbrittleandductilematerialsEngineeringstress-strainbehaviorforironatthreetemperaturesTruestressandstrainTruestress:Theinstantaneousappliedloaddividedbytheinstantaneouscross-sectionalareaofaspecimen.Truestrain:Thenaturallogarithmoftheratioofinstantaneousgaugelengthtooriginalgaugelengthofaspecimenbeingdeformedbyauniaxialforce.IfnovolumechangeoccursduringdeformationOnlyvalidtotheonsetofneckingTypicaltensileengineeringstress-strainandtruestress-strainbehaviorsStrain-hardeningexponentFromtheonsetofplasticdeformationtothepointatwhichneckingbeginsElasticrecoveryduringplasticdeformationDefinitionsofandrelationshipsbetweentrueandengineeringstressandstrainStress-strainbehaviorofpolymersA-brittleB-plasticC-highlyelasticpolymersYieldandtensilestrengthsTheinfluenceoftemperatureonthestress-straincharacteristicsofpolymethylmethacrylateSchematictensilestress-straincurveforasemicrystallinepolymerproblemAcylindricalspecimenofsteelhavinganoriginaldiameterof12.8mmistensiletestedtofracturedandfoundtohaveanengineeringfracturestrengthof460MPa.Ifitscross-sectionaldiameteratfractureis10.7mm,determine:(a)Theductilityintermsofpercentreductioninarea.(b)ThetruestressatfractureGraphicaldeterminationofproportionallimitDeterminationoftheyieldlimitDeterminationofrelativeelongationProblemInthetensiletest,ifaspecimenrupturednearoneendinsteadofinthemiddleofthegaugelength,howtodetermineitsrelativeelongation?ProblemAcylindricalrodof380mmlonghavingadiameterof10.0mm,istobesubjectedtoatensileload.Iftheloadistoexperienceneitherplasticdeformationnoranelongationofmorethan0.9mmwhentheappliedloadis24500N,whichofthefourmetalsoralloysarepossiblecandidates?Justifyyourchoice(s).HardnesstestsHardness:Themeasureofamaterialsresistancetodeformationbysurfaceindentationorbyabrasion.Theeasiestandmostpopularmethodofmechanicaltestsofmaterials.Researchstudiesandcontrolmeansinindustry.Widelyusedinmanufacturingpracticefortheeaseandquicknessofmeasurement.Hardnesstestsareperformedmorefrequentlythananyothermechanicaltestforseveralreasons:Theyaresimpleandinexpensive;Thetestisnondestructive;Othermechanicalpropertiesoftenmaybeestimatedfromhardnessdata.ThereaumurhardnesstestAtthebeginningof18thcentury;TrihedralprismMohshardnessAtthebeginningof19thcentury;Ahardnessscaleforminerals,stillusedinmineralogy;Arranged10mineralsintoarowaccordingtotheirabilitytoscratchthesurfaceofotherminerals:10Diamond9Corundum8Topaz7Quartz6Orthoclase5Apatite4Fluorite3Calcite2Gypsum1TalcQuantitativehardnesstechniquesAsmallindenterisforcedintothesurfaceofamaterialtobetested,undercontrolledconditionsandofloadandrateofapplication.Thedepthorsizeofindentationismeasured,whichinturnisrelatedtoahardnessnumber.Rockwell,Brinell,KnoopandVickershardnesstests.HardnesstestingtechniquesRockwellhardnesstestsIndentersincludesphericalandhardenedsteelballshavingdiametersof1/16,1/8,1/4,andin.,andaconicaldiamondindenter,whichisusedforthehardestmaterials.RockwellhardnessscalesandSuperficialRockwellhardnessscales.HRA,HRB,HRCHR15N,HR30NRockwellhardnessscalesSuperficialRockwellhardnessscalesForeachscale,hardnessmayrangeupto130;however,ashardnessvaluesriseabove100ordropbellow20onanyscale,theybecameinaccurate.Inaccuraciesalsoresultifthetestspecimenistoothin,ifanindentationismadetoonearaspecimenedge,oriftwoindentationsaremadetooclosetooneanother.Specimenthicknessshouldbeatleasttentimestheindentationdepth,whereasallowanceshouldbemadeforatleastthreeindentationdiametersbetweenthecenteroneindentationandthespecimenedge,ortothecenterofasecondindentation.Furthermore,testingofspecimensstackedoneontopofanotherisnotrecommended.Also,accuracyisdependentontheindentationbeingmadeintoasmoothflatsurface.BrinellhardnesstestThediameterofthehardenedsteel(ortungstencarbide)indenteris10.00mm.Standardloadsrangebetween500and3000kgin500-kgincrements;Duringatest,theloadismaintainedconstantforaspecifiedtime(between10and30s).Minimumspecimenthicknessaswellasindentationposition(relativetospecimenedges)andminimumindentationspacingrequirementsarethesameasforRockwelltests.Inaddition,awell-definedindentationisrequired;thisnecessitatesasmoothflatsurfaceinwhichtheindentationismade.HBKnoopandVickersmicrohardnesstestsForeachtestaverysmalldiamondindenterhavingpyramidgeometryisforcedintothesurfaceofthespecimen.AppliedloadsaremuchsmallerthanforRockwellandBrinell,rangebetween1and1000g.Theresultingimpressionisobservedunderamicroscopeandmeasured;thismeasurementisthenconvertedintoahardnessnumber.Carefulspecimensurfacepreparation(grindingandpolishing)maybenecessarytoensureawell-definedindentationthatmaybeaccuratelymeasured.TheKnoopandVickersarehardnessnumbersaredesignatedbyHKandHV,respectively,andhardnessscalesforbothtechniquesareapproximatelyequivalent.KnoopandVickersarereferredtoasmicrohardnesstestingmethodsonthebasisofloadandindentersize.HardnessconversionCorrelationbetweenhardnessandtensilestrengthAsaruleofthumbformoststeels,theHBandthetensilestrengtharerelatedaccordingtoCompressivetestCompressionofcylindricaltestpiecesisoneofthesoftestmethod.Coefficientofsoftnessofstressstate:=max/max=2.Suitabletotestbrittlematerials.Testpiecepreparedforcompression1-lowersupport2-uppersphericalsupport3movablecross-pieceofthemachine4-testpieceCompressioncurvesConditionalandactualcompressiondiagramsofcopperDuctility(intensiletest)Ductilitypercentelongation(%EL)orpercentreductioninarea(%RA)fromatensiletest.Percentcontractionorpercentexpansioninareafromacompressivetest.TorsionalTestsFractureoftestpiecesintorsionTorsionaldiagramDetermineshearmodulusGValidintheelasticregion;M-thetorque,kgf.m;l0-thegaugelength,mm;-twistangleatthelengthl0,rad;d0-the cross-sectional diameter,mm.Determinethehighestrelativeshearmax=1-21and2aretheangularindicesattheendsofthegaugelength,rad;Conditional(engineering)strengthProportionallimitpr;Yieldlimit0.3;Conditionalultimatestrengthu.Actual(true)ultimatestrengthTestsofpieceswithstressconcentratorsStressconcentrationcoefficientacmaxisthemaximumaxialstress;isthenominaloraveragestressinthenotchsectioncisindependentofmaterialsproperties.StressdistributionofalargeplateStressdistributionfornotchedcylindricalsamples(elastic)Stressdistributionfornotchedcylindricalsamples(elastic-plastic)Fractograph(1)Fractograph(2)NotchSensitivityRatio(NSR)Bendingtests/Flexuralstrengtha-concentratedbendingb-purebendingMaximumstresses(a)(b)Three-pointbending,ASTMStandardc1161Flexuralstrength,bendingstrength,transverserupturestrengthForarectangularcrosssectionForacircularcrosssectionTypicalbendingdiagramsaplasticmaterialb-intermediatecasecbrittlematerialImpacttestingtechniquesCharpyimpacttestCharpyimpacttestImpacttoughness(k):k=mg(h-h)/A0Variablesincludingspecimensizeandshapeaswellasnotchconfigurationanddepthinfluencetheresults.TheCharpyv-notch(CVN)techniqueismostcommonlyused.Ductile-to-brittletransitionAppearanceofthefailuresurfaceisindicativeofthenatureoffracture,andmaybeusedintransitiontemperaturedeterminations.Forductilefracturethissurfaceappearsfibrousordull(orofshearcharacter);conversely,totalbrittlesurfacehaveagranular(shiny)texture(orcleavagecharacter).Overtheductile-to-brittletransition,featuresofbothtypeswillexist.NTD:NilDuctilitytemperature;50%FATT(FractureAppearanceTransitionTemperature):結(jié)晶區(qū)面積占整個(gè)斷面面積50%時(shí)的溫度叫做50%斷裂形貌(外觀）轉(zhuǎn)變溫度。DBTT:Ductile-to-BrittleTransitionTemperature.Notallmetalalloysdisplayaductile-to-brittletransition.FCCmetalsremainductileevenatextremelylowtemperatures.However,BCCandHCPalloysexperiencethistransition.Forthesematerialsthetransitiontemperatureissensitivetobothalloycompositionandmicrostructure.InfluenceofcarboncontentontheCVNenergy-versus-temperaturebehaviorforsteelProblem1st1.1 A cylindrical specimen of aluminumhavingadiameterof12.8mmandagaugelengthof50.80mmispulledintension.Usetheload-elongationcharacteristicstabulatedbellowtocompeteproblemsathroughe.(a)Plotthedataasengineeringstressversusengineeringstrain.(b)Computethemodulusofelasticity.(c)Determinetheyieldstrengthatastrainoffsetof0.002.(d)Determine the tensile strength of thisalloy.(e)What the approximate ductility,inpercentelongation?A0=128.6mm2E=179.5/0.00299MPa=60GPaTS=369MPa屈服強(qiáng)度277MPa%EL=(59.182-50.8)/50.8*100%=16.5%Problem2nd1.2Thefollowingtruestressesproducethecorrespondingtrueplasticstrainsforabrassalloy:Whattruestressisnecessarytoproduceatrueplasticstrainof0.25?1.2Strain-hardeningexponentK=630.957n=0.262=439MPaProblem3rd1.3 Consider a steel plate having a through-thicknessedgecracksimilartothatshownbellow;theplatewidth(W)is1000mm,anditsthicknessis 12mm.Furthermore,plane strain fracturetoughnessandyieldstrengthofthismaterialare80MPam1/2 and 1200MPa,If the plate is to beloadedtoastressof300MPa,wouldyouexpectfailuretooccuriftheonehalfcracklengthais15mm?Whyornot?Problem4th1.4TabulatedbellowaredatathatweregatheredfromaseriesofCharpyimpacttestsonaductilecastiron:(a)Plot the data as impact energy versustemperature.(b)Determinetheductile-to-brittletemperatureas that temperature corresponding to theaverageofthemaximumandminimumimpactenergies.(c)Determinetheductile-to-brittletemperatureasthattemperatureatwhichtheimpactenergyis80J.