【正文】 e curve. At T the specimen breaks, and this load is called the breaking load. The value of the maximum load S divided by the original crosssectional area of the specimen is referred to as the ultimate tensile strength of the metal or simply the tensile strength.Logically speaking, once the 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. Two reasons can be given for this behavior:1. the strain hardening of the material。mini?i?]adj. 逐漸縮小的；衰減的v. 減少；遞減；衰減；削弱的權(quán)勢 crosssectional area of the specimen, suffered on account of 1. On account of the weather, we had to cancel the projected outing.the plastic deformation.The more plastic deformation the metal undergoes, the harder it bees, due to workhardening. The more the metal gets elongated the more its diameter(and hence, crosssectional area) is decreased. This continues until the point S is reached.After S, the rate at which the redution in area takes place, exceeds the rate at which the stress increases. Strain bees so high that the redution in area begins to produce a localized effect at some point. This is called neching.Reduction in crosssectional area takes place very rapidly。 and are the original and the final crosssectional area. 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。化學(xué)特性 許多化學(xué)特性都?xì)w入到這個范疇。而在這其中最重要的是耐腐蝕性，通俗的解釋是材料在特定大氣中長期使用時，抵抗腐蝕的能力。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。材料在加載時，隨著載荷大小的變化，尺寸會發(fā)生改變。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。 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。在曲線的實際繪制中，比例極限值要稍微比彈性極限值低。這種現(xiàn)象在一些有色金屬中常常出現(xiàn)。實際上依靠測試儀器的精確性可以使比例極限和彈性極限區(qū)分得更清晰。同時，試件發(fā)生加工硬化。這一點叫做屈服極限點。屈服應(yīng)力叫做屈服極限。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。最大荷載值S除以試件的橫截面積為金屬的最大拉伸強度或簡單地稱為拉伸強度。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。 （For Christ was God, and suffered on account of us, being himself the Father, that he might be able to save ，為我們受苦，他自己身為父，好叫祂也能救贖我們。金屬拉伸越長它的直徑越小。 超過S點后，面積減少的速度超過了應(yīng)力增加的速度。叫做頸縮。 伸長率和面積減少率表示了材料的延展性。 cylindrical and conical sections。 .回轉(zhuǎn)殼是由一條直線或曲線繞著一根軸旋轉(zhuǎn)形成的曲面（回轉(zhuǎn)體是由一個面繞著一軸旋轉(zhuǎn)而成的）。 supporting loads without significant bending or shear stresses。The analysis of the membrane stresses induced in shells of revolution by internal pressure gives a basis for determining the minimum wall thickness required for vessel shells. The actual thickness required will also depend on the stresses arising from the other loads to which the vessel is subjected.對受內(nèi)壓回轉(zhuǎn)體的薄膜應(yīng)力分析為確定容器殼體最小壁厚奠定了基礎(chǔ)。Consider the shell of revolution of general shape shown in under a loading that is rotationally symmetric。Let P=pressure, 令：P=壓力 t=thickness of shell, t=壁厚 =the meridional (longitudinal) stress, the stress acting along a meridian, =經(jīng)向應(yīng)力 =the circumferential or tangential stress, the stress acting along parallel circles (often called the hoop stress), =周向應(yīng)力 =the meridional radius of curvature,r1=經(jīng)向曲率半徑 =circumferential radius of =環(huán)向曲率半徑Note: the vessel has a double curvature。Consider the forces acting on the element defined by the points a. b c, d. Then the normal ponent (ponent acting at right angels to the surface) of the force on the element 假設(shè)作用在元件上的力由a、b、c、d四點確定。Cylinder()圓柱體（）A cylinder is swpet out by the rotation of a line parallel to the axis of revolution, so:圓柱體是由一條平行于軸的直線繞著軸旋轉(zhuǎn)形成的，于是：where D is the cylinder 。Substitution in equations () and () gives: 代入方程（）和（）得： ()The maximum values will occur at 。 (Select from: , Chemical Engineering, , and Edition, Pergamon Press,1996.) Word and Expressions1. membrane n. 薄膜，隔膜，隔板2. revolution n. 回轉(zhuǎn)，旋轉(zhuǎn)（運動）3. cylindrical （體型）的，（圓）圓筒的4. conical ，橢球的5. hemispherical （形，狀）6. ellipsoidal ，橢球的7. torispherical 8. include ，導(dǎo)致，誘發(fā)9. symmetric ，勻稱的，平均的10. curvature ，曲率11. resist ，耐（得?。?2. equate ，使等于13. meridional ，經(jīng)向的14. substitution Metals金屬About threequarters of the elements available can be classified as metals, and about half of these are of at least some industrial or mercial importance. Although the word metal, by strict definition, is limited to the pure metal elements, mon usage gives it wider scope to include metal alloys. While pure metallic elements have a broad range of properties, they are quite limited in mercial use. Metal alloys, which are binations of two or more elements, are far more versatile and for this reason are the form in which most metals are used by industry. 大約現(xiàn)有元素中的四分之三可歸類為金屬；而大約一半金屬元素都有一定的工業(yè)或商業(yè)上的重要性。盡管純金屬有很多特性，他們在商業(yè)中的應(yīng)用也很局限。 Metallic materials are crystalline solids. Individual crystals are posed of unit cells repeated in a regular pattern to form a threedimensional crystallattice structure. A piece of metal is an aggregate of many thousands of interlocking crystals (grains) immersed in a cloud of negative valence electrons detached from the crystals’ atoms. These loose electrons serve to hold the crystal structures together because of their electrostatic attraction to the positively charged metal atoms (ions). The bonding forces, being large because of the closepacked nature of metallic crystal structures, account for the generally good mechanical properties of metals. Also, the electron cloud makes most metals good conductors of heat and electricity. 金屬材料是晶狀固體。一塊金屬則是成千上萬相聯(lián)晶體的集合體，而這些晶粒都沉浸在從晶體原子中脫離出來的帶負(fù)電的價電子云中。而由于金屬結(jié)晶結(jié)構(gòu)致密本質(zhì)導(dǎo)致的這種很大的結(jié)合力是造成金屬一般都具有良好機械性質(zhì)的原因。 Metals are often identified by the method used to produce the forms in which they are used. When a metal has been formed or shaped in the solid, plastic state, it is referred to as a wrought metal. Metal shapes that have been produced by pouring liquid metal into a mold are referred to as cast metals. 在大多數(shù)情況下，根據(jù)生產(chǎn)金屬的模板來辨認(rèn)金屬。將液體金屬傾倒入模型形成的金屬稱為澆鑄金屬。所有黑色金屬的基本成分都是鐵元素。 Except for mercially pure iron, all ferrous materials, both irons and steels, are considered to be primarily ironscarbon alloy systems. Although the carbon content is small (less th