专业英语阅读.ppt

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1、专业英语阅读胡莉莉华中科技大学 力学系Email:Cell:158027101602009 秋季工程力学 2007级 01 02 班Course ArrangementReference readingResearch articles on specific topicsComprehensive presentationExamination from two sides:presentation as a presenter;involvement as an audienceFinal credit consists of 20%class involvement+40%present

2、ation credit+40%written translationsPresentationStart from 3rd class,2 presentations each timeGroup work required4-5 people in each group,12 groups in totalIn each group,i.e.some responsible for the presentation,some responsible for answering questionsInvolvement from audience will earn extra credit

3、s Order of presentations could be volunteered or specifiedReference ratedPresentation FlowIntroduce yourselfIntroduce your topic and the authors of the paperName,university/institute,year published,journal publishedProvide an outline of the whole presentationOne slidee.g.introduction,experimental/si

4、mulation procedure,results,discussion,conclusionBackground of the problem studiedMethodology:how to study the problemConclusions obtainedSample OutlineMotivationImportance of cell adhesion Existing cell adhesion measurement techniquesLaser-induced stress wave techniqueExperimental SetupSample Prepar

5、ationExperimental ResultsObservation of cell decohesion Quantitative adhesion measurementConclusion and DiscussionRequirementsEnglish speakingChinese explanation Try to have more graphics than sentences on the slidesNotes are allowed during the presentation最多三人讲，一共15分钟，不可超时页面上满页的文字不允许，要通过自己讲解主要基于文章的

6、内容，可扩展，不可删减可使用卡片，记录要点MechanicsTheoretical Mechanics 理论力学Material Mechanics 材料力学Composite Materials Mechanics 复合材料力学Fluid Mechanics 流体力学Structure Mechanics 结构力学Fracture Mechanics 断裂力学Elastic Mechanics 弹性力学Continuum Mechanics 连续介质力学Quantum Mechanics 量子力学MechanicalSimulations:Solid,Fluid;BioMechanics;S

7、oilMechanics;ArchitecturalMechanics.TopicsEngineering Simulations 工程计算Experimental Mechanics 力学实验BioMechanics 生物力学Material Mechanics 材料力学Small Scale Mechanics 微尺度力学Fluid Mechanics 流体力学Frequently Used WordsUnits(单位)：Distance:kilo-meter(km),meter(m),milli-meter(mm),micro-meter(mm),nano-meter(nm),pico-

8、meter(pm)inch,foot,mileTime:second(s),minute(m),hour(h),day,year milli-second(ms),micro-second(ms),nano-second(ns),pico-second(ps),femto-second(fs),atto-second(as)Temperature:degree centigrade(),Fahrenheit(F),Kelvin(K)Force:Newton(N),Stress:Pascal(Pa),mega-Pascal(MPa),giga-Pascal(GPa)bar,torr,atmosp

9、here(atm)StrainPrefix&Suffixdiffer different difference differentiateconduct conductivity superconductivity;supersonic;superposition;supercomputer Method methodologySolid solidifyMechanics mechanical Biomechanics mechatronics mechanism mechanicalism mechanicallyfoamed plasticExample:Mechanical Behav

10、ior of MaterialsMechanical Behavior of Materials,by Thomas H.CourtneyOriginal edition published in 1990 in USPhotocopies available in 2004 in ChinaOutlineElastic deformationPermanent deformationThe tension testStrain-rate sensitivityYielding under multiaxial loading conditionsMohrs circleThe hardnes

11、s testThe torsion testFractureFracture toughnessTensile fractureCreep fractureFatigue fractureEmbrittlementSummarySection 1.1 IntroductionThis book deals with the mechanical behavior of solids,particularly as this behavior is affected by processes taking place at the microscopic and/or atomic level.

12、The response of a solid to external or internal forces can vary considerably,depending on the magnitude of these forces and the material characteristics.For example,if the forces are great the material may fracture.Lesser values of force may result in material permanent deformation without fracture

13、and,if the forces are low enough,the material may deform only in an elastic way.The treatment of mechanical behavior in this book closely parallels these three possibilities.Al5%-Cualloy:coolingrate10/sAl5%-Cualloy:coolingrate1/sSome Important Words Fracture 断裂Elastic deformation 弹性变形External force

14、外力Internal force 内力Microscopic 微观Atomic level 原子水平Magnitude 幅值Force 力Permanent deformation 永久变形While our aim is to relate the mechanical behavior of a solid to material structure at the microscopic and atomic level,this response is manifested macroscopically.Thus,to fulfill adequately the objective

15、of this text,a reasonable background in the concepts of mechanical behavior as measured and assessed at a macroscopic level is required.Indeed,it is this coupling between material microstructure and bulk properties that constitutes one of the most fruitful areas of materials science and engineering.

16、Some Important Words Macroscopic 宏观 microscopic 微观Coupling 耦合Microstructure 微观结构Bulk properties 整体性质Section 1.2 Elastic DeformationWhen a solid is subjected to external forces,it undergoes a change in shape.When the load is released,the shape may not returned to what is was prior to the application

17、of the force;under these circumstances we say that the material has deformed permanently.Forces less than those that cause permanent deformation deform the solid elastically;that is,when the force is subsequently removed the body assumes the dimensions it had prior to its application.The elastic beh

18、avior of many materials can be represented by a form of Hookes law.The extension of a sample is linear related to the force.The extension also depends on sample dimensions.For example,doubling of initial sample length leads to a doubling of the extension,whereas if the sample cross-sectional area no

19、rmal to the applied force is doubled,the extension is halved.l+DlF FF FF FF FF F2l+2Dll+Dl/2F FAA2ASome Important Words Extension 伸长 external force 外力Cross-sectional area 横截面积Normal 法向，normal to垂直,perpendicularParallel 平行This equation is often written in normalized form of stress and strain,with E t

20、he Youngs modulus or tensile modulus.A material having a high value of the tensile modulus is stiff;i.e.,it is resistant to tensile deformation of the kind just described.Linear elasticity of this kind is observed in all classes of solids.It is the dominant mode of elastic deformation in all solids

21、at low temperatures,in crystalline solids and inorganic glasses up to moderately high temperatures,and in noncrystalline polymers at low temperatures.The extent of linear elasticity is usually quite limited;that is,most materials are capable of being linearly elastically extended only to strains on

22、the order of several tenths of a percent.Linear elasticity represents the stretching(or compression/distortion)of atomic bonds,and for this reason E is a measure of a materials bond strength.Some Important WordsNormalize 归一化Tensile modulus 拉伸模量；Youngs modulus 杨氏模量Tensile test 拉伸实验Stiff 硬；stiffness 硬

23、度crystalline solid 晶体Inorganic glass 无机玻璃noncrystalline polymers 非晶态聚合物Stretching/compression/distortion 拉伸/压缩/扭曲Atomic bonds 原子键A change in material shape can also be caused by shear stresses.These cause relative displacement of the upper and lower surfaces of the solid illustrated.The shear strain

24、 and shear stress are related through,with G the shear modulus.In a physical sense G can be viewed as a measure of the resistance to bond distortion within a solid.This can be visualized by considering the simple-cubic single crystal.The change in atomic positions due to the shear stress results fro

25、m“bending”of atomic bonds.Some Important WordsShear stress 剪切应力Shear strain 剪切应变Relative displacement 相对位移Position 位置Almost all classes of solids also exhibit,at least over a certain temperature range,nonlinear and time-dependent elasticity.This viscoelasticity,as it is called,is most common to nonc

26、rystalline polymers,but also occurs to a much more limited extent in crystalline solids and inorganic glasses.The strain in a linear elastic solid is a single-valued function of the stress;that is,the loading and unloading segments of the-relationship in a viscoelastic material depends on the sense

27、of loading.Moreover,the level of stress attained depends,too,on the rate at which a viscoelastic material is stretched(the strain rate).With increasing strain rate a viscoelastic material becomes stiffer;for example,the“average”modulus(1/1)increases with strain rate.Viscoelastic behavior is also man

28、ifested by a strain that varies with time under conditions of a constant applied stress.That is,upon initial application of the stress some instantaneous(linear elastic)strain is first experienced,following which the material continue to extend,with the strain approaching some asymptotic value.On re

29、moval of the load,the linear elastic strain is instantaneously,and the viscoelastic strain sluggishly,recovered.loadingunloadingloadingunloadinge1s1e1s1Some Important WordsViscoelasticity 粘弹性Single-value function 单值函数 Loading/unloading 加载/缷载Strain rate 应变率Linear elastic 线弹性Nonlinear elasticity,of wh

30、ich viscoelasticity is one example,need not be time-dependent.For example,nonlinear time-independent elasticity is observed in certain fine,strong crystalline solids called whiskers.Whiskers typically have diameters on the order of micrometers,and when stretched in tension they deform in a linear el

31、astic way up to strains on the order of half a percent.For elastic strains in excess of this(whiskers are capable of such strains)the-relationship is nonlinear.An extreme example of nonlinear time-independent elasticity is found in elastomers.These are a special class of polymers that over a limited

32、 temperature range are capable of demonstrating extensive elastic strains(up to a thousand percent or so).This rubber elasticity is quite different from linear elasticity,which is as mentioned,ordinarily limited and,as might be expected,the causes of rubber elasticity differ fundamentally from those

33、 of linear elasticity.Some Important WordsWhisker 须晶Elastomer 高弹性体，人造橡胶Rubber 橡胶Some Important Words Fracture 断裂Elastic deformation 弹性变形External force 外力Internal force 内力Microscopic 微观Atomic level 原子水平Magnitude 幅值Force 力Permanent deformation 永久变形Some Important Words Macroscopic 宏观 microscopic 微观Coup

34、ling 耦合Microstructure 微观结构Bulk properties 整体性质Some Important WordsNormalize 归一化Tensile modulus 拉伸模量；Youngs modulus 杨氏模量Tensile test 拉伸实验Stiff 硬；stiffness 硬度crystalline solid 晶体Inorganic glass 无机玻璃noncrystalline polymers 非晶态聚合物Stretching/compression/distortion 拉伸/压缩/扭曲Atomic bonds 原子键Some Important W

35、ordsShear stress 剪切应力Shear strain 剪切应变Relative displacement 相对位移Position 位置Some Important WordsViscoelasticity 粘弹性Single-value function 单值函数 Loading/unloading 加载/缷载Strain rate 应变率Linear elastic 线弹性Some Important WordsWhisker 须晶Elastomer 高弹性体，人造橡胶Rubber 橡胶Section 1.3 Permanent DeformationA materials

36、response to uniaxial loading is assessed most often by means of a tension test.Force is measured with a load cell(often a calibrated,stiff spring);extension is measured by extensometer.Some materials(brittle ones)manifest only macroscopic elastic deformation up to the stress at which they fracture.E

37、xamples include inorganic glasses,polycrystalline ceramics at room temperature,and some metals and their alloys at low temperatures.Most metals at ordinary temperatures,and many ceramics at high temperatures,deform permanently before fracture.36soykeelastic yield work hardenneckingT.S.Some Important

38、 WordsLoad cell 测压元件Calibrate 标定Extensometer 变形测定器;张量计Brittle 脆性Polycrystalline 多晶材料Metals and alloys 金属及合金Some Important Words Extension 伸长 external force 外力Cross-sectional area 横截面积Normal 法向，normal to垂直,perpendicularParallel 平行Section 1.3 Permanent DeformationWork hardeningFollowing yielding,the s

39、tress required for further plastic flow(the flow stress)increase with increasing strain.The positive slope of the stress-strain curve indicates that the material is made more resistant to plastic deformation by virtue of the deformation itself.During plastic deformation,if the deformation is uniform

40、 along the sample length True stressEngineering stress39soykeelastic yield work hardenneckingT.S.Some Important WordsWork hardening 应变强化True stress 真实应力Engineering stress 工程应力Engineering strain by definition is overestimated.True strain is based on instantaneous sample length.It can be approximated

41、by considering the total strain to result from a series of small,incremental extensions.Express in differential form Integrate from l0 to liThe constant-volume condition of plastic deformation allows relationships to be developed among stress and strainFor a tensile testFor compression test,the rela

42、tion will be oppositeThe difference between the true and engineering stresses and strains increases with plastic deformation.Thus,at low strains,so in discussion of elastic deformation,there is no need to differentiate between engineering and true stress and strain.The tensile point is associated wi

43、th a geometrical instability,and not with a fundamental alteration in material behavior.Each and every tensile bar has inhomogeneities along its length;either within it(e.g.small inclusions or porosity)or on its surface(e.g.machining marks or a taper along the bar surface).Strain is localized in the

44、se regions,and this leads to a locally greater reduction in area.For strains less than the tensile point,the increase in flow stressaccompanying the greater strains is large enough to lead to removal of the incipient instability.This process occurs regularly and repeatedly during tensile loading,and

45、 could be monitored if sufficiently accurate instrumentation were available.The rate of work hardening decreases as deformation continues;that is,the increase in flow stress per unit strain becomes less with increasing strain.Thus,it becomes progressively more difficult to work harden an incipient i

46、nstability sufficiently to remove it.As the tensile point,the work-hardening capacity has been diminished enough that an instability once formed continues to develop.The criterion for necking is related to the materials work hardening tendencies v.s.those that initiate instability.The criterion can

47、be expressed quantitatively by realizing that at T.S.the engineering stress or equivalently,the force reaches a maximumAnother measure of material ductility is reduction in area at fracture,usually expressed as percent R.A.The final cross-sectional area is measured as the area of the neck following

48、fracture.Since%R.A.is independent of sample gage length,it is more of a material property than percent elongation.As a result of the nonuniform deformation following the onset of necking,true stress and strain cannot be calculated from engineering stress and strain.However,true stress can still be d

49、efined as the force divided by the instantaneous area,provided the latter is taken as the minimum cross-sectional area.Some care must be taken when doing this,particularly at the later stages of neck development and at strains close to the fracture strain.A well-developed neck alters the stress stat

50、e in the neck region from that of simple tension.WordsNonuniform 不均匀Onset 开始 初始The effect is that T=F/Aneck becomes only an approximation.Additionally,internal voids,which are precursors to fracture,form in the last stages of a tensile test,and this leads to an underestimate of T when it is calculat