機械設(shè)計制造及其自動化專業(yè)英語_Unit 03 Mechanical Properties of Materials

1、word alkalinity n. 堿性；堿度 lkliniti tensile a. 受拉的；拉伸的 tensail compression n. 壓縮；壓力 kmpren shear n. 剪切；切應(yīng)變 i torsion n. 扭轉(zhuǎn)；轉(zhuǎn)矩 t:rn impact n. 沖擊；沖力；影響 mpkt fatigue n. 疲勞 fti: creep n. 蠕變 kri:p specimen n. 試件；試樣 spesiminMechanical Properties of Materials1word cross-section 橫截面 ordinate n. 縱坐標 :rdineit a

2、bscissa n. 橫坐標 bsis deviation n. 偏離；偏移 di:viein time-lag 延時；落后；時滯 yield n. ； v. 屈服 ji:ld elongation n. 延伸率；伸長 i:lein diminish n. 減?。豢s小 dimini necking n. 頸縮；形成細頸現(xiàn)象 nekiMechanical Properties of Materials2Mechanical Properties of Materials The material properties can be classified into three major head

3、ings: (i) Physical, (ii) Chemical, (iii) Mechanical. Physical propertiesDensity or specific gravity, moisture mst content, etc., can be classified under this category ktg:ri. 材料特性主要分為三類：(i)物理特性，(ii)化學(xué)特性，(iii)力學(xué)性能。 物理特性密度或特定的重力，濕(氣)度等都屬于此范疇。3Chemical properties Many chemical properties come under thi

4、s category. These include acidity sdti or alkalinity lkliniti, reactivity and corrosion. 許多化學(xué)特性都歸入到這個范疇。其中包括酸性或堿性，活性和腐蝕性。4Chemical properties The most important of these is corrosion which can be explained in laymans lemn terms as the resistance of the material to decay dke while in continuous use i

5、n a particular atmosphere. 而在這其中最重要的是腐蝕性，通俗的解釋是材料在特定大氣中長期使用時，抵抗腐(敗)蝕的能力。5Mechanical properties Mechanical properties include the strength properties like tensile, compression, shear, torsion, impact, fatigue and creep . 力學(xué)特性包括諸如拉伸，壓縮，剪切，扭轉(zhuǎn)，沖擊，疲勞和蠕變等強度特性。6Mechanical properties The tensile strength of

6、 a material is obtained by dividing the maximum load, which the specimen bears by the area of cross-section of the specimen. 一種材料的拉伸強度由試件承載的最大載荷除以試件的橫截面積得到。7Mechanical properties This is a curve plotted between the stress along the Y-axis(ordinate) and the strain along the X-axis(abscissa ) in a ten

7、sile test. 如圖所示為在拉伸試驗中沿著X軸（橫軸）的應(yīng)變和沿著Y軸（縱軸）的應(yīng)力之間的關(guān)系曲線。8Mechanical properties A material tends to change or changes its dimensions when it is loaded, depending upon the magnitude of the load. 材料在加載時，隨著載荷大小的變化，尺寸會發(fā)生改變。9Mechanical properties When the load is removed it can be seen that the deformation d

8、isappears. For many materials this occurs up to a certain value of the stress called the elastic limit e. 當(dāng)卸載時，變形消失。對于許多材料來說，上述情況發(fā)生的應(yīng)力極限值稱為彈性極限e 。10Mechanical properties This is depicted dipekt by the straight line relationship and a small deviation divien thereafter, in the stress-strain curve (Fig

9、. 3. 1). 在應(yīng)力-應(yīng)變曲線描述中，直線關(guān)系和隨后的小小的彎曲(偏離)描述了上述的加載和卸載(如圖3.1)。11Mechanical propertiescurve12Mechanical properties Within the elastic range, the limiting value of the stress up to which the stress and strain are proportional, is called the limit of proportionality. 在彈性范圍內(nèi)，應(yīng)力應(yīng)變成比例的應(yīng)力極限值稱為比例極限。13Mechanical

10、properties In this region, the metal obeys Hookes law, which states that the stress is proportional to strain in the elastic range of loading (the material completely regains its original dimensions after the load is removed). 在這個區(qū)域中，金屬遵守胡克定律闡述了在加載的彈性范圍內(nèi)，應(yīng)力和應(yīng)變成比例關(guān)系（材料在卸載后，能夠完全回復(fù)它原來的尺寸）。14Mechanical

11、properties In the actual plotting of the curve, the proportionality limit is obtained at a slightly lower value of the load than the elastic limit. 在曲線的實際繪制中，比例極限值要稍微比彈性極限值低。15Mechanical properties This may be attributed to the time-lag in the regaining of the original dimensions of the material. Th

12、is effect is very frequently noticed in some no-ferrous metals. 這可能是由于材料回復(fù)原尺寸需要的時間延遲。這種現(xiàn)象在一些有色金屬中常常出現(xiàn)。 ferrous frs 含鐵的 ferrous metal 黑色金屬16Mechanical properties While iron and nickel exhibit clear ranges of elasticity, copper, zinc, tin, etc, are found to be imperfectly elastic even at relatively lo

13、w values of stresses. 鐵和鎳存在明顯的彈性范圍，銅，鋅，錫等即使在相當(dāng)?shù)偷膽?yīng)力值下彈性也表現(xiàn)得不是很完美地。17Mechanical properties Actually the elastic limit is distinguishable from the proportionality limit more clearly depending upon the sensitivity of the measuring instrument. 實際上依靠測試儀器的敏感性可以使比例極限和彈性極限區(qū)分得更清晰。18Mechanical properties When

14、the load is increased beyond the elastic limit, plastic deformation starts. Simultaneously the specimen gets work-hardened. 當(dāng)在彈性極限之上增大載荷時會產(chǎn)生塑性變形。同時，試件發(fā)生加工硬化。19Mechanical properties A point is reached when the deformation starts to occur more rapidly than the increasing load. This point is called the

15、 yield point Q. 到達某點后變形的速度快于載荷增加的速度。這一點叫做屈服極限點Q。20Mechanical properties The metal which was resisting the load till then, starts to deform somewhat rapidly, i. e. , yield. The yield stress is called yield limit y. 一開始一直在抵抗載荷的金屬在這一點后開始迅速地發(fā)生形變，也就是，屈服。屈服應(yīng)力叫做屈服極限y 。21Mechanical properties The elongation

16、 of the specimen continues form Q to S and then to T. The stress-strain relation in this plastic flow period is indicated by the portion QRST of the curve. At T the specimen breaks, and this load is called the breaking load. 試件從Q到S在到T不斷地延長。在這個塑性流動期間的應(yīng)力-應(yīng)變關(guān)系表示為曲線上的QRST段。在T點試件斷裂，此時的載荷稱為斷裂載荷。22Mechanic

17、al properties The value of the maximum load S divided by the original cross-sectional area of the specimen is referred to as the ultimate ltmit tensile strength of the metal or simply the tensile strength u. 最大荷載值S除以試件的橫截面積為金屬的極限(最大)拉伸強度或簡單地稱為拉伸強度u 。23Mechanical properties Logically speaking, once t

18、he elastic limit is exceeded, the metal should starts to yield, and finally break, without any increase in the value of stress. But the curve records an increased stress even after the elastic limit is exceeded. 邏輯上來說，一旦超過彈性極限，金屬應(yīng)該就會屈服直至最后斷裂，在應(yīng)力值上應(yīng)該沒有增加。但是實際的曲線卻記錄了在超過彈性極限后的增加了的應(yīng)力。24Mechanical proper

19、ties Two reasons can be given for this behavior:(1) the strain hardening of the material;(2) the diminishing cross-sectional area of the specimen, suffered on account of the plastic deformation. 這種現(xiàn)象的發(fā)生可能有兩種原因：(1) 材料的應(yīng)變強化；(2) 由于塑性變形引起的試件橫截面積的縮小。25Mechanical properties The more plastic deformation th

20、e metal undergoes, the harder it becomes, due to work-hardening. The more the metal gets elongated the more its diameter (and hence, cross-sectional area) is decreased. This continues until the point S is reached. 由于加工硬化，金屬在發(fā)生塑性變形時會變得越來越硬。金屬拉伸越長它的直徑越小。這種現(xiàn)象一直持續(xù)到曲線上的S點。26Mechanical properties After S, the rate at which the reduction in area takes place, exceeds the rate at which the stress increases. Strain becomes so high that the reduction in area begins to produce a localized effect at s