機(jī)械專業(yè)外文翻譯---殘余應(yīng)力

1、<p><b>　　附錄</b></p><p>　　Residual Stresses</p><p>　　A residual stress is one that exists without external loading or internal temperature differences on a structure or machine.

2、 It is usually a result of manufacturing or assembling operations. Sometimes it is called initial stress, and the operations, prestressing. When the structure or machine is put into service, the service loads superimpose

3、 stresses. If the residual stresses add to the service-load stresses, they are detrimental; if they subtract from the service-load stresses they are benefi</p><p>　　In the plastic deformation the external fo

4、rce does the merit turns into outside the heat except the majority of extensions, but also some small part by the distortion can the form stores up in the deformation material. This part of energy named storage energy. T

5、he storage can the concrete manifestation way is: Macroscopic residual stress, microscopic residual stress and lattice distortion. According to the residual stress balance scope difference, usually may divide into it thr

6、ee kinds: </p><p>　　(1) First kind of internal stress, also called the macroscopic residual stress, it is causes by the work piece different part macroscopic distortion nonuniformity, therefore its stress

7、balance scope including entire work piece. For example, serves with Jin Shubang the curving load, then above is pulled elongates, under receives the compression; The distortion surpasses when the limit of elasticity has

8、had the plastic deformation, after then the external force elimination by elongated one side on</p><p>　　(2) Second kind of internal stress, also called the microscopic residual stress, it is produces by bet

9、ween the crystal grain or the subgrain distortion nonuniformity. Its sphere of action and the crystal grain size quite, namely maintain the balance between the crystal grain or the subgrain. Sometimes this kind of intern

10、al stress may achieve the very great value, even possibly creates the micro crack and causes the work piece destruction. </p><p>　　(3) Third kind of internal stress, also calls the lattice distortion. Its s

11、phere of action is several dozens to several hundred nanometers, it is because the work piece forms in the plastic deformation the massive lattice flaw (for example vacancy, interstitial atom, dislocation and so on) caus

12、e. In the distortion metal the storage can the major part (80%~90%) uses in forming the lattice distortion. This part of energy enhanced the distortion crystal energy, causes it to be at the thermodynamics</p><

13、;p>　　Only a few examples of detrimental residual stresses will be given here .One, in the assembly of machinery, occurs when two shafts are not in line or are a few thousandths of an inch out of parallel, and they are

14、 forced into connection by rigid couplings. The resulting stresses in the shafts become reversing stresses when the shafts are rotated. The correction, when perfect alignment cannot be economically attained, as is freque

15、ntly the case, is to use flexible couplings of a type necessary for </p><p>　　The preceding case occurs with elastic stresses only, and the residual stresses are maintained by bearing constraints. In applica

16、tions where mechanical work causes plastic yielding .stresses remain when the constraints are removed. For example, the forging of shafts and crankshafts and the cooling after forging may induce residual stresses, the eq

17、uilibrium of which id changed in machining, causing some warping of the shafts. It is then common practice to straighten the shafts in a press before t</p><p>　　Detrimental residual stresses commonly result

18、from differential heating or cooling. A weld is a common example, The weld metal and the areas immediately adjacent are, after solidification, at a much higher temperature than the main body of metal. The natural contrac

19、tion of the metal along the length of the weld is partially prevented by the large adjacent body of cold metal. Hence residual tensile stresses are set up along the weld.</p><p>　　In general, local or shallo

20、w heating which would expand the region or surface, if it were free, a distance well beyond that which the adjacent larger volume will allow causes yielding and upsetting of the heated material, This readily occurs becau

21、se of the reduced yield strength at elevated temperatures. The same cooler volume prevents the upset, heated region from fully contracting during its cooling, and tensile general rule is that the “l(fā)ast to cool is in tens

22、ion,” although there is an except</p><p>　　A thin but highly effective surface layer of compressive stress may be induced by cold-rolling, coining, and peening processes. It is seen that these processes work

23、-harden an outer layer, thus causing compressive stresses to remain, together with minor tensile stresses in adjacent interior layers. Since the compressive layer is readily obtained all around, these processes are suita

24、ble for reversing loads and rotating components where the stress varies between tension and compression. The process</p><p>　　Cold-rolling is applied primarily to cylindrical and other shapes that can be rot

25、ated, such as threads and shaft fillets. The shape, size, and pressure of the roller and the yield strength of the shaft determine the depth of penetration, which can be calculated. A special fixture may be attached to t

26、he carriages of a lathe and made to slowly traverse the desired rolling of bolts and screws has long been part of a forming process that not only forms but strengthens the threads by deformation and </p><p>

27、　　Coining of holes, also called ball drifting, is a manufacturing process of forcing a hard, tungsten carbide or AIDI 52100 steel, slightly oversize ball through a hole in a plate, bushing, or tubing to give the holes fi

28、nal size and a fine finish. The length of the hole may be from 1/20 to 10 times its diameter. The machine is often set up for a high production of small parts with unskilled labor. An incidental result is that the proces

29、s increases hardness, hence wear resistance, and induces aroun</p><p>　　Peening is the most widely used method for prestressing by mechanically induced yielding. By the impact of rounded striking objects, th

30、e surface is deformed in a multitude of shallow dimples, which in trying to expand put the surface under compression. Hammer peening, usually by air-driven tool with a rounded end, is useful on limited areas, such as a w

31、eld in shaft or on areas found weakened by corrosion, decarburization, or minor fatigue damage. With a hard spherical end to the tool, the depth </p><p>　　Shot peening is done on steels by the high-velocity

32、impingement of small, round, steel or chilled cast-iron shot with diameters from 0.007to 0.175 in.. The compressed layer has a depth from a few thousandths to a few hundredths of an inch, less than with hammer peening, b

33、ut roughly proportioned to the shot size used and its velocity. Again the residual stress produced is about half of the strain-hardened yield strength.</p><p>　　Shot peening is extensively used because it ma

34、y be applied with minimum cost to most metals and shapes, except some interior ones. On soft metals, glass beads may be used. Helical springs are commonly shot peened, with up to a 60%increase in allowable stress under p

35、ulsating loads. Part of the improvement may be due to the removal of the weakening longitudinal scratches left from the wire-drawing operation.</p><p>　　Similarly, coarse-machined and coarse-ground surfaces

36、are smoothed and improved by shot peening, which may be a more economical method than producing a final finish by machining or grinding. Peening is not used on bearing and other closely fitting surfaces where high precis

37、ion is required. A final grinding for accuracy after peening would remove part or all of the residual stress. Machines are available for the automatic and continuous peening of small-and medium-size parts moving on a con

38、veyor </p><p><b>　　殘余應(yīng)力</b></p><p>　　殘余應(yīng)力是結(jié)構(gòu)或者機(jī)器中在沒有外部載荷或者內(nèi)部溫差時(shí)存在的一種應(yīng)力，它通常是在制造或者裝配過程中所產(chǎn)生的。有時(shí)它被稱為初始應(yīng)力，而這個(gè)過程則被成為施加預(yù)應(yīng)力。當(dāng)這些結(jié)構(gòu)或者機(jī)器投入使用時(shí)，工作載荷就會(huì)與殘余應(yīng)力相疊加。如果參與應(yīng)力相加，則這種殘余應(yīng)力是有害的；如果殘余應(yīng)力與工作應(yīng)力相減，則

39、這種殘余應(yīng)力是有利的。</p><p>　　塑性變形中外力所作的功除大部分轉(zhuǎn)化成熱之外，還有一小部分以畸變能的形式儲(chǔ)存在形變材料內(nèi)部。這部分能量叫做儲(chǔ)存能。儲(chǔ)存能的具體表現(xiàn)方式為：宏觀殘余應(yīng)力、微觀殘余應(yīng)力及點(diǎn)陣畸變。按照殘余應(yīng)力平衡范圍的不同，通常可將其分為三種： </p><p>　?。?）第一類內(nèi)應(yīng)力，又稱宏觀殘余應(yīng)力，它是由工件不同部分的宏觀變形不均勻性引起的，故其應(yīng)力平衡范圍包括

40、整個(gè)工件。例如，將金屬棒施以彎曲載荷，則上邊受拉而伸長，下邊受到壓縮；變形超過彈性極限產(chǎn)生了塑性變形時(shí)，則外力去除后被伸長的一邊就存在壓應(yīng)力，短邊為張應(yīng)力。這類殘余應(yīng)力所對(duì)應(yīng)的畸變能不大，僅占總儲(chǔ)存能的0.1％左右。 </p><p>　　（2）第二類內(nèi)應(yīng)力，又稱微觀殘余應(yīng)力，它是由晶粒或亞晶粒之間的變形不均勻性產(chǎn)生的。其作用范圍與晶粒尺寸相當(dāng)，即在晶粒或亞晶粒之間保持平衡。這種內(nèi)應(yīng)力有時(shí)可達(dá)到很大的數(shù)值，甚至可

41、能造成顯微裂紋并導(dǎo)致工件破壞。 </p><p>　?。?）第三類內(nèi)應(yīng)力，又稱點(diǎn)陣畸變。其作用范圍是幾十至幾百納米，它是由于工件在塑性變形中形成的大量點(diǎn)陣缺陷（如空位、間隙原子、位錯(cuò)等）引起的。變形金屬中儲(chǔ)存能的絕大部分（80％~90％）用于形成點(diǎn)陣畸變。這部分能量提高了變形晶體的能量，使之處于熱力學(xué)不穩(wěn)定狀態(tài)，故它有一種使變形金屬重新恢復(fù)到自由焓最低的穩(wěn)定結(jié)構(gòu)狀態(tài)的自發(fā)趨勢(shì)，并導(dǎo)致塑性變形金屬在加熱時(shí)的回復(fù)及再

42、結(jié)晶過程。</p><p>　　這里僅列舉幾個(gè)有害的殘余應(yīng)力的例子，在機(jī)器的裝配過程中，當(dāng)兩軸不在一條直線上或者在平行度上相差千分之幾英寸時(shí)，采用剛性聯(lián)軸器強(qiáng)使他們聯(lián)接在一起。當(dāng)軸旋轉(zhuǎn)時(shí)，軸上所產(chǎn)生的應(yīng)力就是一個(gè)方向不斷改變的應(yīng)力。在通常情況下無法經(jīng)濟(jì)地實(shí)現(xiàn)兩軸線之間的精確找正對(duì)準(zhǔn)時(shí)，補(bǔ)救的方法是采用能夠補(bǔ)償一定找正誤差的彈性連軸器。</p><p>　　出現(xiàn)上述情況時(shí)僅產(chǎn)生彈性應(yīng)力，而殘

43、余應(yīng)力是由于受到軸承約束而得以保存的。在機(jī)械加工造成塑性屈服的操作中，當(dāng)約束去掉后，仍然留有應(yīng)力。例如，在軸和曲軸的鍛造及隨后的冷卻過程中可能會(huì)產(chǎn)生殘余應(yīng)力，切削加工會(huì)改變其平衡狀態(tài)，使軸產(chǎn)生某種程度的翹曲。因此，通常的作法是在進(jìn)行最終的切削加工之前，在壓床上將軸矯直。矯直時(shí)需要采用足以使軸產(chǎn)生永久性變形或者屈服的彎矩。</p><p>　　不均勻加熱或者冷卻通常會(huì)產(chǎn)生殘余應(yīng)力。焊縫是一個(gè)最常見的例子。在焊縫凝固

44、后，焊縫金屬和鄰近區(qū)域的溫度要比金屬主體的溫度高的多。金屬沿著焊縫長度的自然收縮將被鄰近的體積較大、溫度較低的金屬限制了一部分。因此沿著焊縫產(chǎn)生了殘余拉應(yīng)力。</p><p>　　通常，局部或淺表面加熱會(huì)使受熱部分和表面膨脹。如果膨脹部分能夠自由移動(dòng)，其移動(dòng)距離會(huì)大大超過鄰近的較大體積的材料的移動(dòng)距離，造成了受熱材料的屈服和變厚。由于在高溫時(shí)屈服強(qiáng)度會(huì)降低，因此，這種現(xiàn)象很容易出現(xiàn)。在冷卻過程中，溫度降低的相同體

45、積的材料能夠阻止受熱變厚區(qū)域完全收縮，結(jié)果產(chǎn)生了拉應(yīng)力。因此，火焰切割后的表面處于受拉狀態(tài)，其強(qiáng)度降低。一般規(guī)律是“最后冷卻的部位處于受拉狀態(tài)”，但是如果顯微組織發(fā)生某種變化就會(huì)出現(xiàn)例外的情況。將這些殘余拉應(yīng)力減至最小或者使之反向的方法有：通過退火消除應(yīng)力，對(duì)強(qiáng)度降低的表面進(jìn)行垂擊或噴丸處理。在退火過程中，要求把低碳鋼加熱到1100~1200F，某些合金鋼要加熱到1600F，然后對(duì)每英寸厚度保溫一小時(shí)，隨后進(jìn)行緩慢冷卻。對(duì)被聯(lián)接零件進(jìn)行

46、某些預(yù)熱可以將焊縫中的拉應(yīng)力降至最低。</p><p>　　冷壓、擠壓和噴丸強(qiáng)化都會(huì)產(chǎn)生一層薄的，但是十分有效的壓應(yīng)力表面層?？梢娍闯觯@些工藝方法使工件外層產(chǎn)生加工硬化，從而產(chǎn)生壓應(yīng)力，同時(shí)在與之相鄰的內(nèi)層中產(chǎn)生較小的拉應(yīng)力。由于在各處都很容易獲得壓應(yīng)力層，因此這些工藝方法適用于交變載荷和應(yīng)力在拉應(yīng)力與壓應(yīng)力之間變化的回轉(zhuǎn)類零件。在采用這些工藝方法時(shí)，必須認(rèn)真地控制滾輪的壓力和進(jìn)給量、噴丸的大小和速度等。對(duì)于這

47、些，在工程技術(shù)書籍和期刊中有大量資料可供參考。</p><p>　　冷壓主要用于圓柱形和其他回轉(zhuǎn)類的形狀，諸如螺紋和軸的圓角。滾輪的形狀、尺寸和壓力以及軸的屈服強(qiáng)度決定著穿透深度，這是可以通過計(jì)算得到的。一種專用的夾具可以裝在車床的溜板上，使其在軸的預(yù)定長度范圍內(nèi)緩慢地往復(fù)運(yùn)動(dòng)，與之同時(shí)軸由床頭箱帶動(dòng)著旋轉(zhuǎn)。采用滾絲法加工螺栓和螺釘上的螺紋早就已經(jīng)成為一種成形加工方法。這種方法不僅能夠生成螺紋，而且還能通過螺紋根

48、部附近的變形和晶粒流動(dòng)以及產(chǎn)生的殘余壓應(yīng)力來增加螺紋的強(qiáng)度。</p><p>　　孔的擠壓，又可以稱為鋼球漲孔，這種加工方法上迫使一個(gè)尺寸稍大的堅(jiān)硬的碳化鎢或AISI52100 鋼球通過板、套筒或者管子上的孔獲得最終尺寸和較高的光潔度。孔的長度可以等于其直徑的0.05~10倍。擠壓漲孔機(jī)通常由非熟練工人操作，使用于小型零件的大量生產(chǎn)。這種方法能夠提高硬度，因此能提高耐磨性，并且在孔的周圍產(chǎn)生殘余壓應(yīng)力，這種殘余壓

49、應(yīng)力通常是有利的。例如在滾子鏈的鉸鏈中，鉸鏈承受很高的脈動(dòng)拉應(yīng)力，而且在孔表面上和表面附近有應(yīng)力集中。采用鋼球擠壓和漲孔可以產(chǎn)生壓應(yīng)力，這會(huì)降低工作中的凈拉應(yīng)力，將斷裂事故減到最低限度。</p><p>　　噴丸強(qiáng)化是通過采用機(jī)械方式引起工件表面屈服而施加預(yù)應(yīng)力的最常用的方法。在圓形打擊物的沖擊下，表面發(fā)生變形并形成許多淺坑，由于這些淺坑有向外擴(kuò)展的趨勢(shì)而使表面受壓。錘擊強(qiáng)化通常采用氣動(dòng)圓頭工具進(jìn)行，這種方法可以

50、用于較小的區(qū)域。采用硬的球頭工具時(shí)，受壓層深度可達(dá)0.3英寸左右，與表面凹坑的直徑大致相等。最大殘余應(yīng)力出現(xiàn)在表面以下，其大小約為應(yīng)變硬化區(qū)屈服強(qiáng)度的一半。</p><p>　　噴丸強(qiáng)化時(shí)，以直徑為0.007~0.175英寸的小圓鋼丸或者冷硬鑄鐵丸高速?zèng)_擊鋼制零件。受壓層的深度從千分之幾英寸到百分之幾英寸，小于錘擊強(qiáng)化時(shí)受壓層的深度，大致與所用球丸的直徑和速度成正比。所產(chǎn)生的殘余應(yīng)力也大約等于應(yīng)變強(qiáng)化區(qū)的屈服強(qiáng)度

51、的一半。</p><p>　　除了零件的某些內(nèi)部形狀外，噴丸強(qiáng)化可以用于大多數(shù)金屬和形狀，而且成本最低，因此噴丸強(qiáng)化得到了廣泛的應(yīng)用。對(duì)于軟金屬，可以采用玻璃球。螺旋彈簧通常要進(jìn)行噴丸硬化，可以使其在脈動(dòng)載荷作用下的許用應(yīng)力提高60%。強(qiáng)度增加的原因之一可能是由于消除了拔絲時(shí)產(chǎn)生的能夠起減低強(qiáng)度作用的縱向擦痕所致。同樣，進(jìn)行噴丸強(qiáng)化可以改善初加工表面和初磨表面的 質(zhì)量，使其變的光滑，這種方法可能比采用切削加工或者