1、1、When SI units are used,force is expressed in newtons(N) and area in square meters(m2).采用国际单位时，力用牛顿 (N) 表示，面积用平方米(m2) 表示。2、When using USCS units,stress is customarily expressed in pounds per square inch(psi) or kips per square inch(ksi).当用美国单位制时，应力通常用磅 /平方英寸或千磅/平方英寸表示。3、It is usually safe to assume
2、 that the formula =F/A may be used with good accuracy at within the bar that is at least a distance d away from the ends ,where d is the largest transverse dimension of the bar (see Fig.1-1a).假设公式 =F/A 能较好的适用于杆件内部离开两端距离至少不小于 d 的地方，这通常是安全的，此处 d 为杆的最大横向尺寸（图 1-1a)4、The principal requirement is that the
3、 deformation of the bar be uniform,which in turn requires that bar be prismatic ,the loads act through the centroids of the cross sections , and the material be homodgeneous (that is ,the same throughout all parts of the bar） 。主要的要求是棒的变形时均匀的，同时要求棒料是等截面杆、载荷通过横截面形心、材料是均质的（即杆件的所有部分相同）5、Capacity of a ma
4、chine component is related to the most severe service condition it can sustain without a change which will prevent the component from continuing its intended function .机器零件的承载能力是承受最恶劣的工作条件而不产生影响其功能的能力。6、Ultimate tensile strength( u）is the maximum nominal stress which can be observed in the stress-st
5、rain diagram,which corresponds to the maximum nominal stress that the material can sustain, the ratio of maximum load to the original cross-sectional area.最大拉伸强度 u 时最大的名义应力，这可从应力-应变图上看出来，对应于材料承受的最大名义应力，是最大载荷对初始横截面积的比值。7、Micro-cracks exist in the structure of this material which give rise to high str
6、ess concentration during tensile loading while in compressive loading, for geometrical reasons, these micro-cracks are ineffective.微裂纹存在于这种材料结构中，拉伸时导致较大的应力集中，而压缩时，因几何原因，这些微裂纹失去作用。8、 A hollow shaft weighs considerably less than a solid shaft of comparable strength, but is somewhat more expensive .在强度
7、相当的情况下，空心轴的重量比实心轴的要轻许多，但其加工成本比实心轴的要高。9、Careful location of bearings can do much to control the size of shafts, as the loading is affected by the position of mountings.由于零部件在轴上的安装位置对轴的受力有影响，因此，仔细地布局好轴承位置对控制轴的尺寸大小将很有帮助。10、Often, the bore of such other components has to be chamfered to clear radii at t
8、he point where a shaft changes diameter.通常，这类零件的孔须加工成锥面，以跳过轴颈变化处的过度半径。11、The diameters of shafts made compatible with metric-sized bores of mechanical components(such as antifriction bearings)are specified in millimeters.与机械零件（如滚动轴承）的米制尺寸的孔相配合的轴，其直径用毫米来规定。12、One rule of thumb is to restrict the tors
9、ional deflection to one degree in a length equal to 20 diameters.一种经验方法是，在每二十倍于直径的轴的长度上，扭转变形不超过 1 度。13、When two gears are meshing, the two pitch circles must be exactly tangent if the gears are to function properly.两齿轮啮合时，若要求它们正常运转，两齿轮的节圆必须相切。14、Pressure angle:the angle between the line of action(se
10、e Figure4-3)and a line perpendicular to the centerlines of the two gears in mesh.压力角：作用线与垂直于两啮合齿轮中心线的直线间的夹角。15、The metric system for spur-gear calculations involves more than changing inches to millimeters.采用米制进行直齿圆柱齿轮计算，所做的工作不仅仅是将英制换算成毫米。16、The module is found by dividing the pitch-circle diameter
11、by the number of teeth.节圆直径除以齿数便得到模数。17、The module is thus a dimension ,expressed in millimeters,equal to the reciprocal of the diametral pitch.因此，模数是一个线性尺度，用毫米表示，它等于径节的倒数。18、One should carefully determine horizontal force components, since these present problems designing the follower assembly guid
12、e.设计者应仔细分析水平力分量，因为它们会使从动件的导向出现问题，19、Again, forces need to be determined and dimensions chosen so as to avoid excessive component sizes.同样，需分析受力，选择尺寸，以避免零件尺寸过大。20、Some of them make it more comfortable or better looking,but most of them are to make it run.有些零件是让汽车更舒适、更美观，而大多数零件是用来使它运动的。21、This rotatio
13、n of both the wheels would result in slipping of one or both of them on the road surface causing excessive tyre wear as well as severe twisting loads on the shaft.这样转动将导致一只或两只后轮在路面上打滑，造成轮胎的过度磨损以及在驱动轴上产生严重的扭力载荷。22、Neither the ,misalignment resulting from the flexing of the vehicle structure over bump
14、y road surfaces can be avoided nor the precise alignment of shaft can be ensured without them.没有万向节，不仅因颠簸路面引起车身结构弯曲造成的不同轴线不能避免。而且轴的精确同轴也不能保证。23、Cores are placed in molds wherever it is necessary to preserve the space it occupies in the mold as a void in the resulting castings.型芯可放在铸型中需要之处，占据空间，以便在最后
15、的铸件中形成空间。24、Green sand generally consists of silica sand and additives coated by rubbing the sand grains together with clay uniformly wetted with water.型砂通常含有石英砂和添加剂，通常砂粒与水均匀溅湿的粘土的搅拌，使沙粒及添加剂表面包覆一层粘结薄膜。25、As a result ,the last portion of the casting to freeze will be deficient in metal and ,in the ab
16、sence of a supplemental metal-feed source,will result in some form of shrinkage.结果，在铸件最后凝固的部分会缺少金属，而且在缺少补缩金属源的补充时，将会产生一些缩孔。26、The pouring process must be carefully controlled,since the temperature of the melt greatly affects the degree of liquid contraction before solidification ,the rate of solidif
17、ication, which in turn affects the amount of columnar growth present at the mold wall,the extent and nature of the dendritic growth ,the degree of alloy burnout ,and the feeding characteristics of the risering system.浇注过程必须小心控制，因为熔化温度大大影响凝固前液态金属收缩的过程和凝固速率，这又将影响铸型中针状物成长的数量、程度和树枝状成长物的性质，合金溶蚀打的过程和冒口系统的
18、补缩特性。27、Again, productivity an quality depend to a large degree on the skill of the hammer operator and the tooling.同样地，生产率和质量在很大程度上取决于锻锤操作者的技巧和所用的工具。28、Closed-die forging relies less on operator skill and more on the design of the preform and forging dies.封闭摸锻造很少依赖操作者的技巧，而更多地取决于预成行模和锻造模的设计。29、Toler
19、ances vary with materials and design,but production runs calling for 0.002-to0.005-in.tolerance are regularly made.公差随材料和设计而变，但生产上通常需要 0.002-0.005 英寸的公差。30、Ring rolling offers a homogeneous circumferential grain flow,ease of fabrication and machining ,and versatility of material size.环状轧制可得到均质的周向纤维流
20、，易于制造和加工，可用于多种尺寸。31、Basically,are welding is a process in which an electric arc is produced between a metal electrode or wire carrying high-amperage current and the workpiece.从本质上来说，电弧焊是一种带大电流的金属电极或导线与工件之间产生电弧而进行焊接的方法。32、This type of electrode is used to advantage when the fit-up is poor and on shee
21、t metal where shallow penetration is desired.当焊接条件差，以及焊接薄板金属需要浅渗透时，可使用这种焊条。33、However,because of the heavy coating,there are about half as many rods per pound.然而，因涂层较重，每磅焊条数大约是其他涂层焊条的一半。34、However, it should be fully understood that any increase of strength over that of pure iron can be obtained onl
22、y at the expense of some loss of ductility ,and the final choice is always a compromise of some degree.然而，必须明白，要使强度高于纯铁的强度只有在损失塑性的情况下才能实现，因此，最综总是在塑性和强度之间形成某种折衷。35、Steels with approximately6 to 25 points of carbon(0.06-0.25）are rated as low carbon steels and are rarely hardened by heat treatment beca
23、use the low carbon content permits so little formation of hard martensite that the process is relatively ineffective.碳的质量分数大约 0.06-0.25的钢称为低碳钢，它们很难通过热处理淬硬，因为碳的含量太低，很难形成硬的马氏体结构，从而使热处理相对不起作用。36、Even plain carbon steels are alloys of at least iron,carbon ,and manganese,but the term alloy steel refers t
24、o steels containing elements other than these in controlled quantities greater than impurity concentration or ,in the case of manganese,greater than 1.5.即使是普通碳素钢，也是铁、碳和锰的合金，但合金钢中除了这些元素外，其他元素含量大于普通碳素结构钢的杂质含量，如锰的质量分数要大于 1.5。37、Any alloy generally shifts the transformation curves to the right ,which wi
25、th air cooling results in finer pearlite than would be formed in a plain carbon steel.所有合金通常使等温曲线右移，空冷时得到比普通碳钢细的珠光体。38、The carbon content may vary from very low to very high ,but for most steels it is in the medium range that effective heat treatment may be employed for property improvement at minim
26、um costs.碳含量可从很低变到很高，但大多数为中碳钢，可用最小成本热处理来有效改善性能。39、Plain low carbon steels,when fully annealed,are soft and relatively weak,offering little resistance to cutting,but usually having sufficient ductility and toughness that a cut chip tends to pull and tear the surface from which it is removed, leaving
27、a comparatively poor quality surface,which results in a poor machinability rating.当完全退火时，普通碳钢硬度较低，强度较小，对切削的阻力较小，但通常由于塑性和韧性太大以致切削离开工件表面时会划伤表面，工件表面质量比较差，导致较差的切削加工性。40、The machinability of many of the higher plain carbon and most of the alloy steels can usually be greatly improve by annealing, as they
28、are often too hard and strong to be easily cut at any but their softest condition .许多高碳钢和大多数合金钢的切削性通常可以退火大大改善，因为除在最软条件下，它们的硬度和强度太高而不易加工。41、The bainite structure is not as hard as the martensite that could be formed from the same composition, but in addition to reducing the thermal shock to which the
29、 steel would be subjected under normal hardening the thermal shock to perform any further treatment to develop good impact resistance in the high hardness range.贝氏体结构不如在同样成分时形成的马氏体硬，但除了减少钢在正常淬火时受到的热冲击外，不必要进一步处理，就可获得在高硬度时有好的冲击韧性。42、Similarly,a fit is indicated by the basic size common to both the mat
30、ing components,followed by the appropriate symbols corresponding to each component.类似的，配合可用相配零件的共同基本尺寸加上对应于每个零件的合适符号来表示。43、For example, fluid systems can transmit power more economically over greater distances than can mechanical types.例如，液压系统在长距离上比机械系统更能经济的传递动力。44、In short , very few people get thr
31、ough a day of their lives without somehow benefiting from the technology of hydraulics.简而言之，在日常生活中很少有人不从液压技术中得到某种益处。45、Pneumatic systems normally use a large centralized air compressor which is considered to be an infinite air source similar to an electrical system where you merely plug into an elec
32、trical outlet for electrical.气体系统通常考虑采用大的中央空气压缩机作为一个无限量的气源，这类似于电力系统，只要将插头插入插座便可获得电能。46、While pneumatic pressures are quite low due to compressor design limitations (less than 250psi),hydraulic pressures can be as high as 10,000 psi.Thus,hydraulics can be high-power systems,whereas pneumatics are confined to low-power applications.气压系统由于压缩机局限其系统压力相当低（低于 250psi） ，而液压力可达 10000psi 之高，因此液压系统可以是大功率系统，而气动系统仅限于小功率系统的应用。
