机械制造专业英语news重点语句.docVIP

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。 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。 It is usually safe to assume that the formula σ=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σ=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) The principal requirement is that the 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） Capacity of a machine 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。 Ultimate tensile strength( σu）is the maximum nominal stress which can be observed in the stress-strain 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σu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。 Micro-cracks exist in the structure of this material which give rise to high stress 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。 A hollow shaft weighs considerably less than a solid shaft of comparable strength, but is somewhat more expensive .在强度相当的情况下，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。 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