机械性质与行为

1TheScienceandEngineeringofMaterials,4thed2003DonaldR.Askeland–PradeepP.PhuléChapter6–MechanicalPropertiesandBehavior机械性质与行为2ObjectivesofChapter6Introducethebasicconceptsassociatedwithmechanicalpropertiesofmaterials.介绍与材料机械性质相关的基本概念。Evaluatefactorsthataffectthemechanicalpropertiesofmaterials.评价影响材料机械性质的因素。Reviewsomeofthebasictestingproceduresthatengineersusetoevaluatemanyoftheseproperties.综述一些工程师常用来评价这些性质的基本的检测手段。3ChapterOutline6.1TechnologicalSignificanceofthemechanicalpropertiesofmaterials材料机械性质的科技意义6.2

TerminologyforMechanicalProperties机械性质术语6.3TheTensileTest:UseoftheStress-StrainDiagram拉伸试验：应力-应变图的应用6.4

PropertiesObtainedfromtheTensileTest拉伸试验获得的性质6.5TrueStressandTrueStrain真应力与真应变6.6

TheBendTestforBrittleMaterials脆性材料的弯曲试验6.7HardnessofMaterials材料的硬度6.8

StrainRateEffectsandImpactBehavior应变速度效应和冲击行为4ChapterOutline(Continued)6.9PropertiesObtainedfromtheImpactTest通过冲击试验获得的性质6.10FractureMechanics断裂力学6.11TheImportanceofFractureMechanics断裂力学的重要性6.12MicrostructuralFeaturesofFractureinMetallic

___Materials金属材料断口的微观形貌

6.13MicrostructuralFeaturesofFracturein___Ceramics,Glasses,andComposites___陶瓷，玻璃和复合材料断口的微观形貌

6.14WeibullStatisticsforFailureStrengthAnalysis___韦布尔统计用于断裂强度分析

6.15Fatigue疲劳56.16

ResultsoftheFatigueTest疲劳试验结果6.17ApplicationofFatigueTesting疲劳试验的应用

6.18

Creep,StressRupture,andStressCorrosion___蠕变，应力破断和应力腐蚀

6.19EvaluationofCreepBehavior蠕变行为评价6.20UseofCreepData蠕变数据的利用6.21Superplasticity超塑性ChapterOutline(Continued)6Section6.1TechnologicalSignificanceoftheMechanicalPropertiesofMaterials材料机械性质的科技意义

Figure6.2Thematerialsusedinsportsequipmentmustbelightweight,stiff,tough,andimpactresistant.用于体育器材的材料必须质轻，不易弯曲，坚韧，抗冲击。Figure6.1Aircraft,suchastheoneshownhere,makesuseofaluminumalloysandcarbon-fiber-reinforcedcomposites.例如照片里的飞机，用铝合金和炭纤维增强复合材料制造。7Section6.2TerminologyforMechanicalProperties有关机械性质的术语

Stress-Forceorloadperunitareaofcross-sectionoverwhichtheforceorloadisacting.应力–单位横断面上作用的力或负载。

Strain–Elongationchangeindimensionperunitlength.应变

–单位长度上尺寸的变化。

Young’smodulus-Theslopeofthelinearpartofthestress-straincurveintheelasticregion,sameasmodulusofelasticity.杨氏模量

–在弹性范围内应力-应变曲线线性部分的斜率，等同于弹性模量。

Shearmodulus(G)-Theslopeofthelinearpartoftheshearstress-shearstraincurve.剪切模量

(G)

–剪切应力-剪切应变曲线线性部分的斜率。

Viscosity(η)-Measureofresistancetoflow,definedastheratioofshearstresstoshearstrainrate(unitsPoiseorPa-s).粘度(η)

–对流体阻力的测定，被定义为剪切应力与剪切应变速率的值(单位泊或Pa-s)。

Thixotropicbehavior-Materialsthatshowshearthinningandalsoanapparentviscositythatataconstantrateofsheardecreaseswithtime.触变(摇溶)行为–

材料表现出剪切变稀以及表观粘度在一个恒定的剪切速度下随受剪时间的增加而下降。8Figure6.3(a)Tensile,compressive,shearandbendingstresses.(b)IllustrationshowinghowYoung’smodulusisdefinedforelasticmaterial.(c)Fornonlinearmaterials,weusetheslopeofatangentasavariablequantitythatreplacestheYoung’smodulusconstant(a)拉、压、剪切和弯曲应力。(b)弹性材料杨氏模量的定义(c)对于非线性材料，用一个可变化的切线斜率取代固定的杨氏模量。(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.9Figure6.4(a)Varioustypesofstrainresponsetoanimposedstress.(a)与施加的应力对应的不同种类的应变响应。金属（低于屈服应力），热塑性塑料（低于Tg），热固性塑料，陶瓷和玻璃。易延展的材料超过屈服应力后热塑性塑料在温度接近Tg时黏弹性的：随着应力作用时间的延长，应变逐渐增加，并且恢复较慢；一些粘性的(塑性的)流动也可能发生。10Figure6.4(Continued)(a)Varioustypesofstrainresponsetoanimposedstress.(b)Stressrelaxationinaviscoelasticmaterial.Notethey-axisisstress.Strainisconstant.(a)与施加的应力对应的不同种类的应变响应。(b)在黏弹性材料中应力松弛。弹性的：广泛的弹性应变加部分不可恢复的(塑性)应变。弹性体(橡胶)和部分热塑性塑料当温度超过黏弹性的范围粘性流动：行为像粘性液体，塑性流动随时间增加，当应力消失时有少量弹性应变恢复。蠕变：随时间塑性应变增加，当应力消失，部分弹性应变恢复。应变是一个常数，应力随时间下降。11(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.5ShearstressstrainraterelationshipsforNewtonianandnon-Newtonianmaterials牛顿和非牛顿流体的剪切应力与应变速率之间的关系。宾汉体(塑性体)(也是剪切变稀)剪切变稀剪切变稠

牛顿流体屈服应力下剪切变稀屈服应力下剪切变稠12Section6.3TheTensileTest:UseoftheStress-StrainDiagram拉伸试验：应力-应变图的应用Load-Theforceappliedtoamaterialduringtesting.负载–试验时施加到材料上的力。StraingageorExtensometer-Adeviceusedformeasuringchangeinlengthandhencestrain.应变计量器或伸长计

用于测定长度变化的装置，从而确定应变。Glasstemperature(Tg)-Atemperaturebelowwhichanductilematerialbehavesasifitisbrittle.玻璃化温度(Tg)

–

当低于此温度时具有延展性的材料的行为就像脆性材料。Engineeringstress-Theappliedload,orforce,dividedbytheoriginalcross-sectionalareaofthematerial.工程应力

–

所施加的负载或力除以材料的横断面积。Engineeringstrain-Theamountthatamaterialdeformsperunitlengthinatensiletest.工程应变–在拉伸试验中材料单位长度变形的量。13(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.7Aunidirectionalforceisappliedtoaspecimeninthetensiletestbymeansofthemoveablecrosshead.Thecross-headmovementcanbeperformedusingscrewsorahydraulicmechanism在拉伸试验中借助于可移动的滑块将单向力施加到试样上。滑块的移动可通过螺杆或水压机进行。14(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.9Tensilestress-straincurvesfordifferentmaterials.Notethatthesearequalitative不同材料的拉伸应力-应变曲线。注意这些是定性的。1516(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.10Thestress-straincurveforanaluminumalloyfromTable6-1铝合金的应力-应变曲线（来源于表6-1）弹性伸长条件屈服强度补偿屈服强度偏置屈服强度

断裂伸长17Figure6.10Thestress-straincurveforanaluminumalloyfromTable6-1有的金属材料的屈服点极不明显,在测量上有困难,因此为了衡量材料的屈服特性,规定产生永久残余塑性变形等于一定值(一般为原长度的0.2%)时的应力,称为条件屈服强度或简称屈服强度σ0.2

1819Section6.4PropertiesObtainedfromtheTensileTest通过拉伸试验获得的性质

Elasticlimit弹性极限Tensilestrength,Necking抗拉强度，(拉力试验)缩颈(现象)Hooke’slaw虎克定律Poisson’sratio泊松比(Er)

Modulusofresilience(Er)回弹模量Tensiletoughness拉伸韧性Ductility展延性20(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.11(a)Determiningthe0.2%offsetyieldstrengthingraycastiron,and(b)upperandloweryieldpointbehaviorinalow-carbonsteel.(a)确定灰铸铁的0.2%条件屈服强度，(b)在低碳钢中存在的较高和较低屈服点。21(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.12Localizeddeformationofaductilematerialduringatensiletestproducesaneckedregion.Themicrographshowsneckedregioninafracturedsample.具有延展性的材料在拉伸试验中的局部变形是产生收缩的区域。显微照片显示断裂试样中收缩的区域。22Figure6.13Typicalyieldstrengthvaluesfordifferentengineeredmaterials.PMMA

聚甲基丙烯酸甲酯(=polymethylmethacrylate)23泊松比：材料受拉伸或压缩力时，横向变形量与纵向变形量的比值。

24(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.14Comparisonoftheelasticbehaviorofsteelandaluminum.Foragivenstress,aluminumdeformselasticallythreetimesasmuchasdoessteel.在給定的应力下比较钢和铝的弹性行为，铝的弹性变形是钢的三倍。25Figure6.15Rangeofelasticmodulusfordifferentengineeredmaterials.不同工程材料的弹性模量范围。26(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.16Theeffectoftemperance(a)onthestress-straincurveand(b)onthetensilepropertiesofanaluminumalloy.(a)温度对应力应变曲线的影响(b)温度对铝合金拉伸性能的影响。27Section6.5TrueStressandTrueStrain真应力和真应变

TruestressTheloaddividedbytheactualcross-sectionalareaofthespecimenatthatload.真应力负载除以试样在该负载下的实际的截面积。TruestrainThestraincalculatedusingactualandnotoriginaldimensions,givenbyεt=ln(l/l0).真应变

用实际的而不是用原始的尺寸计算的应变，由εt=ln(l/l0)计算.

(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.17Therelationbetweenthetruestress-truestraindiagramandengineeringstress-engineeringstraindiagram.Thecurvesareidenticaltotheyieldpoint.真应力-真应变曲线与工程应力-工程应变曲线的关系，在屈服点之前两者是重合的。28Example6.1TrueStressandTrueStrainCalculation真应力和真应变CompareengineeringstressandstrainwithtruestressandstrainforthealuminumalloyinExample6.1at(a)themaximumloadand(b)fracture.Thediameteratmaximumloadis0.497in.andatfractureis0.398in.比较铝合金的工程应力应变和真应力应变(a)在最大负载处(b)在断裂处。试样初始直径为0.505吋，在最大负载处试样直径为0.497吋，在断裂处试样直径为0.398吋。Example6.1SOLUTION29Example6.1SOLUTION(Continued)30Section6.6TheBendTestforBrittleMaterials脆性材料的弯曲试验

Bendtest-Applicationofaforcetothecenterofabarthatissupportedoneachendtodeterminetheresistanceofthematerialtoastaticorslowlyappliedload.弯曲试验–一根棒状试样两端固定，在试样的中间施加一个力，确定材料对静载荷或缓慢施加的载荷的抵抗力。Flexuralstrengthormodulusofrupture-Thestressrequiredtofractureaspecimeninabendtest.挠曲强度或断裂模数(抗折强度)-在弯曲试验中使试样断裂所需要的应力。Flexuralmodulus-Themodulusofelasticitycalculatedfromtheresultsofabendtest,givingtheslopeofthestress-deflectioncurve.挠曲模量

–由弯曲试验结果计算出的弹性模量，由应力-挠度曲线的斜率給出。31(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.18Thestress-strainbehaviorofbrittlematerialscomparedwiththatofmoreductilematerials.脆性材料的应力-应变行为与更具有延展性的材料比较。32(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.19(a)Thebendtestoftenusedformeasuringthestrengthofbrittlematerials,and(b)thedeflectionδobtainedbybending.(a)弯曲试验往往用于检测脆性材料(b)因弯曲而得到的挠度δ33(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.20Stress-deflectioncurveforMagnesiumoxide(MgO）obtainedfromabendtest.MgO进行弯曲试验时得到的应力-挠度曲线34(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.21(a)Threepointand(b)four-pointbendtestsetup.(a)三点和(b)四点弯曲试验装置最大挠矩=FLs/4最大挠矩=FL1/23536Section6.7HardnessofMaterials材料的硬度

Hardnesstest-Measurestheresistanceofamaterialtopenetrationbyasharpobject.硬度测试-

测试材料对尖锐物体穿透的抵抗力。Macrohardness-Overallbulkhardnessofmaterialsmeasuredusingloads>2N.宏观硬度

–用大于2N的负载测试的材料整体的硬度Microhardness–Hardnessofmaterialstypicallymeasuredusingloadslessthan2NusingsuchtestasKnoop(HK).显微硬度

–

采用类似努普显微压痕硬度试验仪，典型的测试是用小于2N的负载测试的材料硬度。Nano-hardness-Hardnessofmaterialsmeasuredat1–10nmlengthscaleusingextremelysmall(~100µN)forces.纳米-硬度

–

用非常小的力(~100µN)在1–10nm长度范围测试材料的硬度。37(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.23IndentorsfortheBrinellandRockwellhardnesstests用于布氏硬度和洛氏硬度试验的压锥（压头）3839Section6.8StrainRateEffectsandImpactBehavior应变速度效应和冲击行为

Impacttest-Measurestheabilityofamaterialtoabsorbthesuddenapplicationofaloadwithoutbreaking.冲击试验–测试材料吸收突然施加的负载而不断裂的能力。Impactenergy-Theenergyrequiredtofractureastandardspecimenwhentheloadisappliedsuddenly.冲击能–当负载突然施加到标准试样上，使标准试样断裂所需要的能量。Impacttoughness-Energyabsorbedbyamaterial,usuallynotched,duringfracture,undertheconditionsofimpacttest.冲击韧性–在抗冲击试验条件下，材料在断裂过程中吸收的能量，材料通常带有切口。Fracturetoughness–Theresistanceofamaterialtofailureinthepresenceofaflaw.断裂韧度

–

当材料中存在裂纹时材料抵抗断裂的能力。40(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.26Theimpacttest:(a)TheCharpyandIzodtests,and(b)dimensionsoftypicalspecimens.冲击试验：(a)夏比试验和埃左德试验（摆锤冲击试验）(b)典型试样的尺寸。41Section6.9PropertiesObtainedfromtheImpactTest通过冲击试验获得的性质Ductiletobrittletransitiontemperature(DBTT)-Thetemperaturebelowwhichamaterialbehavesinabrittlemannerinanimpacttest.展延性到脆性转变温度(DBTT)–在冲击试验中低于该温度时材料的行为是脆性的。Notchsensitivity-Measurestheeffectofanotch,scratch,orotherimperfectiononamaterial’sproperties,suchastoughnessorfatiguelife.切口敏感性

–测试切口、划伤、或其它缺陷对材料性质的影响，例如韧性或疲劳寿命。42(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.27ResultsfromaseriesofIzodimpacttestsforasuper-toughnylonthermoplasticpolymer.对超强韧尼龙热塑性高分子进行一系列埃左德试验的结果。43(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.28TheCharpyV-notchpropertiesforaBCCcarbonsteelandaFCCstainlesssteel.TheFCCcrystalstructuretypicallyleadstophigherabsorbedenergiesandnotransitiontemperature.一种BCC碳钢和一种FCC不锈钢夏比V-形切口的性能。面心立方结构代表性地导致更高的能量吸收，而且没有转变温度。44(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.29Theareacontainedwithinthetruestress-truestraincurveisrelatedtothetensiletoughness.AlthoughmaterialBhasaloweryieldstrength,itabsorbsagreaterenergythanmaterialA.Theenergiesfromthesecurvesmaynotbethesameasthoseobtainedfromimpacttestdata.真应力-真应变曲线曲线下的面积与拉伸韧性有关。虽然材料B的屈服强度较低，但比材料A吸收的能量多。通过这些曲线得到的能量与冲击试验获得的结果不一定相同。45Section6.10FractureMechanics断裂力学

Fracturemechanics-Thestudyofamaterial’sabilitytowithstandstressinthepresenceofaflaw.断裂力学–研究材料中存在裂纹时材料承受应力的能力。Fracturetoughness-Theresistanceofamaterialtofailureinthepresenceofaflaw.断裂韧度

–当材料中存在裂纹时材料抵抗断裂的能力。46(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.30Schematicdrawingoffracturetoughnessspecimenswith(a)edgeand(b)internalflaws.断裂韧度试样的示意图，(a)裂纹处于试样边沿，(b)裂纹处于试样内部。47(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.31ThefracturetoughnessKc

ofa3000,000psiyieldstrengthsteeldecreaseswithincreasingthickness,eventuallylevelingoffattheplanestrainfracturetoughnessKlc一种屈服强度为3000,000psi的钢材随厚度的增加断裂韧度Kc下降，最后在平面应变断裂韧度Klc处稳定下来。平面应变断裂韧度Klc是含裂纹线弹性材料抵抗裂纹扩展能力的度量,是衡量材料断裂性能的重要指标。4849Figure6-33AscanningelectronmicrographshowingcrackpropagationinaPZTceramic.PZT陶瓷中裂纹发展的扫描电镜照片。Figure6-32Secondarycracksdevelopedduringhardnesstestingcanbeusedtoassessthefracturetoughnessofbrittlematerials.硬度测试过程中二级裂纹的发展能用于评价脆性材料的断裂韧度。50Figure6-34Fracturetoughnessversusstrengthofdifferentengineeredmaterials.不同工程材料的断裂韧度与强度。51Section6.11TheImportanceofFractureMechanics断裂力学的重要性

SelectionofaMaterial材料的选择DesignofaComponent元件的设计DesignofaManufacturingorTestingMethod制造方法和检测手段的设计Griffithflaw-Acrackorflawinamaterialthatconcentratesandmagnifiestheappliedstress.格里菲思微裂纹

–材料中的裂缝或裂纹集中并放大所施加的应力。52(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.35SchematicdiagramoftheGriffithflawinaceramic.陶瓷中格里菲思微裂纹示意图。53Section6.12MicrostructuralFeaturesofFractureinMetallicMaterials金属材料断口的微观形貌

Transgranular-Meaningacrossthegrains(e.g.,atransgranularfracturewouldbefractureinwhichcrackswouldgothroughthegrains).穿晶

–意味着穿过晶体颗粒（例如，穿晶断裂是指断裂穿过了晶体颗粒）Microvoids-Developmentofsmallholesinamaterial.微孔

–材料中小孔的发展。Intergranular-Inbetweengrainsoralongthegrainboundaries.晶粒间的

–在颗粒之间或沿着晶粒边界。Chevronpattern-Acommonfracturefeatureproducedbyseparatecrackfrontspropagatingatdifferentlevelsinthematerial.∨型图案

–一种常见的断裂面形貌，产生于分开的裂纹前沿不同平面发展。54(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.36Whenaductilematerialispulledinatensiletest,neckingbeginsandvoidsform–startingnearthecenterofthebar–bynucleationatgrainboundariesorinclusions.Asdeformationcontinuesa45°shearlipmayform,producingafinalcupandconefracture.当有延展性的材料在拉伸试验中承受拉力时，颈缩开始而且孔洞形成–从棒的中心附近开始–起因是晶界上晶核形成或夹杂物引起。因为变形呈45°延伸而形成剪切唇，最终形成杯形和锥形断裂面。剪切唇

微孔合并55(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.37Dimplesformduringductilefracture.Equiaxeddimplesforminthecenter,wheremicrovoidsgrow.Elongateddimples,pointingtowardtheoriginoffailure,formontheshearlip.塑性断裂过程中断口波纹的形成。中间形成各个方向大小近似的微凹，在这里微孔增大，在剪切唇上形成拉长的微凹波纹，波纹的方向指向断裂起始点。椭圆形波纹圆的，各个方向大小近似的微凹56(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.38Scanningelectronmicrographsofanannealed1018steelexhibitingductilefractureinatensiletest.(a)Equiaxeddimplesattheflatcenterofthecupandcone,and(b)elongateddimplesattheshearlip(x1250)退火1018钢材扫描电镜照片，在拉伸试验中显示延展性断口。(a)在杯形和锥形中间的平面上各个方向大小近似的微凹，(b)在剪切唇上形成拉长的微凹波纹(x1250)。57Figure6.39Scanningelectronmicrographofabrittlefracturesurfaceofaquenched1010steel(x5000).淬火1010钢材脆性断裂断口表面的扫描电镜照片(x5000).

58(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.40TheChevronpatternina0.5-in.-diameterquenched4340steel.Thesteelfailedinabrittlemannerbyanimpactblow.一个0.5-in.直径经淬火的4340钢材断裂面的∨型图案，该材料在冲击时以脆性方式断裂。裂纹起始点59(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.41TheChevronpatternformsasthecrackpropagatesfromtheoriginatdifferentlevels.Thepatternpointsbacktotheorigin.裂纹在不同的平面从起始点开始发展形成的∨型图案，∨型图案的尖端集中在起始点。60Example6.12AutomobileAxleFailureAnalysis汽车车轴断裂原因分析Anengineerinvestigatingthecauseofanautomobileaccidentfindsthattherightrearwheelhasbrokenofattheaxle.Theaxleisbent.ThefracturesurfacerevealsaChevronpatternpointingtowardthesurfaceoftheaxle.Suggestapossiblecauseforthefracture.一名工程师调查一起交通事故的原因，发现右后轮轴断裂，该轴已经弯曲，断裂口表面显示∨型图案指向轴的表面。提出引起断裂的可能原因。Example6.12SOLUTIONTheChevronpatternindicatesthatthewheelwassubjectedtoanintenseimpactblow,whichwastransmittedtotheaxle,causingfailure.∨型图案提示该车轮曾遭受强烈的冲击，冲击传递到车轴导致车轴断裂。Furtherexaminationofthefracturesurface,microstructure,composition,andpropertiesmayverifythattheaxlewasmanufacturedproperly.对断口表面，微观结构，化学组成以及材料性质的进一步检查可能核实这个车轴在制造上没有问题。61Section6.13MicrostructuralFeaturesofFractureinCeramics,Glasses,andComposites陶瓷，玻璃和复合材料断口的微观形貌

Conchoidalfracture-Fracturesurfacecontainingaverysmoothmirrorzoneneartheoriginofthefracture,withtearlinescomprisingtheremainderofthesurface.贝壳状断裂

–在断口表面靠近断裂起始点的位置存在非常平滑的镜面区域，表面剩余的部分则由撕裂纹条组成。Delamination-Theprocessbywhichdifferentlayersinacompositewillbegintodebond.剥离

–复合材料中不同的层在该过程中开始分离。62(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.42Scanningelectronmicrographsoffracturesurfacesinceramics.(a)ThefracturesurfaceAl203,showingthecleavagefaces(x1250),and(b)thefracturesurfaceofglass,showingthemirrorzone(top)andtearlinescharacteristicofconchoidalfracture(x300).陶瓷断口的扫描电镜照片。(a)Al203断口表面，显示劈裂表面(x1250),(b)玻璃断口表面，显示镜面区域（顶部）和撕裂纹条表现出贝壳状断裂特征(x300)。63(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.43Fiber-reinforcedcompositescanfailbyseveralmechanisms.(a)Duetoweakbondingbetweenthematrixandfibers,fiberscanpulloutofthematrix,creatingvoids.(b)iftheindividuallayersofthematrixarepoorlybonded,thematrixmaydelaminate,creatingvoids纤维增强复合材料可以通过数种机制失效。(a)因为基体与纤维之间较弱的结合，纤维能从基体中拔出并产生产空洞。(b)基体的各层之间结合力差，基体材料可能剥离并产生产空洞。64Example6.13FractureinComposites复合材料断裂Describethedifferenceinfracturemechanismbetweenaboron-reinforcedaluminumcompositeandaglassfiber-reinforcedepoxycomposite.描述硼增强铝复合材料与玻璃纤维增强环氧树脂复合材料之间断裂机制的差别。Example6.13SOLUTIONIntheboron-aluminumcomposite,thealuminummatrixissoftandductile;thusweexpectthematrixtofailinaductilemanner.Boronfibers,incontrast,failinabrittlemanner.Bothglassfibersandepoxyarebrittle;thusthecompositeasawholeshoulddisplaylittleevidenceofductilefracture.在硼增强铝复合材料中，铝基体柔软且有延展性，因此我们预期基体失效的方式为延展性断裂，与之对比，硼纤维断裂是脆性的。玻璃纤维和环氧树脂都是脆性断裂方式，这样整个复合材料显示少许延展性断裂的迹象。65Section6.14WeibullStatisticsforFailureStrengthAnalysis韦布尔统计用于断裂强度分析

Weibulldistribution-Amathematicaldistributionshowingtheprobabilityoffailureorsurvivalofamaterialasafunctionofthestress.韦布尔分布

–表示材料失效或有效随应力变化的概率分布。66(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.44TheWeibulldistributiondescribesthefractionofthesamplesthatfailatanygivenappliedstress.描述在任意给定应力下失效样品分数的韦布尔分布67Example6.14钢和氧化铝陶瓷的韦布尔模数WeibullModulusforSteelandAluminaCeramicsFigure6.45showsthelog-logplotsoftheprobabilityoffailureandstrengthofa0.2%plaincarbonsteel,analuminaceramicspreparedusingconventionalpowderprocessinginwhichaluminapowdersarecompactedinapressandsinteredintoadensemassathightemperature.Also,includedisaplotforaluminaceramicspreparedusingspecialtechniquesthatleadstomuchmoreuniformandcontrolledparticlesize.Thisinturnminimizestheflaws.Thesesamplesarelabeledascontrolledparticlesize(CPS).Commentonthenatureofthesegraphs.图6.45显示断裂可能性的对数值和强度的关系，材料包括含碳0.2%的普通碳素钢，一种用常规粉末法制备的氧化铝陶瓷，制备过程中氧化铝粉末经压实后再高温烧结成致密体。还有一种氧化铝陶瓷是用特殊的方法制备，这种方法导致非常高的均匀性并控制了颗粒尺寸，这使得裂纹减少到最低程度，这些样品被标记为(CPS).评论这些图的特性。68Figure6.45AcumulativeplotoftheprobabilitythatasamplewillfailatanygivenappliedstressyieldstheWeibullmodulusorslope.Aluminaproducedbytwodifferentmethodsiscomparedwithlowcarbonsteel.GoodreliabilityisobtainedforahighWeibullmodulus.在任意给定应力下试样断裂可能性累计图，从中可获得韦布尔模数或斜率。两种不同方法制备的氧化铝与低碳钢进行比较。高的韦布尔模数具有高的可靠性。韦布尔模数=9.7韦布尔模数=4.769Example6.14SOLUTIONForplaincarbonsteelthelineisalmostvertical(i.e.,slopeormvalueisessentiallyapproachinglargevalues).Thismeansthatthereisverylittlevariation(5to10%)inthestrengthofdifferentsamplesofthe0.2%Csteel.对于普通碳素钢，线几乎是垂直的（即斜率或m值实际上接近最大值）。这意味着含碳0.2%的钢材不同的样品的强度变化非常小(5to10%)。Foraluminaceramicspreparedusingtraditionalprocessing,thevariabilityishigh(i.e.,mislow~4.7).对于用常规工艺制备的氧化铝陶瓷，不同的样品的强度变化大(即,m低~4.7).

Forceramicspreparedusingimprovedandcontrolledprocessingtechniquesthemishigher~9.7indicatingamoreuniformdistributionofflaws.Theaveragestrengthisalsohigher(~578MPa)suggestinglessernumberofflawsthatwillleadtofracture.对于用特殊工艺制备的氧化铝陶瓷，m较高~9.7，表明裂纹分布更均一。其平均强度也较高(~578MPa)，提示导致断裂的裂纹数量更少。70Section6.15Fatigue疲劳Fatigue-istheloweringofstrengthorfailureofamaterialduetorepetitivestresswhichmaybeaboveorbelowtheyieldstrength.疲劳–

由于重复应力（可能高于或低于屈服强度）作用使材料呈低强度或失效。Creep–Atimedependent,permanentdeformationathightemperatures,occurringatconstantloadorconstantstress.蠕变

–由时间决定，在恒定的负载或应力作用下，在高温下产生的永久形变。Beachorclamshellmarks-Patternsoftenseenonacomponentsubjectedtofatigue.海滩纹或蚌壳纹

–在承受疲劳应力的元件上经常出现图案。Rotatingcantileverbeamtest-Anoldertestforfatiguetesting.悬臂梁弯曲疲劳试验

–用于疲劳试验的老方法。S-Ncurve(alsoknownastheWöhlercurve)-Agraphshowingstressasafunctionofnumberofcyclesinfatigue.S-N曲线(或称为Wöhler曲线)-应力与循环荷载次数之间的函数关系。71Figure6.47Fatiguefracturesurface.(a)Atlowmagnifications,thebeachmarkpatternindicatesfatigueasthefracturemechanism.Thearrowsshowthedirectionofgrowthofthecrackfront,whoseoriginisatthebottomofthephotograph.(b)Atveryhighmagnifications,closelyspacedstriationsformedduringfatigueareobserved(x1000).疲劳断口表面。(a)在低倍率下，海滩纹图案显示疲劳作为断裂机理。箭头显示裂纹前缘发展的方向，它们的起点在照片的底部。(b)在非常高的放大倍数下，观察到疲劳而产生的密集的条纹(x1000)。72(c)2003Brooks/Cole,adivisionofThomsonLearning,Inc.ThomsonLearning™isatrademarkusedhereinunderlicense.Figure6.48Schematicrepresentationofafatiguefracturesurfaceinasteelshaft,showingtheinitiationregion,thepropagationoffatiguecrack(withbeammarkings),andcatastrophicrupturewhenthecracklengthexceedsacriticalvalueattheappliedstress.钢轴疲劳