工程力学专业英语阅读.ppt

1、专业英语阅读,工程力学专业,Course Arrangement,Presentation,Start from 3rd class, 2 presentations each time Group work required 4-5 people in each group, 12 groups in total In each group, i.e. some responsible for the presentation, some responsible for answering questions Involvement from audience will earn extra

2、 credits Order of presentations could be volunteered or specified Reference rated,Presentation Flow,Introduce yourself Introduce your topic and the authors of the paper Name, university/institute, year published, journal published Provide an outline of the whole presentation One slide e.g. introduct

3、ion, experimental/simulation procedure, results, discussion, conclusion Background of the problem studied Methodology: how to study the problem Conclusions obtained,Sample Outline,Motivation Importance of cell adhesion Existing cell adhesion measurement techniques Laser-induced stress wave technique

4、 Experimental Setup Sample Preparation Experimental Results Observation of cell decohesion Quantitative adhesion measurement Conclusion and Discussion,Requirements,English speaking Chinese explanation Try to have more graphics than sentences on the slides Notes are allowed during the presentation,最多

5、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 主要基于文章的内容，可扩展，不可删减 可使用卡片，记录要点,Mechanics,Theoretical 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 Mechanic

6、s 量子力学,Mechanical Simulations: Solid, Fluid; BioMechanics; Soil Mechanics; Architectural Mechanics.,Topics,Engineering 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 Words,Units (单位)： Distance: k

7、ilo-meter (km), meter (m), milli-meter (mm), micro-meter (mm), nano-meter (nm), pico-meter (pm) inch, foot, mile Time: 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 centigr

8、ade (), Fahrenheit (F), Kelvin (K) Force: Newton (N), Stress: Pascal (Pa), mega-Pascal (MPa), giga-Pascal (GPa) bar, torr, atmosphere (atm) Strain,Prefix supersonic; superposition; supercomputer Method methodology Solid solidify Mechanics mechanical Biomechanics mechatronics mechanism mechanicalism

9、mechanicallyfoamed plastic,Example:,Mechanical Behavior of Materials,Mechanical Behavior of Materials, by Thomas H.Courtney Original edition published in 1990 in US Photocopies available in 2004 in China,Outline,Elastic deformation Permanent deformation The tension test Strain-rate sensitivity Yield

10、ing under multiaxial loading conditions Mohrs circle The hardness test The torsion test,Fracture Fracture toughness Tensile fracture Creep fracture Fatigue fracture Embrittlement Summary,Section 1.1 Introduction,This book deals with the mechanical behavior of solids, particularly as this behavior is

11、 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 material may fracture. Lesse

12、r 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: cooling rate 10/s,Al 5%-Cu

13、 alloy: cooling rate 1/s,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,While our aim is to relate the mechanical behavior of a solid to material structure at the microscop

14、ic 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 material microstru

15、cture and bulk properties that constitutes one of the most fruitful areas of materials science and engineering.,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 Deformation,When a solid is subjected to external forces, it und

16、ergoes 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 elastically; tha

17、t is, when the force is subsequently removed the body assumes the dimensions it had prior to its application.,The 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 dimensions.

18、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.,Some Important Words,Extension 伸长 external force 外力 Cross-sectional area 横截面积 Normal 法向，normal to垂直, perpen

19、dicular Parallel 平行,This 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 described. Linear elasticity of this

20、 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 extent of linear elasticity is usually

21、 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 is a measure of a materials bond stre

22、ngth.,Some Important Words,Normalize 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,A change in material shape can also be

23、 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 bond distortion within a solid

24、. 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.,Some Important Words,Shear 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 ex

25、hibit, 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 in a linear elastic solid

26、 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 stretched (the strain rate).

27、 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 initial application of th

28、e 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 sluggishly, recovered.,Some

29、Important Words,Viscoelasticity 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 which viscoelasticity is one example, need not be time-dependent. For example, nonlinear time-independent elasticity is observed in certain fine, strong

30、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 excess of this (whiskers are capable of such strains) the - relati

31、onship 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 (up to a thousand percent or so). This rubber elasticity is quit

32、e 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.,Some Important Words,Whisker 须晶 Elastomer 高弹性体，人造橡胶 Rubber 橡胶,Some Important Words,Fracture 断裂 Elastic deform

33、ation 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 Coupling 耦合 Microstructure 微观结构 Bulk properties 整体性质,Some Important Words,Normalize 归一化 Tensile modulus 拉伸模量；Youngs modul

34、us 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 Words,Shear stress 剪切应力 Shear strain 剪切应变 Relative displacement 相对位移 Position 位置,Some Important W

35、ords,Viscoelasticity 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 Words,Whisker 须晶 Elastomer 高弹性体，人造橡胶 Rubber 橡胶,Section 1.3 Permanent Deformation,A materials response to uniaxial loading is assessed most often by means of a tension test. F

36、orce 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, polycrystalline ceramics at room tempe

37、rature, and some metals and their alloys at low temperatures. Most metals at ordinary temperatures, and many ceramics at high temperatures, deform permanently before fracture.,36,s,o,y,k,e,elastic,yield,work harden,necking,T.S.,Some Important Words,Load cell 测压元件 Calibrate 标定 Extensometer 变形测定器; 张量计

38、 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, perpendicular Parallel 平行,Section 1.3 Permanent Deformation,39,s,o,y,k,e,elastic,yield,work harden,necking,T.S.,Some Important Words,Work hard

39、ening 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 by considering the total strain to result from a series of small, incremental extensions.,Express in differential form,In

40、tegrate from l0 to li,The constant-volume condition of plastic deformation allows relationships to be developed among stress and strain,For a tensile test For compression test, the relation will be opposite The difference between the true and engineering stresses and strains increases with plastic d

41、eformation. 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 with a geometrical instability, and not with a fundamental alteration in material behavior. Each and every tens

42、ile 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 the tensile

43、 point, the increase in flow stress,accompanying 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 rate of work

44、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 capacity h

45、as 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 be expressed quantitatively by realizing that at T.S. the engineering stress or equi

46、valently, the force reaches a maximum,Another 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 more of a mat

47、erial 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, provided the lat

48、ter 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.,Words,Nonuniform

49、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 calculated in the above way. By considering the neck as the deform

50、ing 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 they are not,

51、 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.,Words,Nonuniform 不均匀 Onset 开始 初始 Precursor 预示 Redefine 重新定义,A graph of true stress-true strain does not demonstrate anything

52、 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 effect, loc

53、alized 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. As discu

54、ssed in chapter 2, there is a fundamental basis-relating to chemical bond strength-that defines the form of this equation.,田承文,田承文,Words,Nonuniform 不均匀 Onset 开始 初始 Precursor 预示 Redefine 重新定义 Constitutive equation 本构公式,徐浩 王鹏,Words,Nonuniform 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,There 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 metal

56、s 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 plastici

57、ty 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 i

58、s characterized by a yield point.,徐浩 王鹏,徐浩 王鹏,徐浩 王鹏,Words,Nonuniform 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,Plastic flow commences at a stre

59、ss equal to the 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 up 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 l