幾篇機械專業(yè)英語翻譯

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）應力和應變?當一個力（或負載）被施加到一個材料，它?人。的應力作用于產生的應力中的材料。應力作用于材料是每單位面積施加的力：?應力可能拉伸，?剪切性質。壓縮或剪切的性質圖l。圖3示出了金屬板張力，即的力F是一拉伸力。因而才的塊長度增加并降低其橫截面中，如果金屬塊具有剖區(qū)域

8、A中，則拉伸應力是F / A?的尺寸變化由應力引起的被稱為應變。在張力（或壓縮），應變的比率?改變到原長度的長度。從而圖1。 3 ?作為一個比例，應變是一個沒有單位的數(shù)量，但改變 ?無論是在長度和原始長度必須在表示相同的單位。也可以是表達GFP的應變?yōu)榘俜直取??在圖1.4中，力F壓縮的金屬，從而減少它的長度和增加其橫截面中。在這的情況下，壓縮應力為F / A和 在彈性行為，應變在預應力材料生產是只要完全刪除資料顯示彈性性能相當總高應力，而另一些有一點，如有的話，彈性?當由彈性材料被加載?逐步緊張，彈性直接產生的應變成比例的應力造成它。這種關系被稱為虎克定律。應力的曲線圖中和菌株（圖1 5）將

9、是一個直線傳遞思想的起源。秒;氧化聚乙烯的這?直線：（應力/應變）是一個對于一個給定的材料常數(shù) ?此常數(shù)稱為楊氏模量?；蚰椥裕⑶冶槐硎緸镋，使由于應變是無量綱量，E具有相同的壓力的單位。 E的值的性質受的材料;鋼，它是關于 ，而不是很大影響的組合物，或熱處理，但?隨著溫度的增加而減小。該值越高更有彈性的材料是電子。?：: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.剪毛金屬切割強調它高于其在高于其剪切剪切極限強度相鄰的鋒利的邊緣，如圖平沖頭和模

15、具如該圖所示，需要一個最大的功率。為了減少剪切力的沖頭或 模具應在角度，從而使切削行動是漸進的。這個分配的剪?切作用 在更大的行程長度，可以降低功率需要。最多t0時刻的50。消隱的操作如圖5.4所示，切出平坦區(qū)域為所需的形狀，它通常是第一個 在一系列的操作步驟。在這種情況下，沖頭 是平坦的，模具給出一些剪切角，使得 完成部分將持平。沖孔或穿孔孔金屬，金屬邊緣，開槽或打孔都類似的操作。對于這些操作的剪切角是 沖頭和除去的金屬廢料。修剪是除去“閃光”或多余的金屬從邊緣周圍的 的一部分和在本質上是相同的消隱。剃須 類似的，只不過它是整理或上漿工藝的。分切 不完整的削減工作表中，如圖5。 5。如果孔部

16、分沖壓，一面彎下腰成百葉門，它被稱為穿刺。所有這些操作可能 相同類型的印刷機上完成，并一點除了在不同 所使用的模具。的沖頭和模具之間的間隙的量消隱的厚度和種股票。薄料沖頭應該是一個緊密滑動配合。為較重的股票的間隙必須創(chuàng)建沖頭大。(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