无机非金属材料工程专业英语 第6章

Chapter6Mechanicalproperties,Whystudymechanicalproperties?,Asamaterialengineers,itisincumbent(obligatory有义务的)tounderstandhowthevariousmechanicalpropertiesaremeasuredandwhatthesepropertiesrepresent.Incasethatyouarecalledupon(ordered;required)todesignstructuresorcomponentsusingpredeterminedmaterialssuchthatunacceptablelevelsofdeformationorfailurewillnotoccur,theadequateknowledgeonmechanicalpropertiesofthematerialisamatteroflife.,Whatshouldyoubeabletodoafterstudyingthischapter?,knowwhatatensile-testingapparatusisusedfor.Knowhowstress-straincurveisobtained.Namewhatarethemainmechanicalproperties。,Importanttermsandconcepts:,Anelasticityn.滞弹性stressn.应力ductilityn.延展性，塑性elasticadj.弹性的truestress真应力engineeringstress工程应力,Elasticityn.弹性strainn.应变brittlementn.脆性plasticadj.塑性的truestrain真应变engineeringstrain工程应变,Stress-straincurve应力应变曲线,elasticrecovery弹性回复stiffnessn.刚度modulusofelasticity弹性模量deformv.distort/bend/twist：Toaltertheshapeofbypressureorstress.使变形：通过压力或拉力改变的形状Deformationn.变形,yieldingadj.Inclinedtogivewaytopressure,orinfluence.屈服的。yieldstrength屈服强度tensilestrength拉伸强度elongationtofracture延伸率Poissonsratio泊松比proportionallimit比例极限resilience:Thepropertyofamaterialthatenablesittoresumeitsoriginalshapeorpositionafterbeingbent,stretched,orcompressed;elasticity.弹性：使某物质能在弯曲、伸展或收缩后恢复原先的形状或位置的物体的性能；收缩性.,safestress安全应力shear剪切toughness韧性fracturetoughness断裂韧度impacttoughness冲击韧性hardnessn.硬度Rochwellhardness洛氏硬度Brinellhardness布氏硬度Knoophardness努氏硬度Vichershardness维氏硬度Indenter压头Hookeslaw虎克定律,ascertained:adj.determinedreplicatevt.duplicate,copy,reproduce,orrepeat.复制：复印、复写、复制或重复fluctuatevt.varyirregularly,swing波动,变动imperative-urgentProfessionalsociety专业协会ASTM-AmericanSocietyforTestingandMaterialsConfinevt.restrict/limit,Fourstress-straintesttypes:Tension,compression,torsion,shearAttheonset-Abeginning;astart:开始：theonsetofacold.感冒初起Offset-Thestartorinitialstage;theoutset.开始，开端,Introduction,Manymaterialsorcomponents,e.g.roadwheelsofacar,wheninservice,aresubjectedtoforcesorloads.Insuchsituationsitisnecessarytoknowthecharacteristicsofthematerialandtodesignthememberfromwhichitismadesuchthatanyresultingdeformationwillnotbeexcessiveandfracturewillnotoccur.Themechanicalbehaviorofamaterialreflectstherelationshipbetweenitsresponseordeformationtoanappliedloadorforce.Importantmechanicalpropertiesarestrength,hardness,ductility,andstiffness.,Materialsandmetallurgicalengineersareconcernedwithproducingandfabricating（制造）materialstomeetservicerequirementsaspredictedbythesestressanalyses.Thisnecessarilyinvolvesanunderstandingoftherelationshipsbetweenthemicrostructure(i.e.,internalfeatures)ofmaterialsandtheirmechanicalproperties.,Tensiontest（拉伸试验）,Whenconstructacomponentorsomethingthelike,allthesepropertiesofmaterialsshouldbetakenintoconsiderationinthewholeprocessofmaterialselectionandstructuredesign.,Stress-straincurveofalowcarbonsteelspecimen,Upperyieldingpoint,Lowyieldingpoint,Definitionofconcepts,Stress（应力）isameasureofanappliedmechanicalloadorforce,normalized(归一化)totakeintoaccountcross-sectionalarea.Twodifferentstressparametersweredefined-engineeringstressandtruestress.,缩截面,标距长度,标准圆形截面拉伸试样,(Engineering)strain（工程应变）,Strainrepresentstheamountofdeformationinducedbyastress;bothengineeringandtruestrainsareused.inwhichl0istheoriginallength（原始长度）beforeanyloadisapplied,andliistheinstantaneouslength（瞬时长度）.Sometimesthequantitylil0isdenotedasl,andisthedeformationelongationorchangeinlengthatsomeinstant,asreferencedtotheoriginallength.Engineeringstrain(subsequentlycalledjuststrain)isunitless（无量纲）,butmeterspermeterorinchesperinchareoftenused.,Modulusofelasticity（弹性模量）,orYoungsmodulus(杨氏模量),Thedegreetowhichastructuredeformsorstrainsdependsonthemagnitudeofanimposedstress.Formostmetalsthatarestressedintensionandatrelativelylowlevels,stressandstrainareproportionaltoeachotherthroughtherelationship=EThisisknownasHookeslaw（虎克定律）,andtheconstantofproportionalityE(GPa)iscalledasmodulusofelasticity（弹性模量）.,Elasticdeformation（弹性变形）,Deformationinwhichstressandstrainareproportionaliscalledelasticdeformation;aplotofstress(ordinate(纵坐标)versusstrain(abscissa（横坐标）)resultsinalinearrelationship,asshowninFigure7.5.TheslopeofthislinearsegmentcorrespondstothemodulusofelasticityE.Stiffnessisamaterialsresistancetoelasticdeformation.Q：Thegreaterthemodulus,thestifferthematerial,orthesmallertheelasticstrainthatresultsfromtheapplicationofagivenstress.(翻译成中文),Plasticdeformation（塑性变形）,Yieldingandyieldingstrength,Yieldingphenomenon（屈服现象）:plasticdeformationbegins,theelasticplastictransitionoccursabruptly.Pointofyielding（屈服点）maybedeterminedastheinitialdeparturefromlinearityofthestressstraincurve;thisissometimescalledtheproportionallimit（比例极限）,asindicatedbypointPinFigure7.10a.aconventionhasbeenestablishedwhereinastraightlineisconstructedparalleltotheelasticportionofthestressstraincurveatsomespecifiedstrainoffset,usually0.002.Thestresscorrespondingtotheintersectionofthislineandthestressstraincurveasitbendsoverintheplasticregionisdefinedastheyieldstrength（屈服强度）y.,Tensilestrength,TensilestrengthTS(MPa)（拉伸强度）isthestressatthemaximumontheengineeringstressstraincurve(Figure7.11).atthismaximumstress,asmallconstrictionorneckbeginstoformatsomepoint,andallsubsequentdeformationisconfinedatthisneck,asindicatedbytheschematicspecimeninsetsinFigure7.11.Thisphenomenonistermednecking（颈缩）.Fracturestrength（断裂强度）correspondstothestressatfracture.,Ductility,Ductility（塑性）isanotherimportantmechanicalproperty.Itisameasureofthedegreeofplasticdeformationthathasbeensustainedatfracture.Ductilitymaybeexpressedquantitativelyaseitherpercentelongation（EL延伸率）tofailureorpercentreductioninarea(RA截面收缩率).Thepercentelongation%EListhepercentageofplasticstrainatfracture,orwherelfisthefracturelengthandl0istheoriginalgaugelengthasabove.,Percentreductioninarea(%RA)isdefinedaswhereA0istheoriginalcross-sectionalareaandAfisthecross-sectionalareaatthepointoffracture.Amaterialthatexperiencesverylittleornoplasticdeformationuponfractureistermedbrittle（脆性）.,TOUGHNESS,Toughness（韧性）isamechanicaltermthatisusedinseveralcontexts;looselyspeaking,itisameasureoftheabilityofamaterialtoabsorbenergyuptofracture.Poissonsratio（柏松比）representsthenegativeratiooftransverse(横向)andlongitudinal（纵向）strains.,Question?,Whatarethetwomethodsforexpressingductility?,Summary,Someofthemechanicalcharacteristicsofmaterialscanbeascertainedbysimplestress-straintests.Therearefourtesttypes:tension,compression,torsion,andshear.Tensilearethemostcommon.Amaterialthatisstressedfirstundergoeselastic,ornonpermanentdeformation,whereinstressandstrainareproportional.Theconstantofproportionalityisthemodulusofelasticityfortensionandcompression,andistheshearmoduluswhenthestressisshear.Possionsratiorepresentsthenegativeratiooftransverseandlongitudinalstrains.,Formetals,thephenomenonofyieldingoccursattheonsetofpla