材料5
旋转体的静态和动态平衡
单个圆盘在它的两个平行刀刃的车轴上旋转可以检测到圆盘失去平衡，如图1.22所示。圆盘会旋转最终会偏停在重的一面。这类的不平衡称为静态平衡，因为它能够通过静力学的方法检测。
通常，一般的转子都会安装在前轴上，例如电动机电枢或者汽车发动机机轴。一个类似上述的测试表明，这种零件处在静态平衡，但是当系统旋转起来后就表现出不平衡了。 举例，考虑带两个圆盘的轴，如图1.23。如果两个不等重的圆盘处于平衡，质心位于轴的两侧且两质心成180°，系统会沿轴处于静态平衡。然而，当系统旋转，不平衡的圆盘将会受到旋转离心力会摇晃轴承上的轴。因为这种不平衡的类型我们称作动态失衡。
图1.24展示了一个一般情况下地动态和静态失衡。通过在旋转的任意两平行面增加正确的重量不平衡力P和Q能够被消除。
首先考虑失衡力P,它能够被两个平行的力Q *c/l 和 Q *d/l代替。类似的，Q可以被Q *c/l 和 Q *d/l代替。这两个不同平面的力可以合为单个的合力就可以被单个的校正重量平衡如所展示。两个校正重量C1和C2用以平衡P和Q，系统式静态和动态平衡。着重强调动态平衡体系也是静态平衡的。相反，静态平衡体系就是动态平衡体系就不一定是正确的。 举例 一个4英寸的转子在距离最左边一英寸的一个平面上有3盎司的重量，在中心面上有2盎司的重量，从左边看去第一个不平衡点顺时针方向两者成90°。校正重量分别在两个端面上，角度处于两不平衡点的角度里
解答 3盎司不平衡重量相当于左边平面2.24盎司的重量和右边的0.75盎司的重量，如图1.25所示。中部2盎司的重量显然等于两端1盎司的重量之和。 分别合成两端的不平衡量，得校正量：
左端：
cθ1??12?(2.25)12.25?2?2.47 盎司
ο'1tan34?1240 第一个不平衡点的顺时针方向
右端：
2cθ
2?()?1?1?1.252 盎司
2?tan10.75?53? 第一个不平衡点的逆时针方向
(摘自：William T. Thomoson, 《振动理论及应用》普伦蒂斯霍尔公司 ,1965.）
Reading Material 6
Stainless steel
Stainless steels do not rust in the atmosphere as most other steels do. The term “stainless” implies a resistance to staining, rusting, and pitting in the air, moist and polluted as it is, and generally defines a chromium content in excess of 11% but less than 30%. And the fact that the stuff is “steel” means that the base is iron.
Stainless steels have room-temperature yield strengths that range from 205MPa (30kis) to more than 1725MPa (250 ksi). Operating temperatures around 750C (1400F) are reached. At the other extreme of temperature some stainless steels maintain their toughness down to temperatures approaching absolute zero.
With specific restrictions in certain types, the stainless steels can be shaped and fabricated in conventional ways. They can be produced and used in the as-cast condition; shapes can be produced by power-metallurgy techniques; cast ingots can be rolled or forged (and this accounts for the greatest tonnage by far). The roll product can be drawn, bent, extruded, or spun.
Stainless steel can be further shaped by machining, and it can be joined by soldering, brazing, and welding. It can be used as an integral cladding on plain carbon or low-alloy steels.
The generic term “stainless steel” covers scores of standard composition as well as variations bearing company trade names and special alloys made for particular applications. Stainless steels vary in their composition from a fairly simple alloy of, essentially, iron with 11% chromium, to complex alloys that include 30% chromium, substantial quantities of nickel, and half a dozen other effective elements. At the high-chromium, high-nickel end of the range they merge into other groups of heat-resisting alloys, and one has to be arbitrary about a cutoff point. If the alloy content is so high that the iron content is about half, however, the alloy falls outside the stainless family. Even with these imposed restrictions on composition, the range is great, and naturally, the properties that affect fabrication and use vary enormously. It is obviously not enough to specify simply a “stainless steel.”
Classification
The various specifying bodies categorize stainless steels according to chemical composition and other properties. However, all the stainless steels, whatever specifications they conform to, can be conveniently classified into six major classes that represent three distinct types of alloy constitution, or structure. These classes are ferritic, martensitic, austenitic,
manganese-substituted austenitic, duplex austenitic ferritic, and precipitation-hardening. Each class is briefly described below. (1)Ferrous stainless steels: This class is so named because the crystal structure of the steel is the same as that of iron at room temperature. The alloys in the class are magnetic at room temperature and up to their Curie temperature (about 750C ; 1400F). Common alloys in the ferrous class contain between 11% and 29% chromium, no nickel, and very little carbon in the wrought condition. (2) Martensitic stainless steels：Stainless steels of this class，which necessarily contain more than 11% chromium，have such a great hardenability that substantial thickness will harden during air cooling，and nothing more drastic than oil quenching is ever required. The hardness of the as-quenched martensitic stainless steel depends on its carbon content. However the development of mechanical properties through quenching and tempering is inevitably associated with increased susceptibility to corrosion. (3)Austenitic
stainless steels： The traditional and familiar austenitic stainless steels have a composition that
contains sufficient chromium to offer corrosion resistance，together with nickel to ensure austenite at room temperature and bellow. The basic austenitic composition is the familiar 18% chromium，8% nickel alloy. Both chromium and nickel contents can be increased to improve corrosion resistance, and additional elements (most commonly molybdenum) can be added to further enhance corrosion resistance. (4)Manganese-substituted austenitic stainless steels：The austenitic structure can be encouraged by elements other than nickel，and the substitution of manganese and nitrogen produces a class that we believe is sufficiently different in its properties to be separated from the chromium-nickel austenitic class just described. The most important difference lies in the higher strength of the manganese-substituted alloys. (5)Duplex
austenitic-ferrous stainless steels: The structure of these steels is a hybrid of the structures of ferrite and austenite; and the mechanical properties likewise combine qualities of each
component steel type. The duplex steels combine desirable corrosion and mechanical properties, and their use is as a result increasing in both wrought and cast form. (6)Precipitation-hardening stainless steels：Stainless steels can be designed so that their composition is amenable to precipitation hardening. This class cuts across two of the other classes，to give us martensitic and austenitic precipitation-hardening Stainless steels. In this class we find stainless steels with the greatest useful strength as well as the highest useful operating temperature.
Properties In selection of stainless steels，three kinds of properties have to be considered：(1)Physical properties: density, thermal conductivity, electrical resistivity, and so no; (2) Mechanical properties: strength, ductility, hardness, creep, resistance, fatigue, and so no; and (3) Corrosion-resistant properties. Note that properties of stainless steels are substantially influenced by chemical composition and microstructure. Hence specifications include chemical composition, or, more, correctly, an analysis of the most important elements (traces of unreported elements also may be present) as well as a heat treatment that provides the optimum structure.
Applications Since stainless steels were first used in cutlery industry, the number of applications has increased dramatically. The relative importance of the major fields of
applications for flat and long stainless steel products is shown in Table 1. Chemical and power engineering is the largest market for both long and flat products. It began in about 1920 with the nitric acid industry. Today, it includes an extremely diversified range of service conditions, including nuclear reactor vessels, heat exchangers, oil industry tubulars, components for the chemical processing and pulp and paper industries, furnace parts, and boilers used in fossil fuel electric power plants.
Application Industrial equipment Chemical and power engineering food and beverage industry transportation Percentage 34 18 9 Application Architecture Consumer goods Domestic application，house utensils Small electric and electronic application Percentage 5 28 6 (Selected from- Stainless Steels, Materials Park, ASM International, 1994. ) 材料6
不锈钢
不锈钢如其他一些钢材一样在大气中不会生锈。“不锈”意味着能够抵抗着色，生锈，空气中腐蚀，潮湿和污染，一般规定铬的含量在11%到30%。实际上钢铁材料意思是组成基础成分是铁。
不锈钢有室温的屈服应力从205 MPa (30 kis) 到超过 1725 MPa (250 ksi)。调整温度到750摄氏度（1400华氏度）左右就可以达到。在温度接近绝对0度时一些不锈钢获得良好的韧性。
一些类型的特殊限制条件，不锈钢能够通过惯常的方式被塑造和焊接。他们能够被生产和使用在铸造条件下，形状可以通过冶金技术获得，铸锭可以滚压或者锻造获得（归功于大型的吨压机）。轧制的产品能够被拉拔，弯曲，挤压或者旋转。不锈钢能够机械造型，能够通过焊接，铜焊等方法连接。它能够被用于整体的电镀于碳素和低合金钢。
一般的术语“不锈钢”有着标准的组成成分就好像变轴承公司交易名称和应用于特殊条件的特殊合金。不锈钢的构成多种多样，一种相当简单的合金，实质上，含铬11%，更复杂一点的合金那种含30%的铬，含大量的镍，和6种其他的有效元素。高铬，高镍他们合并为一种高抗性合金和一种截止点任意的合金。如果合金的含量太高，铁含量大概一半，这个合金就不是不锈家族的了。尽管在构成物上强加限制条件，不锈钢的分布任然是很大范围的，实际上，合金的使用非常的多。明显简单说不锈钢是不足够的。
分类 各种说明文根据化学成分和性能来划分不锈钢。然而，所有的不锈钢，不管是说明样的规格，它都可以简单的划分为6种等级代表了三种特有的合金构造或者结构。这些等级分别是铁素体，马氏体，奥氏体，锰代铬奥氏体，奥氏体铁素体双相和沉淀硬化型不锈钢。每种的简单描述如下：（1）亚铁不锈钢：这种命名是因为钢的晶体结构类似于铁在室温下的铁。这个等级的合金在室温下有磁性且能够接近居里温度(大概 750 C; 1400 F)普通的合金在亚铁等级包含11%到29%的铬，无镍，锻造条件下含有非常少的碳。（2）马氏体不锈钢，：这个等级的不锈钢必须包含超过11%的铬，有很强的硬度，空冷得时候非常的坚硬。淬火马氏体的硬度取决于其含碳量。然而，通过淬火和回火的机械性能的发展必然与腐蚀系数增加相关联。（3）奥氏体不锈钢：传统和常见的奥氏体不锈钢的结构成分包含了足够提供腐蚀抗力的铬和保证在室温下奥氏体在较低含量的镍。基础的奥氏体组成成分接近18%的铬，8%的镍合金。增加铬和镍的含量用以提高抗腐蚀能力，增加其他元素也能大大增强抗腐蚀能力。（4）锰代铬奥氏体不锈钢：奥氏体结构能够受到镍以外的元素的鼓舞，锰的替代物和氮生产出一个等级我们相信它的性能与上述所说的铬镍奥氏体充分的不一样。最重要的不同点是它是高强度的锰代铬合金。（5）奥氏体铁素体双相不锈钢：这种钢的结构师铁素体与奥氏体的混合物，这个的机械性能也一样是这两种钢型的结合。这种双相钢包含了令人满意的腐蚀和机械性能，它们在锻造和铸造上的使用也一直在增加。（6）沉淀硬化型不锈钢：不锈钢可以被设计成它们的成分服从沉淀硬化。这等级近似与其它的两个等级，给我们马氏体和奥氏体沉淀硬化型不锈钢。在这等级我们发现最大使用强度的不锈钢也有最高使用温度。
性能 在不锈钢的选择上，我们必须要考虑的三个性能：（1）物理性能：密度 导热性 电阻等等（2）机械性能：强度 韧性 硬度 延伸性 抗性 疲劳等等（3）抗腐蚀性能。注意不锈钢的性能影响是化学成分和微观结构的结果。因此说明书上要包含化学成分或者大部分重要的元素的分析和适合结构的温度治疗方法。
（选自，不锈钢R.A.Lula美国自然五金，1986） 应用 不锈钢最初是应用在餐具行业，应用量戏剧般的增加。一些相关的重要的应用领域和不锈钢的生产如图1所示。化学制品和力量工程应用市场最大。它开始于1920年和硝酸工业。今天，它包括及其多样的服役条件，包括原子反应堆容器，换热器和炼油器。
应用 工业设备 化工和电力工程 饮食业 运输业 （选自不锈钢，材料公园，美国金属协会，1994）
Reading Material 7
Standard Mechanical Tests
To summarize the previous discussion, it is very important to know the strength of a material, both for its eventual use and also to determine the forces required to shape it. Since it is impracticable to test every article after it has been designed and made, several simple general tests are used to measure the mechanical properties of the stock material before, during and after manufacture of the final product. (1) Tensile Tests
The simplest and most widely accepted tensile test requires a cylindrical (or flat) bar with enlarged ends. This tensile specimen is subjected to a steadily increasing tensile force along its axis, and the extension of a gauge length is accurately measured as the load-extension curve , according to the appropriate standard. The results usually required are the maximum tensile stress, the yield stress, the percentage elongation to fracture and the reduction of cross-sectional area at fracture. In addition, the Young’ s Modulus of Elasticity, or Young Modulus may be measured.
(2) Compression Tests
It is important for metal forming calculations to know the yield stress at much higher strains than can be obtained in tension. Axial compression of a short cylinder may be used, with suitable correction for the frictional resistance on the flat ends, but a more accurate result is obtained by the transverse plane strain compression of a well-lubricated strip. (3) Hardness Testing
Tensile and compression tests are destructive of the sample, but it is often important to check the strength properties of stock material or finished components, without destruction. There are several types of hardness test for this purpose, which make only a small indentation in the surface.
The oldest and best known hardness tests in the U.K are the Brinell test in which a standard ball (usually 10 mm dia. ) is pressed into a metal under a prescribed load, typically 3000 kgf (= 29. 42 kN or 6615 lbf), and the Vickers test. The Brinell Hardness Number (BHN or HB) is defined as the load in kgf divided by the actual spherical surface area of the indentation in mm2. Likewise, the Vickers Hardness Number (VHN or HV) is the load in kgf divided by the pyramidal surface area
百分数 34 18 9 应用 农业 生活用品 家庭用品，家庭器皿 小型电气化应用 百分数 5 28 6