工程力学专业英语阅读

1、专业英语阅读工程力学专业1Course Arrangement2PresentationStart 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 credi

2、ts Order of presentations could be volunteered or specifiedReference rated3Presentation 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, experime

3、ntal/simulation procedure, results, discussion, conclusionBackground of the problem studiedMethodology: how to study the problemConclusions obtained4Sample OutlineMotivationImportance of cell adhesion Existing cell adhesion measurement techniquesLaser-induced stress wave techniqueExperimental SetupS

4、ample PreparationExperimental ResultsObservation of cell decohesion Quantitative adhesion measurementConclusion and Discussion5RequirementsEnglish speakingChinese explanation Try to have more graphics than sentences on the slidesNotes are allowed during the presentation6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，

5、要通过自己讲解主要基于文章的内容，可扩展，不可删减可使用卡片，记录要点7MechanicsTheoretical 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Mechanical Simulations: Solid, Fl

6、uid; BioMechanics; Soil Mechanics; Architectural Mechanics.8TopicsEngineering 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9Frequently Used WordsUnits (单位)：Distance: kilo-meter (km), meter (m), milli-meter (mm), mic

7、ro-meter (mm), nano-meter (nm), pico-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 (

8、N), Stress: Pascal (Pa), mega-Pascal (MPa), giga-Pascal (GPa) bar, torr, atmosphere (atm)Strain10Prefix & Suffixdiffer different difference differentiateconduct conductivity superconductivity; supersonic; superposition; supercomputer Method methodologySolid solidifyMechanics mechanical Biomechanics

9、mechatronics mechanism mechanicalism mechanicallyfoamed plastic11Example:Mechanical Behavior of Materials12Mechanical Behavior of Materials, by Thomas H.CourtneyOriginal edition published in 1990 in USPhotocopies available in 2004 in China13OutlineElastic deformationPermanent deformationThe tension

10、testStrain-rate sensitivityYielding under multiaxial loading conditionsMohrs circleThe hardness testThe torsion testFractureFracture toughnessTensile fractureCreep fractureFatigue fractureEmbrittlementSummary14Section 1.1 IntroductionThis book deals with the mechanical behavior of solids, particular

11、ly as this behavior is affected by processes taking place at the microscopic and/or atomic level. 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 materi

12、al may fracture. Lesser values of force may result in material permanent deformation without fracture 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.Al 5%-Cu alloy: cooli

13、ng rate 10/sAl 5%-Cu alloy: cooling rate 1/s15Some 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16While our aim is to relate the mechanical behavior of a solid to material structure at

14、 the microscopic and atomic level, this response is manifested macroscopically. Thus, to fulfill adequately the objective 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 mate

15、rial microstructure and bulk properties that constitutes one of the most fruitful areas of materials science and engineering.17Some Important Words Macroscopic 宏观 microscopic 微观Coupling 耦合Microstructure 微观结构Bulk properties 整体性质18Section 1.2 Elastic DeformationWhen a solid is subjected to external fo

16、rces, it undergoes a change in shape. When the load is released, the shape may not returned to what is was prior to the application 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 elas

17、tically; that is, when the force is subsequently removed the body assumes the dimensions it had prior to its application. 19The elastic behavior 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

18、dimensions. For example, doubling of initial sample length leads to a doubling of the extension, whereas if the sample cross-sectional area normal to the applied force is doubled, the extension is halved.l+DlFFFFF2l+2Dll+Dl/2FAA2A20Some Important Words Extension 伸长 external force 外力Cross-sectional a

19、rea 横截面积Normal 法向，normal to垂直, perpendicularParallel 平行21This equation is often written in normalized form of stress and strain, with E the 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

20、 described.Linear elasticity of this kind is observed in all classes of solids. It is the dominant mode of elastic deformation in all solids at low temperatures, in crystalline solids and inorganic glasses up to moderately high temperatures, and in noncrystalline polymers at low temperatures. The ex

21、tent of linear elasticity is usually quite limited; that is, most materials are capable of being linearly elastically extended only to strains on the order of several tenths of a percent. Linear elasticity represents the stretching (or compression/distortion) of atomic bonds, and for this reason E i

22、s a measure of a materials bond strength.22Some 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23A change

23、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 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 bo

24、nd 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 from “bending” of atomic bonds.24Some Important WordsShear stress 剪切应力Shear strain 剪切应变Relative displacement 相对位移Position 位置25Almost all

25、 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 noncrystalline polymers, but also occurs to a much more limited extent in crystalline solids and inorganic glasses. The strain

26、 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 of loading. Moreover, the level of stress attained depends, too, on the rate at which a viscoelastic material is st

27、retched (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 manifested by a strain that varies with time under conditions of a constant applied stress. That is, upon

28、 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 removal of the load, the linear elastic strain is instantaneously, and the viscoelastic strain sl

29、uggishly, recovered.loadingunloadingloadingunloadinge1s1e1s126Some 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27Nonlinear elasticity, of which viscoelasticity is one example, need not be time-dependent. For example, nonlinear

30、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 elastic way up to strains on the order of half a percent. For elastic strains in ex

31、cess 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 temperature range are capable of demonstrating extensive elastic strains

32、(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 of linear elasticity. 28Some Important WordsWhisker 须晶Elastomer 高弹性

33、体，人造橡胶Rubber 橡胶29Some 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30Some Important Words Macroscopic 宏观 microscopic 微观Coupling 耦合Microstructure 微观结构Bulk properties 整体性质31Some Importan

34、t 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32Some Important WordsShear stress 剪切应力Shear strain 剪切应变Relative di

35、splacement 相对位移Position 位置33Some 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34Some Important WordsWhisker 须晶Elastomer 高弹性体，人造橡胶Rubber 橡胶35Section 1.3 Permanent DeformationA materials response to uniaxial loading is assessed mo

36、st 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. Examples include inorganic glasses, po

37、lycrystalline 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.36Some Important WordsLoad cell 测压元件Calibrate 标

38、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37Some 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38Section 1.3 Permanent Deformation39soykeelastic yield work hardenneckingT.S.39Some Important Wor

39、dsWork hardening 应变强化True stress 真实应力Engineering stress 工程应力40Engineering strain by definition is overestimated.True strain is based on instantaneous sample length. It can be approximated by considering the total strain to result from a series of small, incremental extensions. 41Express in different

40、ial form Integrate from l0 to liThe constant-volume condition of plastic deformation allows relationships to be developed among stress and strain42For a tensile testFor compression test, the relation will be oppositeThe difference between the true and engineering stresses and strains increases with

41、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.43The tensile point is associated with a geometrical instability, and not with a fundamental alteration in material behavior.Each and e

42、very 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 these regions, and this leads to a locally greater reduction in area. For strains less than th

43、e tensile point, the increase in flow stress44accompanying the greater strains is large enough to lead to removal of the incipient instability. This process occurs regularly and repeatedly during tensile loading, and could be monitored if sufficiently accurate instrumentation were available. The rat

44、e 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 instability sufficiently to remove it. As the tensile point, the work-hardening

45、capacity has been diminished enough that an instability once formed continues to develop.45The criterion for necking is related to the materials work hardening tendencies v.s. those that initiate instability. The criterion can be expressed quantitatively by realizing that at T.S. the engineering str

46、ess or equivalently, the force reaches a maximum46Another 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 fracture. Since %R.A. is independent of sample gage length, it is m

47、ore 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 defined as the force divided by the instantaneous area, provi

48、ded 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 state in the neck region from that of simple tension.47Words

49、Nonuniform 不均匀Onset 开始 初始48The 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 calculated in the above way.By considering the neck as

50、the deforming volume, true strain can also be redefined following necking. Before necking, T=ln(li/l0) (or equivalently, T=ln(Ai/A0) ). Following necking, it is defined only on an area basis, that is, by the latter expression with Ai taken as the neck area. Because confusion often arises as when the

51、y are not, Table 1.1 synopsizes engineering an true definitions of stress and strain, and expression for them appropriate to tensile flow before and after necking are also listed there.49WordsNonuniform 不均匀Onset 开始 初始Precursor 预示Redefine 重新定义50A graph of true stress-true strain does not demonstrate

52、anything unusual at tensile strength (Fig. 1.9). This is additional evidence that necking is geometric in origin and does not reflect changes in material properties. One final point is in order. We have mentioned that, prior to necking, TE. At some strain greater than E, this is no longer so. In eff

53、ect, localized deformation leads to E values that are no indication of the much greater strain found in the neck region; true strain, as calculated by ln(A0/Aneck), is not subject to such a shortcoming.=/E is a constitutive equation relating strain and stress during linear elastic tensile loading. A

54、s discussed in chapter 2, there is a fundamental basis-relating to chemical bond strength-that defines the form of this equation.田承文51田承文52WordsNonuniform 不均匀Onset 开始 初始Precursor 预示Redefine 重新定义Constitutive equation 本构公式53徐浩 王鹏54WordsNonuniform 不均匀Onset 开始 初始Precursor 预示Redefine 重新定义Constitutive equ

55、ation 本构公式Diversity 多样性Empirical equation 经验公式Coefficient 参数55There is no physical significance, per se, to K; it can be thought of simply as the true stress required to cause a true strain of unity. On the other hand, and as expected, n correlates with a materials resistance to necking. For metals

56、at ordinary temperatures, n is in the range from ca. 0.02 to about 0.50.The stress-strain curve of Fig. 1.6a accurately schematizes the behavior of many engineering solids, particularly metals at temperatures at which they exhibit time-independent plastic flow. However, the initiation of plasticity

57、in certain solids (including some metals, polymers, and ceramics and depending on temperature, strain rate and structural considerations) does not follow the scenario of Fig. 1.6. instead these materials exhibit a yield point. The room temperature engineering stress-strain curve of a mild steel is c

58、haracterized by a yield point.徐浩 王鹏56徐浩 王鹏57徐浩 王鹏58WordsNonuniform 不均匀Onset 开始 初始Precursor 预示Redefine 重新定义Constitutive equation 本构公式Diversity 多样性Empirical equation 经验公式Coefficient 参数Per se 本身 本质上Correlate 相关 关联ca. Circa 大约Schematize 图式化，计划Mild steel 低碳钢59Plastic flow commences at a stress equal to t

59、he upper yield point (UYP), and then continues at a lower stress level (LYP, the lower yield point). We see that for this steel, as well as for other materials manifesting a yield point, the stress required to initiate plastic flow is greater than that required to continue it. This situation holds u

60、p to a certain strain (for steel this strain is the Luders strain noted in Fig. 1.10). Plastic deformation is heterogeneously distributed along the gage length of the steel during this initial stage of plastic deformation. A small permanently deformed volume first forms at the UYP and spreads along