外文翻譯---機械零件強度

1、<p><b>　　附錄2</b></p><p><b>　　外文原文</b></p><p>　　THE Strength of Mechianical Elements</p><p>　　One of the primary considerations in designing any machine

2、of structure is that the strength must be sufficiently greater than the stress to assure both safety and reliability. To assure do fail. Then we shall be able to relate the stresses with the strengths to achieve safety.&

3、lt;/p><p>　　Ideally , in designing any machine clement, the engineer should have at his disposal the results of a great many strength tests of the particular material chosen. These tests shoule have been made o

4、n spccimens having the same heat treatment, surface roughness, and size as the element he proposes to design,and the tests should be made under exactly the same loading conditions as the part will experience in service.

5、This means that, if the part is to experience a bending load, it should be tested </p><p>　　You can now appreciate the following four design categories:</p><p>　　(1) Failure of the part would en

6、danger human life, or the part is made in extremely large quantities; consequently, an elaborate testing program is justified during design.</p><p>　　(2) The part is made in large enough quantities so that a

7、 moderate series of tests is feasible.</p><p>　　(3) The part is made in such small quantities that testing is not justified at all, or the design must be completed so rapidly that thert is not enough time fo

8、r testing.</p><p>　　(4) The part has already been designed, manufacturde, and tested and found to be unsatisfactory. Analysis is required to understand why the part is unsatisfactory and what to do improce i

9、t.</p><p>　　It is with the last three categories that we shall be mostly concerned. This means that the designer will usually have only published values of yield strength, ultimate strength, and percentage e

10、longation .With this meager information the engineer is expected to design against static and dynamic loads, biaxial and tri axial stress states,high and low temperatures, and large and small parts! The data usually avai

11、lable for design have been obtained from the simple tension test, where the load was </p><p>　　To sum up, the fundamental problem of the designer is to use the simple tension test data and relate them to the

12、 strength of the part, regardless of the stress state of the loading situation.</p><p>　　It is possible for two metals to have exactly the same strength and hardness, yet one of these metals may have a super

13、ior ability to absorb overloads, because of the property called ductility. Ductility is measured by the percentage elongation which occurs in the material at fracture. The usual dividing line between ductility and brittl

14、eness is 5 percent elongation. A material having less than 5 percent elongation at fracture is said to be brittle, while one having more is said to ductile. The e</p><p>　　When a material is to be selected t

15、o tesist weat, erosion, or plastic deformation, hardness is generally the most important. Sevetal methods of hardness testing are available, depending upon which particular property is most desired. The four hardness num

16、bers in greatest use are the Brinell, Rockwell, Vickers, and Koop. Most hardness-testing systems employ a standard load which is applied to a ball or pyramid in contact with the material to be tested. The hardness is the

17、n expressed as a function</p><p>　　Some Rules for Mechanical Design</p><p>　　Designing starts with a need, real or imagined. Existing apparatus may need improvements in durability, weight, speed

18、, or cost. New apparatus may be needed toperform a function previously done by men, such as computation, assembly, or servicing. With the objecive wholly or partly defined, the next step in design is the conception of me

19、chanisms and their arrangements that will perform the needed functions. For this, freehand sketching is of great value, not only as a record of one’s thoughts and </p><p>　　When the general shape and a few d

20、imensions of the several components become apparent, analysis can begin in earnest. The analysis will have as its objective satisfactory or superior perfromance, plus safety and durability with minimum weight, and a comp

21、etitive cost. Optimum proportions and dimensions will be sought for each critically loaded section, together with a balance between the strength of the several components. Materials and their treatment will be chosen. Th

22、ese important objectives c</p><p>　　Finally, a design based upon funtion and reliability will be completed, and a prototype may be built. If its tests are satisfactory, and if the device is to be produced i

23、n quantity, the initial design will undergo certain modifications that enable it to be manufactured in quantity at a lower cost. During subsequent years of manufacture and service, the design is likely to undergo changes

24、 as new ideas are conceived or as further analysis based upon tests and experience indicate altertions. Sales</p><p>　　To stimulate creative thought, the following rules are suggested for the designer.</p

25、><p>　　1、Apply ingenuity to utilize desired physical properties and to control undesired ones. The performance requirements of a machine are met by utilizing laws of nature or properties of matter(e.g, flexibil

26、ity, strength, gravity, inertia, buoyancy, centrifugal force, principles of the lever and inclined plane, friction, viscosity, fluid pressure ,and thermal expansion), also the many electrical, optical, thermal, and chemi

27、cal phenomena. However, what may be useful in one application may be detrimen</p><p>　　2、Provide for favorable stress distribute and stiffness with minimum weight. On components subjected to fluctuating stre

28、ss,particulat attention is given to a reduction in stress concentration, and to an increase of strength at fillets, threads, holes, and fits. Stress reduction are made by mondification in shape, and strengtening may be d

29、one by pre stressing treatments such as surface rolling and shallow hardening. Hollow shafts and tubing, and box sections give a facorable stress distribution, </p><p>　　3、Use basic equations to calculate an

30、d optimize dimensions. The fundamental equations of mechanics and the other sciences are the accepted bases for calculations. They are sometimes rearranged in special forms to facilitate the determination or optimization

31、 of demensions, such as the beam and surtace stress equations for determining geat-tooth size. Factors may be added to a fundamental equation for conditions not analytically determinable, e.g, on thin steel tubes, an all

32、owance forcorrosion add</p><p>　　4、Choose materials for a conbination of properties. Materials should be chosen for a conbination of pertinent properties, not only for strengths, hardness, and weight, but so

33、metimes for resistance to impact, corrosion, and low or high temperatures. Cost and fabrication properties are factors, such as weld ability, machine ability, sensitivity to cariation in heat-treating temperatures, and r

34、equired coating.</p><p>　　5、Select carefully between stock and integral components. A previously developed components is frequently selected by a designer and company from the stocks of parts manufacturers,

35、if the component meet the performance and reliability requirements and is adaptable without additional development costs to the particular machine being designed. However, its selecion should be carefully made with a ful

36、l knowledge of its properties, since the reputation and liability of the company suffer if there is</p><p>　　6、Provide for accurate location and non-interference of parts in assembly. A good design provides

37、for the correct locating of parts and for easy assembly and repair. Shoulders and pilot surfaces give sccurate location without measurement during assembly. Shapes can be designed so that parts cannot be assembled backwa

38、rds or in the wrong place. Interferences, as between screws in tapped holes, and between linkages must be foreseen and interference. Inaccurate alignment and positioning between detr</p><p><b>　　外文譯文&l

39、t;/b></p><p><b>　　機械零件強度</b></p><p>　　在設(shè)計任何機器或者結(jié)構(gòu)時，所考慮的主要事項之一是其強度應(yīng)該比它所承受的應(yīng)力要大得多，以保證安全與可靠性。要保證機械零件在使用過程中不發(fā)生失效，就必須知道它們在某些時候會失效的原因，然后，才能應(yīng)力與強度聯(lián)系起來，以保證其安全。</p><p>　　設(shè)計任何機械

40、零件的理想情況為：工程師可以利用大量的他所選擇的這種材料的強度試驗數(shù)據(jù)。這些試驗應(yīng)該采用與實際的零件有著相同的情況下進行。這表明，如果零件簡要進行承受彎曲載荷，那么就應(yīng)該進行彎曲載荷的試驗。這些種類的試驗可以提供非常有用和精度的數(shù)據(jù)。它們可以告訴工程師應(yīng)該使用的安全系數(shù)和對于給定使用壽命時的可靠性。在設(shè)計中，只要能夠獲得這些數(shù)據(jù)，工程師就可以盡可能好地進行工程設(shè)計工作。如果零件的失效可能危害人的生命安全，或者零件有足夠大的產(chǎn)量，則在設(shè)計

41、前搜集的這些廣泛的數(shù)據(jù)所花的費用是值得的。例如，汽車和冰箱的零件的產(chǎn)量非常大，可以在生產(chǎn)之前對它們進行的大量的試驗，使用具有較高的可靠性。如果把進行這些試驗的費用分攤到了所生產(chǎn)的零件上話，則分攤到所生產(chǎn)的每個零件上的費用非常低</p><p>　　你可以對下列四種類型的設(shè)計做出評價：</p><p>　　1、零件的失效可能危害人的生命安全，或者零件的產(chǎn)量非常的大，因此在設(shè)計時安排一個完善的

42、試驗程序會被認為是合理的。</p><p>　　2、零件的產(chǎn)量足夠大，可以進行適當(dāng)?shù)南盗性囼灐?lt;/p><p>　　3、零件的產(chǎn)量非常小，以至于進行試驗根本不合算；或者要求很快地完成設(shè)計，以至于沒有足夠的時間進行試驗。</p><p>　　4、零件已經(jīng)完成設(shè)計、制造和試驗，但結(jié)果不令人滿意。這時需要采用分析的方法來弄清不能令人滿意的原因和應(yīng)該如何進行改進。</

43、p><p>　　我們將主要對后三種類型進行討論。這就是說，設(shè)計人員通常只能利用那些公開發(fā)表的屈服強度，極限強度和延伸率等數(shù)據(jù)資料。人們期望工程師利用這些不是很多的數(shù)據(jù)資料的基礎(chǔ)上，對靜載荷與動載荷，二維應(yīng)力狀態(tài)與三維應(yīng)力狀態(tài)，高溫與低溫以及大零件與小零件進行設(shè)計，而設(shè)計中所能利用的數(shù)據(jù)通常是從簡單的拉伸試驗中得到的，其載荷是逐漸加上去的，有充分的時間產(chǎn)生應(yīng)變。到目前為止，還必須利用這些數(shù)據(jù)來設(shè)計每分鐘承受幾千次復(fù)雜的

44、動載荷和作用的零件，因此機械零件有時會失效是不足為奇的。</p><p>　　概括的說，設(shè)計人員所遇到的基本問題是，不論對于哪一種應(yīng)力狀態(tài)或者載荷情況，都能利用簡單的試驗所獲得的數(shù)據(jù)并將其零件的強度聯(lián)系起來?？赡軙袃煞N情況具有完全相同的強度和硬度值的金屬，其中一種由于本身的延展性而具有很好的承受超載荷的能力。延展性與脆性的分界線。斷裂時延伸率小于5%的材料稱為脆性材料，大約5%的稱為延性材料。材料的伸長量通常是

45、在50mm的計量長度上測量的。因為這并不是對實際應(yīng)變量的測量，所以有時也采用另一種測量延展性的方法。這個方法是在試件斷裂后，測量其斷裂處的橫截面的面積。因此，延展性可以表示為橫截面的收縮率。延性材料能夠承受較大的超載荷這個特性，是設(shè)計中的附加安全因素。延性材料的重要性在于它是材料冷變形性能的衡量尺度。諸如彎曲和拉伸這種金屬加工過程需要采用延性材料。</p><p>　　在選用抗磨損、抗腐蝕或者抗變形的材料時，硬度

46、通常是最主要的性能。有幾種可供選擇的硬度試驗反復(fù)法，采用哪一種方法取決于最希望測量的材料特性。最常用的四種硬度數(shù)值是步氏硬度、洛氏硬度、維氏硬度和努氏硬度。大多數(shù)硬度試驗系統(tǒng)是將一個標準的載荷加在與被試驗材料相接觸的小球或者棱錐上。因此，硬度可以表示為所產(chǎn)生的壓痕尺寸的函數(shù)。這表明由于硬度是非破壞性的試驗，而且不需要專門的試件，因而，硬度是一個容易測量的性能。通常可以直接在實際的機械零件上進行硬度試驗。</p><p

47、><b>　　機械設(shè)計規(guī)則</b></p><p>　　設(shè)計是從實際或者假象的需要開始的，對于現(xiàn)有的設(shè)備可能需要在耐用性，效率進度成本等方面做進一步改進工作，也可能需要新的設(shè)備完成以前由人來做的工作，例如計算機或者裝配。當(dāng)目標完成或部分被確定以后，下一步設(shè)計步驟是對能夠完成所需要的機構(gòu)及其布局進行總體設(shè)計。對于此項工作，徒手畫的草圖是很有價值的，它不僅可以記錄下我們的想法，而且還有助于

48、與別人進行討論，特別是和自己的大腦記性交流，從而促進創(chuàng)新想法的產(chǎn)生。</p><p>　　當(dāng)一些零件的大致形狀和幾個尺寸被確定后，就可以開始認真的分析工作。分析工作的目的是要在重量最輕、成本最低的情況下，令人滿意，即優(yōu)良的工作性能，并且還要安全耐用。對于每個關(guān)鍵承載截面，應(yīng)該尋求最佳的比例和尺寸，同時要對這幾個零件的受力進行平衡。要對材料和處理方式進行選擇。只有根據(jù)力學(xué)原理進行分析才能達到這些重要目的。這些分析包

49、括根據(jù)靜力學(xué)原理分析反作用力和充分利用摩擦力，根據(jù)動力學(xué)原理分析慣性、加速度和能量；根據(jù)彈性力學(xué)和材料力學(xué)分析應(yīng)力和變形；根據(jù)流體力學(xué)來分析潤滑和流體傳動。</p><p>　　最后，完成基本功能要求和可靠性所進行的設(shè)計，且要制作一臺樣機。如果試驗結(jié)果令人滿意，而且該裝置將要進行批量生產(chǎn)，就應(yīng)該對最初提出的設(shè)計方案做出一些修改，是其能以比較低的成本進行批量生產(chǎn)。在以后的制造和使用期內(nèi)，如果產(chǎn)生了新的想法或者根據(jù)試

50、驗和經(jīng)驗所做的進一步分析結(jié)果表明，可以有更好的替代方案，則很可能對原設(shè)計方案進行修改。銷售吸引力、客戶的滿意程度和制造成本均與設(shè)計有關(guān)，而設(shè)計能力則與工程創(chuàng)新是密切相關(guān)的。</p><p>　　為激發(fā)創(chuàng)造性思維，建議設(shè)計人員遵循下列準則：</p><p>　　1、創(chuàng)造性地利用所需要的物理性能和控制不需要的物理性能?？梢岳米匀环▌t或物理性能（例如柔性、強度、重力、慣性、浮力、離心力、杠桿原

51、理和斜面原理、摩擦、粘性、流體壓力和熱膨脹）和許多電學(xué)、光學(xué)和化學(xué)現(xiàn)象來滿足一臺機器的設(shè)計要求。一種性能在某種場合下可能是有用的，而在另外一種場合下則可能是有害的。閥門的彈簧應(yīng)該有柔性，而閥門的凸輪就不需要柔性。離合器結(jié)合面上需要有摩擦，而離合器軸承卻不需要摩擦。設(shè)計時，需要創(chuàng)造性地利用和控制所要的物理性能，將不需要的物理性能減小至最小。</p><p>　　2、在重量最輕的情況下，提供合理的應(yīng)里分布和剛度。對于

52、承受交變應(yīng)力的零件應(yīng)該特別注意減輕應(yīng)力集中和提高圓角，螺紋和配合處的強度。改變零件的形狀，可以降低它所承受的應(yīng)力，對零件施加預(yù)緊力，如表面滾壓和淺表面硬化，均可使其得到強化?？招妮S和空心管道，箱形截面能獲得有利的應(yīng)力分布，同時具有強度高而重量最輕的特點。曲軸，凸輪以及含有軸承支座的外殼和構(gòu)架都具有足夠的剛度以保證直線對中精度和接觸表面之間的壓力均勻分布。軸和其它零件須有適當(dāng)?shù)膭偠龋苊猱a(chǎn)生共振。</p><p>

53、　　3、利用基本公式進行尺寸計算和尺寸優(yōu)化。力學(xué)和其他學(xué)科的基本公式是公認的計算依據(jù)。有時需要見這些公式進行移項而化成特殊形式，以簡化尺寸的計算或者對尺寸進行優(yōu)化。例如，用梁的表面應(yīng)力公式來計算齒輪的輪齒尺寸。在不能采用解析法計算的情況下，可以在基本公式內(nèi)引入系數(shù)。例如，對于薄壁鋼管，考慮到腐蝕性，可以根據(jù)壓力求得的厚度增加一些。若必須應(yīng)用一個基本公式來確定形狀、材料和使用條件，而這些被確定的量值僅僅與在公式推導(dǎo)中的假設(shè)比較接近時，要采

54、取措施使結(jié)果“偏于安全”。當(dāng)數(shù)據(jù)不完全時，可以應(yīng)用理論公式作為尺寸的指南，在擴展后的范圍內(nèi)獲得令人滿意的設(shè)計結(jié)果。</p><p>　　4、根據(jù)性能組合選擇材料。選擇材料時需要考慮強度，硬度和重量，而且有時還要考慮抗沖擊性，抗腐蝕性和耐高溫或低溫的能力。成本和制造性能都是應(yīng)該考慮的因素，這些因素包括可焊接性，機械加工性能，對熱處理溫度變化的敏感性和所需要的涂層性等</p><p>　　5、

55、在現(xiàn)有的零件和整體零件之間進行認真的選擇。若一個以前研制的零件能夠滿足要求和可靠性要求，并使用于所設(shè)計的那臺機器而附加的研制費用，那么設(shè)計人員及其公司通常會從零件制造廠的現(xiàn)貨中選取該零件。但是，只有充分了解其性能，才能進行認真的選擇工作，因為任何一個機器零件的失效都會影響公司的信譽，并使公司承擔(dān)相應(yīng)的責(zé)任，在其他情況下，若機器設(shè)計人員自己來設(shè)計零件，則零件的強度，可靠性和成本等方面的要求就可以更好的得到滿足?？蓪⒛硞€零件與其他零件設(shè)計成