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1、Failure analysis of an automobile differential pinion shaft Abstract Differential is used to decrease the speed and to provide moment increase for transmitting the movement coming from the engine to the wheels by turning it according to the suitable angle in vehicles and to provide that inner and

2、outer wheels turn differently. Pinion gear and shaft at the entrance are manufactured as a single part whereas they are in different forms according to automobile types. Mirror gear which will work with this gear should become familiar before the assembly. In case of any breakdown, they should be ch

3、anged as a pair. Generally, in these systems there are wear damages in gears. The gear inspected in this study has damage as a form of shaft fracture. In this study, failure analysis of the differential pinion shaft is carried out. Mechanical characteristics of the material are obtained first. Then

4、, the microstructure and chemical compositions are determined. Some fractographic studies are carried out to asses the fatigue and fracture conditions. Keywords: Differential; Fracture; Power transfer; Pinion shaft 1. Introduction The final-drive gears may be directly or indirectly driven from th

5、e output gearing of the gearbox. Directly driven final drives are used when the engine and transmission units are combined together to form an integral construction. Indirectly driven final drives are used at the rear of the vehicle being either sprung and attached to the body structure or unsprung

6、and incorporated in the rear-axle casing. The final-drive gears are used in the transmission system for the following reasons [1]: (a) to redirect the drive from the gearbox or propeller shaft through 90° and, (b) to provide a permanent gear reduction between the engine and the driving road-wheels

7、. In vehicles, differential is the main part which transmits the movement coming from the engine to the wheels. On a smooth road, the movement comes to both wheels evenly. The inner wheel should turn less and the outer wheel should turn more to do the turning without lateral slipping and being flun

8、g. Differential, which is generally placed in the middle part of the rear bridge, consists of pinion gear, mirror gear, differential box, two axle gear and two pinion spider gears. A schematic illustration of a differential is given in Fig. 1. The technical drawing of the fractured pinion shaft is

9、 also given in Fig. 2. Fig. 3 shows the photograph of the fractured pinion shaft and the fracture section is indicated. In differentials, mirror and pinion gear are made to get used to each other during manufacturing and the same serial number is given. Both of them are changed on condition that th

10、ere are any problems. In these systems, the common damage is the wear of gears [2–4]. In this study, the pinion shaft of the differential of a minibus has been inspected. The minibus is a diesel vehicle driven at the rear axle and has a passenger capacity of 15 people. Maximum engine power is 90/40

11、00 HP/rpm, and maximum torque is 205/1600 Nm/rpm. Its transmission box has manual system (5 forward, 1 back). The damage was caused by stopping and starting the minibus at a traffic lights. In this differential, entrance shaft which carries the pinion gear was broken. Various studies have been made

12、to determine the type and possible reasons of the damage. These are:  studies carried out to determine the material of the shaft;  studies carried out to determine the micro-structure;  studies related to the fracture surface. There is a closer photograph of the fractured surfaces and fractu

13、re area in Fig. 4. The fracture was caused by taking out circular mark gear seen in the middle of surfaces. Fig. 1. Schematic of the analysed differential. Fig. 2. Technical drawing of the analysed pinion shaft Fig. 3. The picture of the undamaged differential pinion analysed in the study

14、 Fig. 4. Photographs of failed shaft 2. Experimental procedure Specimens extracted from the shaft were subjected to various tests including hardness tests and metallographic and scanning electron microscopy as well as the determination of chemical composition. All tests were carried out at room

15、temperature. 2.1. Chemical and metallurgical analysis Chemical analysis of the fractured differential material was carried out using a spectrometer. The chemical composition of the material is given in Table 1. Chemical composition shows that the material is a low alloy carburising steel of the A

16、ISI 8620 type. Hardenability of this steel is very low because of low carbon proportion. Therefore, surface area becomes hard and highly enduring, and inner areas becomes tough by increasing carbon proportion on the surface area with cementation operation. This is the kind of steel which is general

17、ly used in mechanical parts subjected do torsion and bending. High resistance is obtained on the surface and high fatigue endurance value can be obtained with compressive residual stress by making the surface harder [5–7]. In which alloy elements distribute themselves in carbon steels depends prima

18、rily on the compound- and carbide-forming tendencies of each element. Nickel dissolves in the a ferrite of the steel since it has less tendency to form carbides than iron. Silicon combines to a limited extent with the oxygen present in the steel to form nonmetallic inclusions but otherwise dissolves

19、 in the ferrite. Most of the manganese added to carbon steels dissolves in the ferrite. Chromium, which has a somewhat stronger carbide-forming tendency than iron, partitions between the ferrite and carbide phases. The distribution of chromium depends on the amount of carbon present and if other str

20、onger carbide-forming elements such as titanium and columbium are absent. Tungsten and molybdenum combine with carbon to form carbides if there is sufficient carbon present and if other stronger carbide-forming elements such as titanium and columbium are absent. Manganese and nickel lower the eutect

21、oid temperature [8]. Preliminary micro structural examination of the failed differential material is shown in Fig. 5. It can be seen that the material has a mixed structure in which some ferrite exist probably as a result of slow cooling and high Si content. High Si content in this type of steel im

22、proves the heat treatment susceptibility as well as an improvement of yield strength and maximum stress without any reduction of ductility [9]. If the microstructure cannot be inverted to martensite by quenching, a reduction of fatigue limit is observed. Table 1 Chemical analysis of the pinion ge

23、ar material (wt%) Fe C Si Mn P S Cr Mo Ni 96.92 0.235 0.252 0.786 0.044 0.016 0.481 0.151 0.517 and fracture surfaces. Fig. 5. Micro structure of the material (200·). There are areas with carbon phase in Fig. 5(a). There is the transition boundary of carburisation in Fig. 5(b) and (c) shows the

24、 matrix region without carburisation. As far as it is seen in these photographs, the piece was first carburised, then the quenching operation was done and than tempered. This situation can be understood from blind martensite plates. 2.2. Hardness tests The hardness measurements are carried out by

25、a MetTest-HT type computer integrated hardness tester. The load is 1471 N. The medium hardness value of the interior regions is obtained as 43 HRC. Micro hardness measurements have been made to determine the chance of hardness values along the cross-section because of the hardening of surface area d

26、ue to carburisation. The results of Vickers hardness measurement under a load of 4.903 N are illustrated in Table 2. 2.3. Inspection of the fracture The direct observations of the piece with fractured surfaces and SEM analyses are given in this chapter. The crack started because of a possible prob

27、lem in the bottom of notch caused the shaft to be broken completely. The crack started on the outer part, after some time it continued beyond the centre and there was only a little part left. And this part was broken statically during sudden starting of the vehicle at the traffic lights. As a charac

28、teristic of the fatigue fracture, there are two regions in the fractured surface. These are a smooth surface created by crack propagation and a rough surface created by sudden fracture. These two regions can be seen clearly for the entire problem as in Fig. 4. The fatigue crack propagation region co

29、vers more than 80% of the cross-section. Table 2 Micro hardness values Distance from surface (lm) 50 100 200 400 Center Values HV (4903N) 588 410 293 286 263 Fig. Fig. 6. SEM image of the fracture surface showing the ductile shear. Fig. 7. SEM image of the fracture surface showing the bea

30、ch marks of the fatigue crack propagation. Shaft works under the effect of bending, torsion and axial forces which affect repeatedly depending on the usage place. There is a sharp fillet at level on the fractured section. For this reason, stress concentration factors of the area have been determine

31、d. Kt = 2.4 value (for bending and tension) and Kt = 1.9 value (for torsion) have been acquired according to calculations. These are quite high values for areas exposed to combined loading. These observations and analysis show that the piece was broken under the influence of torsion with low nomina

32、l stresses and medium stress concentration [10]. The scanning electron microscopy shows that the fracture has taken place in a ductile manner (Fig. 6). There are some shear lips in the crack propagation region which is a glue of the plastic shear deformations. Fig. 7 shows the beach marks of the fa

33、tigue crack propagation. The distance between any two lines is nearly 133 nm. 3. Conclusions A failed differential pinion shaft is analysed in this study. The pinion shaft is produced from AISI 8620 low carbon carburising steel which had a carburising, quenching and tempering heat treatment proces

34、s. Mechanical properties, micro structural properties, chemical compositions and fractographic analyses are carried out to determine the possible fracture reasons of the component. As a conclusion, the following statements can be drawn:  The fracture has taken place at a region having a high stres

35、s concentration by a fatigue procedure under a combined bending, torsion and axial stresses having highly reversible nature.  The crack of the fracture is initiated probably at a material defect region at the critical location.  The fracture is taken place in a ductile manner.  Possible later

36、failures may easily be prevented by reducing the stress concentration at the critical location. Acknowledgement The author is very indebted to Prof. S. Tasgetiren for his advice and recommendations during the study. H. Bayrakceken / Engineering Failure Analysis 13 (2006) 1422–1428 References [1

37、] Heisler H. Vehicle and engine technology. 2nd ed. London: SAE International; 1999. [2] Makevet E, Roman I. Failure analysis of a final drive transmission in off-road vehicles. Eng Failure Anal 2002;9:579–92. [3] Orhan S, Aktu¨rk N. Determination of physical faults in gearbox through vibration an

38、alysis. J Fac Eng Arch Gazi University 2003;18(3):97–106. [4] Tasgetiren S, Aslantas K, Ucun I. Effect of press-fitting pressure on the fatigue damages of root in spur gears. Technol Res: EJMT 2004;2:21–9. [5] Nanawarea GK, Pableb MJ. Failures of rear axle shafts of 575 DI tractors. Eng Failur

39、e Anal 2003;10:719–24. [6] Aslantas K, Tasgetiren S. A study of spur gear pitting formation and life prediction. Wear 2004;257:1167–75. [7] Savas V, O¨ zek C. Investigation of the distribution of temperature on a shaft with respect to the deflection. Technol Res: EJMT 2005;1:33–8. [8] Smith F

40、W. Principles of materials science and engineering. 3rd ed. USA: McGraw-Hill Series; 1996. p. 517–18. [9] ASM metal handbook, vol. 1. Properties and selection, irons, steels, and high performance alloys; 1991. [10] Voort GFV. Visual examination and light microscopy. ASM handbook metallography and

41、microstructures. Materials Park (OH): ASM International; 1991. p. 100–65. 汽車差速器小齒輪軸的失效分析 摘要 差速器的作用是根據(jù)車輛合適的角度, 通過將運動轉(zhuǎn)向, 為運動傳輸減速或者提供瞬間加速, 這個運動來自引擎, 到車輪去, 使內(nèi)外車輪轉(zhuǎn)動不同。開口處的游星齒輪和輪軸是作為單一零件的，但是根據(jù)車輛型號有不同的形狀。和這個齒輪一起工作的鏡面齒輪應(yīng)該在組裝前就磨合好。一旦發(fā)生故障，它們應(yīng)該成對更換。一般來說，在這些系統(tǒng)中齒輪都存在磨損損壞。本文中檢查的齒輪損壞具體說是輪軸斷裂。 本研究進(jìn)行了

42、差速器小齒輪軸的失效分析。首先，取得材料的機(jī)械特點，然后確定其微觀結(jié)構(gòu)和化學(xué)成分，還要做一些顯微鏡觀察研究來評估其疲勞和破損狀況。 關(guān)鍵詞：差速器; 破損；動力分配裝置；小齒輪軸 簡介 最終傳動齒輪可能直接或間接地由齒輪箱的輸出齒輪驅(qū)動。當(dāng)引擎和傳輸設(shè)備結(jié)合在一起，形成統(tǒng)一結(jié)構(gòu)時，就需要使用直接驅(qū)動的最終傳動齒輪。間接驅(qū)動最終傳動齒輪或者借助一些裝置附在汽車后端，或者并入后橋殼。最終驅(qū)動齒輪由于如下原因被使用在傳輸系統(tǒng)中： (a)為了使齒輪箱或者傳動軸的動力90°轉(zhuǎn)向 (b)為了提供引擎和驅(qū)動輪之間永久的齒輪減速。 在汽車中，差速器是將運動從引擎?zhèn)鬏數(shù)杰囕喌闹饕考?。在平坦的道路?/p>

43、，運動會平均分配給兩個輪子。內(nèi)側(cè)車輪應(yīng)該程度小一些, 外側(cè)車輪轉(zhuǎn)向程度應(yīng)該大一些, 這樣轉(zhuǎn)彎才不會側(cè)滑。差速器通常置于后橋中部，由游星齒輪、鏡面齒輪、差速器箱、軸齒輪和兩個游星蜘蛛齒輪構(gòu)成。 圖表一是差速器的示意圖，圖表二是斷裂的小齒輪軸的技術(shù)圖解，圖表三是斷裂的小齒輪軸的圖片，表示出了斷裂部分。 在差速器里，人們生產(chǎn)時將鏡面和流星齒輪制作得相互適應(yīng)，并且使用相同的序列號。出現(xiàn)問題的話，二者都要更換。在這些系統(tǒng)中，常見的損傷是齒輪磨損。本研究檢查了一輛小型巴士的差速器小齒輪軸。該小型巴士是后軸驅(qū)動的柴油汽車，可搭載15名乘客。發(fā)動機(jī)最大功率是 ，最大扭轉(zhuǎn)力是 。傳動箱里有手動

44、系統(tǒng) (5個向前，一個向后)。損傷是由巴士在交通燈出停止和啟動引起的。在差速器中，驅(qū)動流星齒輪的輸入軸斷裂。人們做了各種各樣的研究來確定這種損傷的類型和可能的原因。 它們是: 確定輪軸材料的研究 確定微觀結(jié)構(gòu)的研究 與斷裂面相關(guān)的研究 圖四是斷裂表面和斷裂區(qū)域的近距離照片。這個斷裂是將表面中心的圓形標(biāo)記齒輪取走形成的。 鏡面齒輪 行星齒輪 齒輪軸 十字銷 太陽輪 半軸 圖1 進(jìn)行分析的差速器的圖解 圖2 進(jìn)行分析的小齒輪軸的技術(shù)圖解 失效十字部分 圖3 研究中進(jìn)行分析的完好小齒輪軸的圖片 靜態(tài)斷裂區(qū)域 裂紋擴(kuò)展區(qū)域 圖4 失效輪軸

45、的照片 實驗步驟 從輪軸中取得的樣本要接受各種各樣的測試，包括硬度測試，金相和掃描電子顯微鏡以及化學(xué)成分的確定。左右測試均在室溫下進(jìn)行。 化學(xué)和冶金分析 斷裂差速器材料的化學(xué)分析是使用光譜儀完成的。該材料的化學(xué)成分如表一所示?；瘜W(xué)成分顯示該材料是美國鋼鐵協(xié)會8620型的一種低合金碳化鋼。這種鋼的淬硬性很低，因為碳含量比例較低。因而，需要通過滲碳處理增加表面區(qū)域的碳比例，使表面區(qū)域變得堅硬，非常耐用，內(nèi)部區(qū)域變得堅韌。這種鋼一般用在需要扭轉(zhuǎn)和彎曲的機(jī)械部件中。通過使表面變硬，用殘余應(yīng)力使表面獲得高阻力性，獲得高疲勞承受值。 合金元素怎樣摻入碳鋼主要取決于每種元素的化合傾向和形成碳化物的

46、傾向。鎳溶解于鋼的鐵酸鹽，因為它比鐵更不容易形成碳化物。硅與鋼中的氧在一定程度上結(jié)合形成非金屬內(nèi)含物，不然的話則溶于鐵酸鹽。鉻比鐵更容易形成碳化物一些，會在鐵酸鹽和碳化物階段之間分解。摻入鉻取決于碳含量以及是否沒有鈦、鈳這樣更易形成碳化物的元素存在。如果有足夠的碳并且沒有鈦、鈳這樣更易形成碳化物的元素存在，鎢和鉬可以和碳形成碳化物。錳和鎳可以降低共析混合物的溫度。 失效差速器材料的初步微觀檢驗如圖五所示?？梢钥闯鲞@種材料有一種復(fù)合結(jié)構(gòu)，由于緩慢冷卻和較高的硅含量，該結(jié)構(gòu)中很可能存在鐵酸鹽。這種鋼中的高硅含量可以提高受熱敏感性還有提高屈服強(qiáng)度和最大壓力，而不降低延展性。如果微觀結(jié)構(gòu)不能通過冷淬

47、轉(zhuǎn)化為馬氏體, 就可以觀察到疲勞極限降低。 表1 流星齒輪材料的化學(xué)分析 擴(kuò)散區(qū)域 過渡區(qū)域 滲碳區(qū)域 圖5 該材料的微觀結(jié)構(gòu) 圖5（a）中有處于碳階段的區(qū)域。圖五(b)中有滲碳的過渡邊緣，(c)顯示了未滲碳的基質(zhì)區(qū)域，而后進(jìn)行冷淬操作，接著再回火。這種情形可以從不易觀察到的馬氏體片來理解。 2．2 硬度測試 硬度測試時通過MetTest-HT型計算機(jī)集成硬度測試器進(jìn)行的。其負(fù)荷為14N。內(nèi)部區(qū)域的平均硬度值為43HRC，并進(jìn)行了微觀硬度測試，以確定滲碳引起的表面的硬化帶來的橫截面硬度值的變化。在4.903N的負(fù)荷量下，維式硬度計硬度測試的結(jié)果如表2所示。 2.3

48、斷裂處的檢查 本章給出了表面斷裂的輪軸的直接觀察結(jié)果和掃描式電子顯微鏡分析結(jié)果。刻痕底部可能的問題導(dǎo)致出現(xiàn)裂縫，使整個輪軸完全斷裂。裂縫在外部開始，過一段時間斷裂范圍越過中心部分，只剩一小部分沒有斷裂。而這一部分也會在車輛在交通燈處突然啟動時靜止斷裂。在斷裂表面有兩個區(qū)域，這是疲勞斷裂的一個特點。有一個裂縫擴(kuò)大引起的光滑表面和一個突然斷裂引起的粗糙表面。這兩個區(qū)域可以在圖4的問題中清楚地看到。疲勞裂縫擴(kuò)大區(qū)域占橫截面的80%。 表2 微觀硬度值 圖6 顯示出斷裂表面韌性剪切帶的掃描式電子顯微鏡圖像 圖7 顯示疲勞裂縫擴(kuò)散海灘紋的斷裂表面的掃描電子顯微鏡圖像 輪軸在彎曲、

49、扭轉(zhuǎn)、軸向力的作用下工作，彎曲、扭轉(zhuǎn)、軸線力不斷影響依賴使用區(qū)域。在斷裂部分有一個鋒利的薄片, 這樣就可以確定該區(qū)域的壓力集中因素。根據(jù)計算，得知彎曲和壓力的Kt值為2.4，扭轉(zhuǎn)的Kt值為1.9。對于承受組合負(fù)荷的區(qū)域這些數(shù)值是相當(dāng)高的。 這些觀察和分析顯示，輪軸在很少壓力，中等壓力集中的情況下，受扭轉(zhuǎn)影響而斷裂。 掃描電子顯微鏡顯示，斷裂是延展的狀態(tài)下發(fā)生的（圖6）。在裂縫擴(kuò)散區(qū)域有一些切變裂痕，切變裂痕總是伴隨切變形發(fā)生。圖7 顯示了疲勞裂縫擴(kuò)散的海灘紋。任何兩條紋之間都在133納米左右。 3.結(jié)論 本文分析了失效的差速器小齒輪軸。小齒輪軸是用美國鋼鐵協(xié)會8620低碳滲碳鋼生產(chǎn)的，

50、這種鋼經(jīng)過滲碳、冷淬和回火熱處理過程。進(jìn)行了機(jī)械性質(zhì)、微觀結(jié)構(gòu)性質(zhì)、化學(xué)成分和金屬斷面的顯微鏡觀察分析，以確定小齒輪軸可能的斷裂原因。 可以得出以下結(jié)論： 1、 斷裂發(fā)生在有高壓力集中的區(qū)域，這些高壓力集中是由彎曲、扭轉(zhuǎn)以及高度 2、 可反轉(zhuǎn)軸向力共同作用下的疲勞過程引起的。 3、 斷裂的裂縫很有可能是關(guān)鍵位置的材料瑕疵部位開始的。 4、斷裂是在延展?fàn)顟B(tài)下發(fā)生的。 5、減少關(guān)鍵位置的壓力集中可能很容易的避免之后可能的失效。 Acknowledgement The author is very indebted to Prof. S. Tasgetiren for his advi

51、ce and recommendations during the study. H. Bayrakceken / Engineering Failure Analysis 13 (2006) 1422–1428 References [1] Heisler H. Vehicle and engine technology. 2nd ed. London: SAE International; 1999. [2] Makevet E, Roman I. Failure analysis of a final drive transmission in off-road vehicles

52、. Eng Failure Anal 2002;9:579–92. [3] Orhan S, Aktu¨rk N. Determination of physical faults in gearbox through vibration analysis. J Fac Eng Arch Gazi University 2003;18(3):97–106. [4] Tasgetiren S, Aslantas K, Ucun I. Effect of press-fitting pressure on the fatigue damages of root in spur gears

53、. Technol Res: EJMT 2004;2:21–9. [5] Nanawarea GK, Pableb MJ. Failures of rear axle shafts of 575 DI tractors. Eng Failure Anal 2003;10:719–24. [6] Aslantas K, Tasgetiren S. A study of spur gear pitting formation and life prediction. Wear 2004;257:1167–75. [7] Savas V, O¨ zek C. Investigation

54、 of the distribution of temperature on a shaft with respect to the deflection. Technol Res: EJMT 2005;1:33–8. [8] Smith FW. Principles of materials science and engineering. 3rd ed. USA: McGraw-Hill Series; 1996. p. 517–18. [9] ASM metal handbook, vol. 1. Properties and selection, irons, steels, and high performance alloys; 1991. [10] Voort GFV. Visual examination and light microscopy. ASM handbook metallography and microstructures. Materials Park (OH): ASM International; 1991. p. 100–65.