possible tool life. Machinability applies to（应用于） the tool-work（工具，零件） combination. It is not determined by hardness（硬度） alone, but by the 工性是刀具和零件的结合。 加工性不仅仅只由硬度决定，它还由韧toughness（韧性）, microstructure, chemical composition（成分）, 性，微观结构，化学成分和在冷加工下金属and tendency（倾向） of a metal to harden under cold work. In the 所呈现的硬化特性所决定。在容易混淆的表misleading expression “too hard to machine”, the word “hard” 示“难加工”中，“hard”与“difficult”is usually meant to be synonymous（同义的） with “difficult”. Many 同义。许多时候，因为材料过软而难于稳定times a material is actually too soft to machine readily. Softness 加工。材料柔软性和韧性能够产生金属撕裂，and toughness may cause the metal to tear（撕裂） and flow ahead 使金属在完成切削前流动至刀具前端。柔软of the cutting tool rather than cut cleanly. Metal that are 的金属往往会被加入合金从而牺牲它的延展inherently（天性地，固有地） soft and tough are sometimes alloyed 性来提高加工性能。如黄铜中加入铅钢中加to improve their machinability at some sacrifice（牺牲） in 入硫磺。 ductility. Examples are use of lead（铅） in brass（黄铜） and of sulfur（硫磺） in steel. Machinability is a term used to indicate the relative（比较的） tools in operations such as turning（车）, drilling（钻）, milling（铣）, broaching（拉削）, and reaming（铰）. In the machining of metal, the metal being cut, the cutting 在对金属进行加工时，被切削的金属，切机械加工性能是在指对工件材料使用刀难易程度。 ease（不费力） with which a material can be machined by sharp cutting 具进行诸如车、钻、铣、拉削、铰加工时的tool, the coolant, the process and type of machine tool（机床）, 削刀具，冷却液，使用的机床的种类，切削and the cutting conditions all influence the results. By changing 条件均影响着切削效果。改变任何一种均会any one of these factors, different results will be obtained. The 产生不同的切削效果。切削效果评定的准则criterion（标准） upon which the ratings（等级） listed are based(等是：车削时在固定的切削条件下产生一定量级评定的标准) is the relative volume of various（不同种） materials 的刀具磨损时，被加工试件相应的材料去除that may be removed by turning under fixed conditions to produce 量。 an arbitrary（任意的） fixed amount of tool wear.
Unit 3 Mechanical Properties of Materials
The material properties can be classified into three major headings: (i) Physical, (ii) Chemical, (iii) Mechanical. ------------------------------------------------- Physical properties Density or specific gravity, moisture content, etc., can be classified under this category. ----------------------------------- Chemical properties Many chemical properties come under this category. These 材料特性主要分为三类：(i)物理特性，(ii)化学特性，(iii)力学性能。 ------------------------------------ 物理特性 范畴。 ----------------------------------- 化学特性 许多化学特性都归入到这个范畴。其密度或特定的重力，湿度等都属于此include acidity or alkalinity, reactivity and corrosion. The 中包括酸性或碱性，活性和耐腐蚀性。而在这其most important of these is corrosion which can be explained in 中最重要的是耐腐蚀性，通俗的解释是材料在特layman’s terms as the resistance of the material to decay while 定大气中长期使用时，抵抗腐蚀的能力。 in continuous use in a particular atmosphere. ----------------------------------- Mechanical properties Mechanical properties include the strength properties like tensile, compression, shear, torsion, impact, fatigue and creep. maximum load, which the specimen bears by the area of cross-section of the specimen. ----------------------------------- This is a curve plotted between the stress along the a tensile test. A material tends to change or changes its the load. When the load is removed it can be seen that the ----------------------------------- 力学特性 力学特性包括诸如拉伸，压缩，剪切，The tensile strength of a material is obtained by dividing the 扭转，冲击，疲劳和蠕变等强度特性。一种材料的拉伸强度由试件承载的最大载荷除以试件的横截面积得到。 ----------------------------------- 如图所示为在拉伸试验中沿着X轴Y-axis(ordinate) and the strain along the X-axis(abscissa) in （横轴）的应变和沿着Y轴（纵轴）的应力之间的关系曲线。材料在加载时，随着载荷大小的变于许多材料来说，上述情况发生的应力极限值称dimensions when it is loaded, depending upon the magnitude of 化，尺寸会发生改变。当卸载时，变形消失。对deformation disappear s. For many materials this occurs up to 为弹性极限。在应力-应变曲线中，直线关系和a certain value of the stress called the elastic limit. This is 随后的小小的弯曲描述了上述的加载和卸载。 depicted by the straight line relationship and a small deviation thereafter, in the stress-strain curve. ----------------------------------- Within the elastic range, the limiting value of the stress -----------------------------------在弹性范围内，应力应变成比例的应力极限up to which the stress and strain are proportional, is called 值称为比例极限。在这个区域中，金属服从胡克the limit of proportionality. In this region, the metal obeys 定律—阐述了在加载的弹性范围内，应力和应变Hooke’s law, which states that the stress is proportional to 成比例关系（材料在卸载后，能够完全回复它原strain in the elastic range of loading (the material completely 来的尺寸）。在曲线的实际绘制中，比例极限值regains its original dimensions after the load is removed). In 要稍微比弹性极限值低。这可能是由于材料回复the actual plotting of the curve, the proportionality limit is 原尺寸需要的时间延迟。这种现象在一些有色金obtained at a slightly lower value of the load than the elastic 属中常常出现。 limit. This may be attributed to the time-lag in the regaining of the original dimensions of the material. This effect is very frequently noticed in some no-ferrous metals. ----------------------------------- While iron and nickel exhibit clear ranges of elasticity, ----------------------------------- 铁和镍存在明显的弹性范围，铜，锌，copper, zinc（锌）, tin（锡）, etc, are found to be imperfectly 锡等即使在相当低的应力值下弹性也表现得不elastic even at relatively（相当地） low values of stresses. 是很充分。实际上依靠测试仪器的精确性可以使Actually the elastic limit is distinguishable（可区分的） from 比例极限和弹性极限区分得更清晰。 the proportionality（比例性） limit more clearly depending upon the sensitivity（灵敏性） of the measuring instrument. ----------------------------------- When the load is increased beyond the elastic limit, plastic deformation starts. Simultaneously the specimen gets ----------------------------------- 当在弹性极限之上增大载荷时会产生塑性变形。同时，试件发生加工硬化。到达某点后变形的速度快于载荷增加的速度。这一点叫做work-hardened. A point is reached when（这时） the deformation 屈服极限点。一开始一直在抵抗载荷的金属在这starts to occur more rapidly than the increasing load. This point 一点后开始迅速地发生形变，也就是，屈服。屈is called the yield point Q. the metal which was resisting the 服应力叫做屈服极限。 load till then, starts to deform somewhat rapidly, i. e. , yield. The yield stress is called yield limit. ----------------------------------- The elongation of the specimen continues form Q to S and ----------------------------------- 试件从Q到S在到T不断地延长。在then to T. the stess-strain relation in this plastic flow period 这个塑性流动期间的应力-应变关系表示为曲线is indicated by the portion QRST of the curve. At T the specimen 上的QRST段。在T点试件断裂，此时的载荷称breaks, and this load is called the breaking load. The value of 为断裂载荷。最大荷载值S除以试件的横截面积the maximum load S divided by the original cross-sectional area 为金属的最大拉伸强度或简单地称为拉伸强度。 of the specimen is referred to as the ultimate tensile strength of the metal or simply the tensile strength. ----------------------------------- ----------------------------------- 逻辑上来说，一旦超过弹性极限，金Logically speaking, once the elastic limit is exceeded, the 属应该就会屈服直至最后断裂，在应力值上应该metal should starts to yield, and finally break, without any 没有增加。但是实际的曲线却记录了在超过弹性increase in the value of stress. But the curve records an 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. The more plastic deformation the metal undergoes, the elongated the more its diameter(and hence, cross-sectional area) is decreased. This continues until the point S is reached. ----------------------------------- After S, the rate at which the redution in area takes place, 极限后的增加了的应力。这种现象的发生可能有1. 材料的应变强化； 2. 由于塑性变形引起的试件横截面积的缩小。 由于加工硬化，金属在发生塑性变形时会变得越来越硬。金属拉伸越长它的直径 ----------------------------------- 超过S点后，面积减少的速度超过了increased stress even after the elastic limit is exceeded. Two 两种原因： harder it becomes, due to work-hardening. The more the metal gets 越小。这种现象一直持续到曲线上的S点。 exceeds the rate at which the stress increases. Strain becomes 应力增加的速度。应变变得很大，面积的减少在so high that the redution in area begins to produce a localized 某些点产生了局部效应。叫做颈缩。 effect at some point. This is called neching. ----------------------------------- Reduction in cross-sectional area takes place very -----------------------------------横截面积减小的速度非常快；以至于实际上rapidly; so rapidly that the load value actully drops. This is 载荷降低。 indicated by ST. Failure occurs at this point T. ----------------------------------- the ductility or plasticity of the material: Where and are the original and the final length of the specimen; and are the original and the final cross-sectional area.
----------------------------------- 伸长率和面积减少率表示了材料的延 Then percentage elongation and reduction in area indicate 展性。
Unit5 Design of machine and machine elements
机器和机器零件的设计
Machine design Machine design is the art of planning or devising new or improved machines to accomplish specific purposes. In general, a machine will consist of a combination of several different mechanical elements properly designed and arranged to work together, as a whole. During the initial planning of a machine, fundamental decisions must be made concerning loading, type of kinematic elements to be used, and correct utilization of the properties of engineering materials. Economic considerations are usually of prime importance when the design of new machinery is undertaken. In general, the lowest over-all costs are designed. Consideration should be given not only to the cost of design, manufacture the necessary safety features and be of pleasing external appearance. The objective is to produce a machine which is not only sufficiently rugged to function properly for a reasonable life, but is at the same time cheap enough to be economically feasible. The engineer in charge of the design of a machine should not only have adequate technical training, but must be a man of sound judgment and wide experience, qualities which are usually acquired only after considerable time has been spent in actual professional work. Design of machine elements 机器设计 机器设计为了特定的目的而发明或改进机器的一种艺术。一般来讲，机器时有多种不同的合理设计并有序装配在一起的部件构成的，在最初的机器设计阶段，必须基本明确负载、元件的运动情况、工程材料的合理使用性能。负责新机器的设计最初的最重要的是经济性考虑。一般来说，选择总成本最低的设计方案，不仅要考虑设计、制造、销售、安装的成本。还要考虑服务的费用，机械要保证必要的安全性能和美观的外形。制造机器的目标不仅要追求保证只用功能的合理寿命，还要保证足够便宜以同时保证其经济的可行性。 负责设计机器的工程师，不仅要经过专业的培训，而且必须是一个准确判断而又有丰富经验的人，具有一种有足够时间从事专门的实际工作的素质。 机器零件的设计 相同的理论或方程可应用在一个一起的非常小的零件上，也可用在一个复杂的设备的大型相似件上，既然如此，毫无The principles of design are, of course, universal. The same theory 疑问，数学计算是绝对的和最终的。他们or equations may be applied to a very small part, as in an 都符合不同的设想，这必须由工程量决定。instrument, or, to a larger but similar part used in a piece of 有时，一台机器的零件全部计算仅仅是设heavy equipment. In no ease, however, should mathematical 计的一部分。零件的结构和尺寸通常根据calculations be looked upon as absolute and final. They are all 实际考虑。另一方面，如果机器和昂贵，subject to the accuracy of the various assumptions, which must 或者质量很重要，例如飞机，那麽每一个necessarily be made in engineering work. Sometimes only a portion 零件都要设计计算。 of the total number of parts in a machine are designed on the basis of analytic calculations. The form and size of the remaining parts 当然，设计计算的目的是试图预测are designed on the basis of analytic calculations. On the other 零件的应力和变形，以保证其安全的带动hand, if the machine is very expensive, or if weight is a factor, 负载，这是必要的，并且其也许影响到机as in airplanes, design computations may then be made for almost 器的最终寿命。当然，所有的计算依赖于all the parts. 这些结构材料通过试验测定的物理性能。 The purpose of the design calculations is, of course, to 国际上的设计方法试图通过从一些相对简attempt to predict the stress or deformation in the part in order 单的而基本的实验中得到一些结果，这些that it may sagely carry the loads, which will be imposed on it, 试验，例如结构复杂的及现代机械设计到and that it may last for the expected life of the machine. All 的电压、转矩和疲劳强度。 calculations are, of course, dependent on the physical
机械设计制造及其自动化专业英语unit1-3,5-7,4 - 图文
