材料科學(xué)與工程_專業(yè)英語_Unit_3_Structure-Property_Relationships_of_Materials譯文

1、Unit 3 Structure-Property Relationships of MaterialsTodays materials can be classified as metals and alloys, as polymers or plastics, as ceramics, or as composites; composites, most of which are man-made, actually are combinations of different materials.譯文：當(dāng)今的材料可以分為金屬和合金，聚合物或者塑料，陶瓷或復(fù)合材料；復(fù)合材料，它們大多數(shù)是人

2、造的，實際上是不同材料組合而成。Application of these materials depend on their properties; therefore, we need to know what properties are required by the application and to be able to relate those specification to the material. 譯文：這些材料的應(yīng)用取決于它們的性質(zhì)；因此，根據(jù)應(yīng)用的場合，我們需要知道什么樣的性質(zhì)是必需的，我們需要能夠把這些詳細(xì)說明同材料聯(lián)系起來。For example, a ladde

3、r must withstand a design load, the weight of a person using the ladder. However, the material property that can be measured is strength, which is affected by the load and design dimension. Strength values must therefore be applied to determined the ladder dimensions to ensure safe use. Therefore, i

4、n general, the structures of metallic materials have effects on their properties.譯文：比如，一個梯子必須能經(jīng)受住設(shè)計的載荷，也就是使用這個梯子的人的重量。然而，能夠測量的材料的性質(zhì)是強度，它為載荷和設(shè)計尺寸所影響。強度值因此被用來判定梯子的尺寸大小以保證安全使用。因此，通常說來，金屬材料的結(jié)構(gòu)對它們的性質(zhì)有影響。In a “tensile test” a sample is gradually elongated to failure and the tensile force required to elong

5、ate the sample is measured using a load cell throughout the test. The result is a plot of tensile force versus elongation.譯文：在一個張力測試實驗中，樣品緩慢地拉長直到失敗，并且拉長樣品所必需的拉力在整個測試過程中，用測壓元件測量。結(jié)果是拉力同伸長度之間的一個圖。結(jié)果是圖表。（有用的表示方法）The problem is that the load required to elongated the sample by a certain extent depends up

6、on the dimension of the sample. This would be a big problem if , for example, mechanical property data were to be used to design a bridge, since it is clearly impossible to test an entire bridge. Thus what is clearly needed is to make the data from the tensile test independent of the size of the sam

7、ple.譯文：問題是，拉伸樣品到一定程度所必需的載荷取決于樣品的尺寸。比如，如果機械性質(zhì)的數(shù)據(jù)被用于設(shè)計一座橋梁，既然測試整個橋梁是明顯不可能的，這樣，明顯需要的就是從與樣品尺寸無關(guān)的拉伸實驗中獲得數(shù)據(jù)。Thus, what is clearly needed is to make the data from the tensile test independent of the size of the sample. To achieve this end, we use “stress” and “strain”.The “true” stress( ) is defined as : ,

8、where F=force applied to the sample at any given instant and A= current cross-sectional area of the sample.譯文：這樣，明顯所需要的是從拉力測試實驗中得到和樣品尺寸無關(guān)的數(shù)據(jù)。為了達(dá)到這個目標(biāo)，我們使用“應(yīng)力”和“應(yīng)變”。真正的應(yīng)力（ ）可以這樣定義：這里F等于作用在樣品上任何一個給定時刻的拉力，A等于對應(yīng)當(dāng)時樣品的哼截面面積。The “true” strain( ) is defined as : ,where is the current gauge length and the or

9、igin gauge length of the sample.譯文：真正的應(yīng)力 被定義為 ，這里 是當(dāng)前測量長度， 是試樣的原始測量長度。True stress and true strain provide the most accurate description of what actually happens to the material during testing and so are widely used in materials science.  For engineering design, however, there are two problems.&

10、#160; 譯文：真正的應(yīng)力和真正的應(yīng)變提供材料在測試過程中所發(fā)生的最精確的描述，并且被廣泛使用在材料科學(xué)中。然而，對于工程設(shè)計來說，存在兩個問題。Firstly, true stress requires a knowledge of the value of A throughout the test, whereas in real world applications the designer of structures chooses an initial cross sectional area (A0).  Secondly true strain is not ver

11、y easy to visualize.  Consequently for engineering applications an “engineering” stress (s) and strain (e) are used in place of true stress and true strain:s = F / A0 and e = (l1 - l0) / l0 譯文：首先，真實應(yīng)力需要知道在整個測試過程中A的值，然而在實際應(yīng)用過程中，結(jié)構(gòu)設(shè)計者選擇初始橫截面面積A0。第二，真實拉力非常不容易看見。相應(yīng)的對于工程應(yīng)用來說，工程壓力（s）和拉力（e）被用來代替真實的應(yīng)力和

12、應(yīng)變： s = F / A0 和e = (l1 - l0) / l0 Stress has units of Pa (i.e. N m-2) and strain is dimensionless.  The concept of a stress is clearly closely related to that of pressure.  Using the definitions of stress and strain given above, the load versus elongation curve produced by the tensile tes

13、t can be converted into true stress - strain or engineering stress - strain curves.  Using these curves, it is now possible to describe the mechanical properties of metals and alloys.譯文：應(yīng)力有Pa的單位（比如N/m2），應(yīng)變是無量綱的。應(yīng)力的概念是明顯的同應(yīng)變十分相關(guān)的。用上面給出的壓力和拉力的定義，借助拉力試驗得到的載荷同伸長之間的曲線可以轉(zhuǎn)化為真實應(yīng)力應(yīng)變或者工程應(yīng)力應(yīng)變曲線。使用這些曲線，就可能

14、描述金屬和合金的機械性質(zhì)。In true and engineering stress-strain relationships for a “typical” metal, linear portion of the stress strain curves the material is deforming elastically at the Initial. 對一個典型的金屬來說，在真實和工程應(yīng)力應(yīng)變相互關(guān)系中，材料壓力曲線的線性部分是在最初的彈性形變In other words, if the load were removed the material will return to

15、 its initial, undeformed condition.  In the linear elastic region, the “stiffness” or “elastic modulus” is the amount of stress required to produce a given amount of strain.  For a tensile test, stiffness is described by Youngs modulus (E), which is given by:E = s / e or E = s / e換句話說，如果載荷

16、被除去，材料將返回到初始的，沒有形變的狀況。在線性彈性區(qū)域，“硬度”和“彈性模量”是產(chǎn)生一定量的應(yīng)力所必須的應(yīng)變。對一個拉伸測試，硬度借助Youngs 模量來描述，它由下面兩式來給出： E = s / e 或者 E = s / eThe greater the value of the stiffness, the more difficult it will be to produce elastic deformation.  Thus, for example, in selecting a material for the springs of a vehicle, stif

17、fness would be a key engineering design criterion.比較級比較級硬度值越大，產(chǎn)生彈性變形將越困難。比如，在選擇材料作為交通工具的彈簧時，硬度將是一個重要的工程設(shè)計標(biāo)準(zhǔn)。On exceeding a certain stress, known as the “yield stress” or “yield strength” (sy or sy in true and engineering stress respectively), the stress - strain curve ceases to be linear and the mat

18、erial begins to undergo permanent “plastic” deformation.  一旦超出某一種類應(yīng)力，大家知道為“屈服應(yīng)力”或者“屈服強度”（sy或者sy分別對應(yīng)于真實和工程應(yīng)力），應(yīng)力應(yīng)變曲線中止到線性部分，材料開始經(jīng)歷永久“塑性變形”。In the plastic region of the stress - strain curve, it is apparent that the stress required to continue plastic deformation is higher than that required to m

19、ake the material yield.  This phenomenon is called “work hardening” or “strain hardening”.  在應(yīng)力應(yīng)變曲線的塑性區(qū)域，顯然保持彈性形變所需的應(yīng)力比使材料屈服所需的應(yīng)力還要高。這個現(xiàn)象被稱作“機械硬化”或者“應(yīng)變硬化”。In the true stress - strain curve, it can be seen that work hardening actually continues right up until failure at the failure stress s

20、f.  In contrast the engineering stress - strain curve shows a maximum stress, the “ultimate ” (UTS), prior to final failure. 在真實的應(yīng)力應(yīng)變曲線中，可以看到 機械硬化實際上往右向上增加直到斷裂應(yīng)力sf時才斷裂。相反，工程應(yīng)力應(yīng)變曲線顯示在材料最后斷裂之前，有一個最大應(yīng)力，也就是“最終的”拉應(yīng)力，During final failure, the sample starts to “neck” down to failure and this is n

21、ot accounted for when A0, rather than A, is used to calculate a stress.  Nonetheless, for a design engineer, the UTS is a very useful datum and the UTS (rather than sf) is normally used as the measure of the “tensile strength” of a material.在最終斷裂時，樣品開始下滑止到斷裂，并且這不是說明當(dāng)A0，優(yōu)于A，被用來計算應(yīng)力時。但是，對于一個設(shè)計工程師

22、來說，UTS是一個非常有用的數(shù)據(jù)，UTS（優(yōu)于sf）通常被用來測量材料的抗拉強度?！癉uctile” materials are those that can undergo plastic deformation and so the greater the extent of plastic deformation, the higher the “ductility”.  The engineering strain to failure is a common measure of ductility.  Note: if l1 is measured after

23、the sample has failed, then the elastic portion of the samples elongation will be removed, since the applied load is removed when the sample fails.  Thus only plastic deformation and not elastic deformation will contribute to an l1 measured after failure.延展材料是那些能夠經(jīng)受塑性形變的材料，并且塑性形變量越大，延展性越大。工程應(yīng)力到

24、斷裂是一個普通的延展性的測量。標(biāo)記：如果當(dāng)試樣斷裂以后，l1被測量，然后試樣延長的彈性部分將被除去，當(dāng)試樣斷裂時應(yīng)用載荷被除去。當(dāng)材料斷裂以后，這樣僅僅只有塑性形變和非塑性形變將對測量的l1有貢獻(xiàn)。The “hardness” of a material is a measure of the resistance to plastic deformation.  Hardness is measured by determining the depth or projected area of an indentation produced by a standard indent

25、or (these can be e.g. tool steel balls or diamonds in the shape of an inverted pyramid, depending on the technique used).  材料的“硬度”是阻礙彈性形變的一個量度。硬度通過測定由標(biāo)準(zhǔn)壓針產(chǎn)生的凹槽的深度或者投影面積來測量（這些可以是比如鋼球或者漏斗形的鉆石，取決于使用的技術(shù)）。The higher the hardness of the material, the shallower the indentation for a given load and the

26、 smaller the projected area.  Hardness is an important property in many applications.  Consider, as an example, a material intended to serve as the liner for a bearing supporting a rotating shaft.  Many bearing alloys consist of a hard phase in a soft phase.  The purpose of the h

27、ard phase is to resist abrasion as the shaft turns.  The soft phase serves both to bind the hard phase into place and allows wear debris to become embedded, thus preventing the debris from damaging the shaft. 材料的硬度越高，對于一定的載荷凹槽的深度越淺并且凹陷面積越小。硬度在許多應(yīng)用中是一個重要性質(zhì)。作為一個例子，考慮一種目的是用作軸瓦，用作旋轉(zhuǎn)軸的支撐體材料。許多軸承合金由在

28、軟相中的硬相組成。硬相的目的是耐磨損當(dāng)軸轉(zhuǎn)動的時候。軟相起把硬相鑲嵌在其中的場所，并且允許磨損的碎片進(jìn)入軟相，這樣阻止碎片損壞軸。The “toughness” of a material is a measure of how much energy can be absorbed by the material before failure.  Toughness is determined by subjecting the material to an impact from a swinging hammer and measuring the amount of ener

29、gy absorbed from the swing (the less energy is absorbed, the higher the hammer will swing after fracturing the sample).  材料的“韌度”是材料在斷裂之前能夠吸收多少能量的量度。韌度這樣測量：材料受到一個擺動的鐵錘的沖擊后，測量從擺動的中吸收的能量來測量。（能量吸收的越少，破壞試樣以后鐵錘將擺動的越高）Energy is absorbed by plastic deformation and hence ductile materials show a high to

30、ughness.  In contrast, brittle materials can have a high strength, but have negligible toughness.  For example, it is preferable for the crumple zones in your car to absorb as much of an impact as possible through extensive plastic deformation (even if this totals the car!) than to have yo

31、ur bones undergo brittle failure.  能量被塑性形變吸收，因此延展性材料顯示一個很高的韌性。相反，脆性材料能有高的強度，但是有少量的硬度。比如，對在你汽車?yán)锏囊粋€褶皺區(qū)域來說，比起使你的骨骼遭受脆性的斷裂，通過大規(guī)模的塑性形變盡可能多的吸收沖擊是可取的（盡管這個占據(jù)整個汽車?。㎜ikewise, a concrete guard rail is good for protecting construction workers, because the kinetic energy of an oncoming vehicle is absorbed b

32、y deformation of the vehicle (which can be tough luck on the occupants of the vehicle if the impact exceeds the energy absorbing capability of the crumple zones in the car!).  同樣，一個混凝土的保護(hù)欄對保護(hù)建筑工人是有益的，因為一輛臨近的交通工具的動能被交通工具的形變所吸收（如果這個沖擊超出汽車?yán)锩骜薨檯^(qū)域的吸收能量容量，這對于交通工具的主人來說，可能是一個噩耗）。In contrast, a steel gu

33、ard rail protects drivers because plastic deformation of this absorbs energy efficiently in the event of an impact (but is not so good at protecting construction workers because the vehicle is not brought to a sudden halt).  So do what the signs say and slow down for construction!相反，一個鋼的保護(hù)欄保護(hù)司機

34、，因為在沖擊出現(xiàn)時，這些鋼的保護(hù)欄的塑性形變有效的吸收能量（但是不擅長保護(hù)建筑工人因為使用這種材料，交通工具是不能帶來一個緊急的停止）。因此按照標(biāo)志所說的做，對建筑來說可以減慢。In addition to the properties discussed above, other mechanical properties are very important.  These include resistance to “fatigue” failure due to cyclic loading and to thermally assisted, time-dependent

35、“creep” deformation and failure.  除了上面談?wù)摰降男再|(zhì)以外，其他力學(xué)性能是非常重要的。這些力學(xué)性質(zhì)包括由于循環(huán)的載荷產(chǎn)生的抗疲勞斷裂，和熱助的，時間有關(guān)的蠕性形變和斷裂。There are many possible examples of the relationship between processing, structure and properties.  However, the following example is chosen because it illustrates a number of the features

36、 discussed in material science.有許多加工、結(jié)構(gòu)和性能之間聯(lián)系的例子。然而，下面的例子被選擇是因為它被用來舉例說明許多材料科學(xué)中討論的特征。Nickel - boron alloys form the basis of brazes used to join many nickel-base alloys, especially in aerospace.  An eutectic forms between nickel and the nickel boride Ni3B and so a nickel-boron braze can melt an

37、d flow without melting the nickel-base materials to be joined.  鎳-硼合金形成青銅的基底，這些青銅被用來聯(lián)接許多基于鎳的合金，尤其是在航空和航天領(lǐng)域。一個共晶形成位于鎳和鎳化硼Ni3B之間，因此沒有基于鎳的材料加入進(jìn)去，鎳硼釬焊可以熔化并流動。However, boron diffuses as an interstitial in nickel and can diffuse rapidly away into the substrates.  Dispersing the boron removes the

38、 liquid (which was only there because, by forming an eutectic, boron depresses the melting-point of nickel) and this allows components to operate at high temperatures without these melting in service.  然而，硼在鎳中間擴散并且能夠快速的擴散進(jìn)底金屬。把硼分散開來除去液體（僅僅只有只是在那里，通過形成共晶，因為硼壓低了鎳的熔點），這允許零件在高溫下操作不會在使用過程中產(chǎn)生熔化現(xiàn)象。A p

39、roblem with using boron-containing brazes is that Ni3B is very brittle and this means that these brazes can not be produced as a sheet by conventional means, such as rolling.  Thus, these types of brazes are often used as a powder which is inconvenient to handle and oxide from the surface of the powder particles can reduce the strength of joints.  As an alternative, a molten nickel - boron alloy can be sprayed onto the surface of a rapidly spinning copper wheel, which carries h