外文翻譯--機器和機器零件的設(shè)計

1、<p>　　Machine design</p><p>　　Machine design is the art of planning or devising new or improved machines to accomplish specific purposes. In general, a machine will consist of a combination of several d

2、ifferent mechanical elements properly designed and arranged to work together, as a whole. During the initial planning of a machine, fundamental decisions must be made concerning loading, type of kinematic elements to be

3、used, and correct utilization of the properties of engineering materials. Economic considerations are usuall</p><p>　　The engineer in charge of the design of a machine should not only have adequate technical

4、 training, but must be a man of sound judgment and wide experience, qualities which are usually acquired only after considerable time has been spent in actual professional work.</p><p>　　Design of machine el

5、ements</p><p>　　The principles of design are, of course, universal. The same theory or equations may be applied to a very small part, as in an instrument, or, to a larger but similar part used in a piece of

6、heavy equipment. In no ease, however, should mathematical calculations be looked upon as absolute and final. They are all subject to the accuracy of the various assumptions, which must necessarily be made in engineering

7、work. Sometimes only a portion of the total number of parts in a machine are designed on </p><p>　　The purpose of the design calculations is, of course, to attempt to predict the stress or deformation in the

8、 part in order that it may sagely carry the loads, which will be imposed on it, and that it may last for the expected life of the machine. All calculations are, of course, dependent on the physical properties of the cons

9、truction materials as determined by laboratory tests. A rational method of design attempts to take the results of relatively simple and fundamental tests such as tension, c</p><p>　　In addition, it has been

10、amply proved that such details as surface condition, fillets, notches, manufacturing tolerances, and heat treatment have a market effect on the strength and useful life of a machine part. The design and drafting departme

11、nts must specify completely all such particulars, must specify completely all such particulars, and thus exercise the necessary close control over the finished product.</p><p>　　As mentioned above, machine d

12、esign is a vast field of engineering technology. As such, it begins with the conception of an idea and follows through the various phases of design analysis, manufacturing, marketing and consumerism. The following is a l

13、ist of the major areas of consideration in the general field of machine design:</p><p>　　① Initial design conception; </p><p>　?、?Strength analysis;</p><p>　　③ Materials selection;&

14、lt;/p><p>　　④ Appearance;</p><p>　?、?Manufacturing;</p><p><b>　?、?Safety;</b></p><p>　　⑦ Environment effects;</p><p>　?、?Reliability and life;<

15、/p><p>　　Strength is a measure of the ability to resist, without fails, forces which cause stresses and strains. The forces may be;</p><p>　?、?Gradually applied;</p><p>　　② Suddenly ap

16、plied;</p><p>　?、?Applied under impact;</p><p>　?、?Applied with continuous direction reversals;</p><p>　　⑤ Applied at low or elevated temperatures.</p><p>　　If a critic

17、al part of a machine fails, the whole machine must be shut down until a repair is made. Thus, when designing a new machine, it is extremely important that critical parts be made strong enough to prevent failure. The desi

18、gner should determine as precisely as possible the nature, magnitude, direction and point of application of all forces. Machine design is mot, however, an exact science and it is, therefore, rarely possible to determine

19、exactly all the applied forces. In addition, diff</p><p>　　Moreover, it is absolutely essential that a design engineer knows how and why parts fail so that reliable machines which require minimum maintenance

20、 can be designed. Sometimes, a failure can be serious, such as when a tire blows out on an automobile traveling at high speeds. On the other hand, a failure may be no more than a nuisance. An example is the loosening of

21、the radiator hose in the automobile cooling system. The consequence of this latter failure is usually the loss of some radiator cool</p><p>　　The type of load a part absorbs is just as significant as the mag

22、nitude. Generally speaking, dynamic loads with direction reversals cause greater difficulties than static loads and, therefore, fatigue strength must be considered. Another concern is whether the material is ductile or b

23、rittle. For example, brittle materials are considered to be unacceptable where fatigue is involved.</p><p>　　In general, the design engineer must consider all possible modes of failure, which include the fol

24、lowing:</p><p><b>　?、?Stress;</b></p><p>　　② Deformation;</p><p><b>　?、?Wear;</b></p><p>　?、?Corrosion;</p><p>　?、?Vibration;</p

25、><p>　?、?Environmental damage;</p><p>　　⑦ Loosening of fastening devices.</p><p>　　The part sizes and shapes selected must also take into account many dimensional factors which produce

26、 external load effects such as geometric discontinuities, residual stresses due to forming of desired contours, and the application of interference fit joint.</p><p>　　Selected from” design of machine elemen

27、ts”, 6th edition, m. f. sports, prentice-hall, inc., 1985 and “machine design”, Anthony Esposito, charles e., Merrill publishing company, 1975.</p><p>　　Mechanical properties of materials</p><p>

28、;　　The material properties can be classified into three major headings: (1) physical, (2) chemical, (3) mechanical</p><p>　　Physical properties </p><p>　　Density or specific gravity, moisture co

29、ntent, etc., can be classified under this category. </p><p>　　Chemical properties</p><p>　　Many chemical properties come under this category. These include acidity or alkalinity, react6ivity and

30、 corrosion. The most important of these is corrosion which can be explained in layman’s terms as the resistance of the material to decay while in continuous use in a particular atmosphere. </p><p>　　Mechanic

31、al properties </p><p>　　Mechanical properties include in the strength properties like tensile, compression, shear, torsion, impact, fatigue and creep. The tensile strength of a material is obtained by dividi

32、ng the maximum load, which the specimen bears by the area of cross-section of the specimen.</p><p>　　This is a curve plotted between the stress along the This is a curve plotted between the stress along th

33、e Y-axis(ordinate) and the strain along the X-axis (abscissa) in a tensile test. A material tends to change or changes its dimensions when it is loaded, depending upon the magnitude of the load. When the load is removed

34、it can be seen that the deformation disappears. For many materials this occurs op to a certain value of the stress called the elastic limit Ap. This is depicted by the straig</p><p>　　. Within the elastic ra

35、nge, the limiting value of the stress up to which the stress and strain are proportional, is called the limit of proportionality Ap. In this region, the metal obeys hookes’s law, which states that the stress is proportio

36、nal to strain in the elastic range of loading, (the material completely regains its original dimensions after the load is removed). In the actual plotting of the curve, the proportionality limit is obtained at a slightly

37、 lower value of the load than the </p><p>　　elastic limit. This may be attributed to the time-lagin the regaining of the original dimensions of the material. This effect is very frequently noticed in some no

38、n-ferrous metals.</p><p>　　Which iron and nickel exhibit clear ranges of elasticity, copper, zinc, tin, are found to be imperfectly elastic even at relatively low values low values of stresses. Actually the

39、elastic limit is distinguishable from the proportionality limit more clearly depending upon the sensitivity of the measuring instrument.</p><p>　　When the load is increased beyond the elastic limit, plastic

40、deformation starts. Simultaneously the specimen gets work-hardened. A point is reached when the deformation starts to occur more rapidly than the increasing load. This point is called they yield point Q. the metal which

41、was resisting the load till then, starts to deform somewhat rapidly, i. e., yield. The yield stress is called yield limit Ay.</p><p>　　The elongation of the specimen continues from Q to S and then to T. The

42、 stress-strain relation in this plastic flow period is indicated by the portion QRST of the curve. At the specimen breaks, and this load is called the breaking load. The value of the maximum load S divided by the origi

43、nal cross-sectional area of the specimen is referred to as the ultimate tensile strength of the metal or simply the tensile strength Au.</p><p>　　Logically speaking, once the elastic limit is exceeded, the m

44、etal should start to yield, and finally break, without any increase in the value of stress. But the curve records an increased stress even after the elastic limit is exceeded. Two reasons can be given for this behavior:&

45、lt;/p><p>　?、賂he strain hardening of the material;</p><p>　　②The diminishing cross-sectional area of the specimen, suffered on account of the plastic deformation.</p><p>　　The more pla

46、stic deformation the metal undergoes, the harder it becomes, due to work-hardening. The more the metal gets elongated the more its diameter (and hence, cross-sectional area) is decreased. This continues until the point S

47、 is reached.</p><p>　　After S, the rate at which the reduction in area takes place, exceeds the rate at which the stress increases. Strain becomes so high that the reduction in area begins to produce a local

48、ized effect at some point. This is called necking.</p><p>　　Reduction in cross-sectional area takes place very rapidly; so rapidly that the load value actually drops. This is indicated by ST. failure occurs

49、at this point T.</p><p>　　Then percentage elongation A and reduction in reduction in area W indicate the ductility or plasticity of the material:</p><p>　　A=(L-L0)/L0*100%</p><p>　　

50、W=(A0-A)/A0*100%</p><p>　　Where L0 and L are the original and the final length of the specimen; A0 and A are the original and the final cross-section area.</p><p>　　機器和機器零件的設(shè)計</p><p&g

51、t;<b>　　機器設(shè)計</b></p><p>　　機器設(shè)計為了特定的目的而發(fā)明或改進(jìn)機器的一種藝術(shù)。一般來講，機器時有多種不同的合理設(shè)計并有序裝配在一起的部件構(gòu)成的，在最初的機器設(shè)計階段，必須基本明確負(fù)載、元件的運動情況、工程材料的合理使用性能。負(fù)責(zé)新機器的設(shè)計最初的最重要的是經(jīng)濟性考慮。一般來說，選擇總成本最低的設(shè)計方案，不僅要考慮設(shè)計、制造、銷售、安裝的成本。還要考慮服務(wù)的費用，機械

52、要保證必要的安全性能和美觀的外形。制造機器的目標(biāo)不僅要追求保證只用功能的合理壽命，還要保證足夠便宜以同時保證其經(jīng)濟的可行性。負(fù)責(zé)設(shè)計機器的工程師，不僅要經(jīng)過專業(yè)的培訓(xùn)，而且必須是一個準(zhǔn)確判斷而又有豐富經(jīng)驗的人，具有一種有足夠時間從事專門的實際工作的素質(zhì)。</p><p><b>　　機器零件的設(shè)計</b></p><p>　　相同的理論或方程可應(yīng)用在一個一起的非常小的

53、零件上，也可用在一個復(fù)雜的設(shè)備的大型相似件上，既然如此，毫無疑問，數(shù)學(xué)計算是絕對的和最終的。他們都符合不同的設(shè)想，這必須由工程量決定。有時，一臺機器的零件全部計算僅僅是設(shè)計的一部分。零件的結(jié)構(gòu)和尺寸通常根據(jù)實際考慮。另一方面，如果機器和昂貴，或者質(zhì)量很重要，例如飛機，那麼每一個零件都要設(shè)計計算。</p><p>　　當(dāng)然，設(shè)計計算的目的是試圖預(yù)測零件的應(yīng)力和變形，以保證其安全的帶動負(fù)載，這是必要的，并且其也許影響

54、到機器的最終壽命。當(dāng)然，所有的計算依賴于這些結(jié)構(gòu)材料通過試驗測定的物理性能。國際上的設(shè)計方法試圖通過從一些相對簡單的而基本的實驗中得到一些結(jié)果，這些試驗，例如結(jié)構(gòu)復(fù)雜的及現(xiàn)代機械設(shè)計到的電壓、轉(zhuǎn)矩和疲勞強度。</p><p>　　另外，可以充分證明，一些細(xì)節(jié)，如表面粗糙度、圓角、開槽、制造公差和熱處理都對機械零件的強度及使用壽命有影響。設(shè)計和構(gòu)建布局要完全詳細(xì)地說明每一個細(xì)節(jié)，并且對最終產(chǎn)品進(jìn)行必要的測試。<

55、;/p><p>　　綜上所述，機械設(shè)計是一個非常寬的工程技術(shù)領(lǐng)域。例如，從設(shè)計理念到設(shè)計分析的每一個階段，制造，市場，銷售。以下是機械設(shè)計的一般領(lǐng)域應(yīng)考慮的主要方面的清單：</p><p>　?、僮畛醯脑O(shè)計理念 ②受力分析 ③材料的選擇 ④外形 </p><p>　　⑤制造 ⑥安全性 ⑦環(huán)境影響 ⑧可靠性及壽命<

56、/p><p>　　在沒有破壞的情況下，強度是抵抗引起應(yīng)力和應(yīng)變的一種量度。這些力可能是：</p><p>　?、贊u變力 ②瞬時力 ③沖擊力 ④不斷變化的力 </p><p><b>　?、轀夭?lt;/b></p><p>　　如果一個機器的關(guān)鍵件損壞，整個機器必須關(guān)閉，直到修理好為止。設(shè)計一臺新機器時，關(guān)

57、鍵件具有足夠的抵抗破壞的能力是非常重要的。設(shè)計者應(yīng)盡可能準(zhǔn)確地確定所有的性質(zhì)、大小、方向及作用點。機器設(shè)計不是這樣，但精確的科學(xué)是這樣，因此很難準(zhǔn)確地確定所有力。另外，一種特殊材料的不同樣本會顯現(xiàn)出不同的性能，像抗負(fù)載、溫度和其他外部條件。盡管如此，在機械設(shè)計中給予合理綜合的設(shè)計計算是非常有用的。</p><p>　　此外，顯而易見的是一個知道零件是如何和為什麼破壞的設(shè)計師可以設(shè)計出需要很少維修的可靠機器。有時，

58、一次失敗是嚴(yán)重的，例如高速行駛的汽車的輪胎爆裂。另一方面，失敗未必是麻煩。例如，汽車的冷卻系統(tǒng)的散熱器皮帶管松開。這種破壞的后果通常是損失一些散熱片，可以探測并改正過來。零件負(fù)載類型是一個重要的標(biāo)志。一般而言，變化的動負(fù)載比靜負(fù)載會引起更大的差異。因此，疲勞強度必須符合。另一個關(guān)心的方面是這種材料是否直或易碎。例如有疲勞破壞的地方不易使用易碎的材料。一般的，設(shè)計師要靠考慮所有破壞情況，其包括以下方面：</p><p&

59、gt;　?、賾?yīng)力 ②應(yīng)變 ③外形 ④腐蝕 ⑤震動 ⑥外部環(huán)境破壞 ⑦緊固件的松脫</p><p>　　零件的尺寸和外形的選擇也有很多因素。外部負(fù)荷的影響，如幾何間斷，由于輪廓而產(chǎn)生的殘余應(yīng)力和組合件干涉。</p><p>　　選自《機械元件設(shè)計》第六版，斯鮑特、普瑞特斯等，1985年和《機械設(shè)計》埃斯普特斯、查里斯、麥瑞歐出版公司，1975年

60、。</p><p><b>　　材料的機械性能</b></p><p>　　的機械性能可以被分成三個方面：物理性能，化學(xué)性能，機械性能。</p><p><b>　　物理性能</b></p><p>　　密度或比重、溫度等可以歸為這一類。</p><p><b>　

61、　化學(xué)性能</b></p><p>　　這一種類包括很多化學(xué)性能。其中包括酸堿性、化學(xué)反應(yīng)性、腐蝕性。其中最重要的是腐蝕性，在外行人看來，腐蝕性被解釋為在某處的零件抵抗腐蝕的能力。</p><p><b>　　機械性能</b></p><p>　　機械性能包括拉伸性能、壓縮性能、剪切性能、扭轉(zhuǎn)性能、沖擊性能、疲勞性能和蠕變。材料的拉

62、伸強度可以通過試件的橫截面積出試件承受的最大載荷得到，這是在拉伸試驗中，應(yīng)力沿Y軸，應(yīng)邊沿X軸變化的曲線。一種材料加載時開始發(fā)生變化的初值取決于負(fù)載的大小。當(dāng)負(fù)載去掉時可以看到變形消失。對于很多材料而言，在達(dá)到彈性極限的一定應(yīng)力值A(chǔ)之前，一直表現(xiàn)為這樣。在應(yīng)力--應(yīng)變圖中，這是可以用線性關(guān)系來描述的。這之后又一個小的偏移。</p><p>　　在彈性范圍內(nèi)，達(dá)到應(yīng)力的極限之前，應(yīng)力和應(yīng)變是成比例的，這被稱為比例極

63、限Ap。在這個區(qū)域，零件符合胡克定律，即應(yīng)力與應(yīng)變是成比例的，在彈性范圍內(nèi)（材料能完全恢復(fù)到最初的尺寸，當(dāng)負(fù)載去掉時）。曲線中的實際點，比例極限在彈性極限處。這可以認(rèn)為是材料恢復(fù)初值時落后于前者。這種影響在不含鐵的材料中經(jīng)常提到。</p><p>　　鐵和鎳有明顯的彈性范圍，而銅、鋅、錫等，即使在相對低的應(yīng)力下也表現(xiàn)為不完全彈性。實際上，能否清楚地分辯彈性極限和比例極限取決于測量設(shè)備的靈敏度。</p>

64、<p>　　當(dāng)負(fù)載超過彈性極限時，塑性變形開始，逐漸的試件被硬化。變形比負(fù)載增加得更快時的點被稱成為屈服點Q。金屬開始抵抗負(fù)載轉(zhuǎn)變成快速變形，這時的屈服力成為屈服極限Ay。</p><p>　　試件的延伸率 繼續(xù)由Q到T再到，在這種塑性流動時，應(yīng)力—應(yīng)變關(guān)系在曲線上處于QRST區(qū)域。在點，試件破壞且這種負(fù)載稱為破壞負(fù)載。最大負(fù)載S除以試件初始的截面積，被定義為這種金屬的最終拉伸極限或試樣的拉伸強度A

65、u。</p><p>　　按邏輯說，在應(yīng)力不增加的情況下，一旦超出彈性極限，金屬開始屈服，并最終破壞。但是當(dāng)超出彈性極限后，在紀(jì)錄曲線上應(yīng)增大。</p><p>　　這種變化主要有兩個原因：</p><p><b>　?、俨牧系膽?yīng)力硬化</b></p><p>　?、谟捎谒苄宰冃味鸬脑嚰M截面積的變小</p&g

66、t;<p>　　由于加工硬化，金屬塑性變化越大，硬化越嚴(yán)重。金屬拉伸越長，他的直徑（橫截面積）越小。直到到達(dá)點為止。點之后，減少的速率開始變化，超過了應(yīng)力增加的速率，應(yīng)變很大以至于在局部的某些點的面積減少，被稱為頸縮。橫截面積減少得非?？欤灾劣诳关?fù)載的能力下降，即ST階段。破壞發(fā)生在T點。延伸率A和截面積變化率u被描述成材料的延展性和塑性：</p><p>　　a=(L0-L)/L0*100%&l