几篇机械专业英语翻译

1、(B) Stress and StrainWhen a force (or load) is applied to a material,ital. The stress acting on theproduces a stress in the material.the stress acting on thematerial is the force exerted per unit area:Stresses may be tensile,shear in pressive or shear in natureFigure l. 3 shows a metal blo

2、cktension,i.e. the force F isastretching force . which thusincreases the length of the blockand reduces its cross-section If themetal block has a cross sectionalarea A,then the tensile stress isF/AThe dimensional changecaused by a stress is called strain.In tension (or compression), the strain is th

3、e ratio of thechange in length to the original length.Thusfigure 1. 3Being a ratio, strain is a number without units,but changeboth in length and original length must be expressed in thesame units. Strain may also be expresse as a percentage.In figure 1.4, the force F compresses the metal,thusreduci

4、ng its length and increasing its cross-section. in thiscase,the compressive stress is F/A andIn elastic behavior,the strainproduced in a stressed material iscompletely removed as soon as thematerials show elastic properties up to fairly hight stresses,while others have little ,if any ,elasticityWhen

5、 an elastic material is loadedprogressively in tension, the elasticstrain produced is directlyproportional to the stress causingit,. This relationship is known asHookes law. The graph of stressagainst strain (fig. 1. 5) will be astraight line passing thought the origin .the s;ope of thisstraight lin

6、e: (stress/strain)is a constant for a given material this constant is known as Youngs modulus. or the modulus of elasticity,and is denoted be E,so thatSince strain is a dimensionless quantity, E has the sameunits as stress. The value of E is governed by the nature ofthe material; for steel it is abo

7、ut and is notmuch affected by composition or heat treatment, butdecreases with increase in temperature. The higher the value of E the more springy a material is.（B）应力和应变?当一个力（或负载）被施加到一个材料，它?人。的应力作用于产生的应力中的材料。应力作用于材料是每单位面积施加的力：?应力可能拉伸，?剪切性质。压缩或剪切的性质图l。图3示出了金属板张力，即的力F是一拉伸力。因而才的块长度增加并降低其横截面中，如果金属块具有剖区域

8、A中，则拉伸应力是F / A?的尺寸变化由应力引起的被称为应变。在张力（或压缩），应变的比率?改变到原长度的长度。从而图1。 3 ?作为一个比例，应变是一个没有单位的数量，但改变 ?无论是在长度和原始长度必须在表示相同的单位。也可以是表达GFP的应变为百分比。 ?在图1.4中，力F压缩的金属，从而减少它的长度和增加其横截面中。在这的情况下，压缩应力为F / A和 在弹性行为，应变在预应力材料生产是只要完全删除资料显示弹性性能相当总高应力，而另一些有一点，如有的话，弹性?当由弹性材料被加载?逐步紧张，弹性直接产生的应变成比例的应力造成它。这种关系被称为虎克定律。应力的曲线图中和菌株（图1 5）将

9、是一个直线传递思想的起源。秒;氧化聚乙烯的这?直线：（应力/应变）是一个对于一个给定的材料常数 ?此常数称为杨氏模量。或模弹性，并且被表示为E，使由于应变是无量纲量，E具有相同的压力的单位。 E的值的性质受的材料;钢，它是关于 ，而不是很大影响的组合物，或热处理，但?随着温度的增加而减小。该值越高更有弹性的材料是电子。?：:shearingcutting metal involves stressing it shear above its in shear above itsultimate strength between adjacent sharp edges as shown in

10、figureFlat punches and dies as shown in the figure require amaximum of power. To reduce the shear force the punch ordie should be made at angle, so that the cuttingaction is progressive . this distributes the shearing actionover a greater length of the stroke and can reduce the powerrequired. by up

11、t0 50%.Blanking as shown in Figure 5.4, is the operation ofcutting out flat areas to a desired shape .It is usually the firststep in a series of operations. in this case the punch shouldbe flat and the die given some shear angle so that the finished part will be flat. Punching or piercing holes in m

12、etal, notching metal from edges, or perforating are allsimilar operations. For these operations the shear angle is on the punch and the metal removed is scrap. Trimming is the removal of flash or excess metal from around the edges of a part and is essentially the same as blanking. Shaving is similar

13、 except that it is a finishing or sizing process .slitting is making incomplete cuts in a sheet as illustrated in Figure5. 5. If a hole is partially punched and one side bent down as a louver, it is called lancing. All these operations may be done on presses of the same type and differ little except

14、 in the dies that are used.the amount of clearance between a punch and die forblanking is determined by the thickness and kind of stock. For thin material the punch should be a close-sliding fit. For heavier stock the clearance must larger to create the punch.剪毛金属切割强调它高于其在高于其剪切剪切极限强度相邻的锋利的边缘，如图平冲头和模

15、具如该图所示，需要一个最大的功率。为了减少剪切力的冲头或 模具应在角度，从而使切削行动是渐进的。这个分配的剪?切作用 在更大的行程长度，可以降低功率需要。最多t0时刻的50。消隐的操作如图5.4所示，切出平坦区域为所需的形状，它通常是第一个 在一系列的操作步骤。在这种情况下，冲头 是平坦的，模具给出一些剪切角，使得 完成部分将持平。冲孔或穿孔孔金属，金属边缘，开槽或打孔都类似的操作。对于这些操作的剪切角是 冲头和除去的金属废料。修剪是除去“闪光”或多余的金属从边缘周围的 的一部分和在本质上是相同的消隐。剃须 类似的，只不过它是整理或上浆工艺的。分切 不完整的削减工作表中，如图5。 5。如果孔部

16、分冲压，一面弯下腰成百叶门，它被称为穿刺。所有这些操作可能 相同类型的印刷机上完成，并一点除了在不同 所使用的模具。的冲头和模具之间的间隙的量消隐的厚度和种股票。薄料冲头应该是一个紧密滑动配合。为较重的股票的间隙必须创建冲头大。(A) Tlhe L and C Elementsthe reaction of a coil or capacitor to an ac signal isquite different from that of a resistor。 Both will limit themagnitude of the current ， but neither (ideally

17、 speaking) willdissipate any of the electrical energy delivered to it. It willsimply store it in the form of a magnetic field for theinductor，or electric field for the capacitor, with the abilityto return it to the electrical system as required by design.For the incluctor the reactance to an ac sIgn

18、al isdetermined byEquation (10-3) reveals that the inductive reactance isdirectly proportional to the frequency of the applied signalRecall that the ideal inductor had a short-circuit equivalentin dc steady-state systems. Certainly for dc f=0 and wefind that the reactance of the inductor is XL = , s

19、upporting that conclusion. At very highfrequencies, the equivalent circuit takes on thecharacteristics of an open-circuit since the resultingreactance is so high.A sinusoidal voltage has been applied across a 0. 5-Hincluctor in Fig.l0. 3. The reactance of the inductor at theapplied frequency is 188.

20、 5(7. Ohms law can then be appliedto determine the peak value of the current. that is, .the inductor leads the resulting current by 90. Theinductor, therefore 9 introducesa 90 phase shift between thetwo quantities not present for the pure resistor,for the pure capacitor the reactance is determinded

21、byindicating that as the frequency increases the reactance of acapacitor decreases (opposite to that of the inductor). Inaddition for f=O, corresponding with. the dc condition, Xc=1/0C = =.very large value, corresponding with anopen-circuit equivalent asdescribed fordc network .At very low frequenci

22、es the characteristics of a capacitor approach those of a short-circuit.A sinusoidal voltage has been applied across a lOuFcapacitor in Fig.l0- 4. The reactance X as shown in thefigure is 265.25 and the peak value of the current can be determined through a simple application of Ohms law that is,as show in Fig.10. 4. Note in this case that a 90 phaseshift has been intr