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绿化洒水车设计(三吨载重量)管路设计和喷洒部件设计(有cad图 文献翻译).rar

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    绿化 洒水车 设计 载重量 管路 喷洒 部件 cad 图文 翻译
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    Engineering Failure Analysis 14 (2007) 895–902Failure investigation of a tie rod end of an automobilesteering systemA.H. Falah *, M.A. Alfares, A.H. ElkholyMechanical Engineering Department, Kuwait University,P.O. Box 5969, Safat 13060, KuwaitReceived 30 May 2006; accepted 19 November 2006AbstractA failure analysis of a tie rod end of a sports utility vehicle (SUV) steering mechanism has been carried out in this study. The tie rod end is composed of two parts fitted together: a threaded part and an embracing part. Failure took place in the threaded part which is made of AISI 8620 steel. The vehicle had been in service for approximately two years and accumulated less than 30,000 km. An evaluation of the failed part was undertaken to determine the cause of failure and assess its integrity. Visual examination, photo documentation, chemical analysis, hardness measurement, and metallographic examination were all conducted. The failure surface was examined with the help of a scanning electron microscope (SEM) equipped with EDAX facility that determines chemical composition at desired locations within the part. Results indicated that the tie rod end had failed by fatigue with a crack initiation at the throat (minimum) area of the threaded part due to material deficiency and improper heat treatment.Keywords: Fatigue; Crack initiation/propagation; Material property1. IntroductionTie rods connect the center link to the steering knuckle on automobiles with conventional suspension systems and recirculating ball steering gears, Fig. 1. On automobiles with MacPherson strut suspension and rack- and -pinion steering gears, tie rods connect the end of the rack to the steering knuckle, Fig. 2. A tie rod consists of an inner and an outer end as shown in both previous figures.Tie rods transmit force from the steering center link or the rack gear to the steering knuckle, causing the wheels to turn. The outer tie rod end connects with an adjusting sleeve, which allows the length of the tie rod to be adjust -able. This adjustment is used to set a vehicle’s toes, a critical alignment angle, sometimes referred to as the caster and camber angles.Fig. 1. Conventional suspension.Fig. 2. McPherson suspension with rack and pinion.A vehicle’s steering and suspension systems should be checked regularly, at least once a year along with a complete wheel alignment. A worn tie rod end, due to rubbing and wearing, can cause wandering, erratic steering and excessive tire wear. If tie rod replacement is necessary, a wheel alignment is also required because tie rod replacement disturbs the toe setting.Tie rods may fail in many different ways, and except for a slight increase in noise level and vibration, there is often no indication of difficulty until total failure occurs. In general, each type of failure leaves characteristicclues, and detailed examination often yields enough information to establish the cause of failure. The general types of tie rod failure modes include fatigue, impact fracture, wear and stress rupture [1]. Several causes of tierod end failure have been identified. These include poor design, incorrect assembly, overloads, inadvertent stress raisers or subsurface defects in critical areas, use of incorrect materials and/or manufacture process,and improper heat treatment [2]. Tie rods in automobile suspension are generally robust and reliable components .However, problems do occur particularly due to manufacture error or driver misuse [3].The case under investigation involves failure of the outer part of an automobile tie rod. It was brought for analysis by the investigation bureau of the Ministry of Interior over a legal dispute between the driver of an SUV and a local car dealer who sold him the vehicle. The vehicle was driven for nearly two years and had registered less than 30,000 km. The driver claimed that while he was driving the vehicle, a sudden bang was heard and he lost control of the vehicle and hit the median rail guard of the highway. The vehicle was damaged and the driver, though still conscious, was slightly injured. He believed that there was something went suddenly wrong with a mechanical component of the vehicle and that caused the accident. The local car dealer, on the other hand, disagreed with the driver’s scenario on grounds that the manufacturer produced thousands of such vehicles every year and they were, and still are, running fine all over the world without any reported serious failure. The dealer attributed the accident to careless driving behavior that resulted in a loss of control over the vehicle, which in turn hit the guard rail and led to vehicle damage. To settle the dispute, it was decided to undertake a thorough failure analysis investigation of all components of the steering mechanism to determine the cause of failure. All steering components were found intact though badly bent, except for the outer tie rod end which was fractured at the throated area of its threaded part. The embracing part of the outer tie rod end, however, was intact, except for two scars at its rim that could have happened when the threaded part broke into two pieces. The general appearance of the parts of the failed tie rod end is shown in Fig. 3a, where the two fragmented pieces of the threaded part were brought together to show how the tie rod end appeared before failure. Fig. 3b shows the two fractured parts separated. Fig. 4 gives the visual appearance of the embracing part and one fragment of the threaded part, both facing up. It is clear that fracture took place at the throat area of the threaded part where stress is expected to be high due to reduced cross sectional area and stress concentration. Further examination of the threaded part was conducted to determine the exact cause of failure.Fig. 3. Parts of fractured tie rod end (a) assembled and (b) separated.Fig. 4. Threaded part fracture surface and rim scars on embracing part.2. Experimental procedureThe failed threaded part of the tie rod end was inspected visually and macroscopically taking care to avoid damage of fractured surface. The failed threaded part of the tie rod end was ultrasonically cleaned prior to microscopic examination, photo documentation, chemical analysis and hardness measurement at the fracture surface and away from it. Scanning electron microscope (SEM) equipped with EDAX facility and an opticalmicroscope were both used in the investigation.3. Results and discussionChemical analysis using atomic absorption spectrophotometry was carried out at several locations of the failed threaded part of the tie rod end and the average values of the test results are given in Table 1 along with the specified chemical composition. Spectrum analysis revealed that the threaded part material was AISI 8620 steel which is usually used for main automobile steering components. The low percentage of manganese and ofchromium in the tested sample suggests that the final hardness of the part would be substantially reduced. On the other hand, the high percentage of nickel in the tested sample would result in lower toughness therebycompromising the mechanical property that is required to withstand impact loads resulting from bumpy roads. The surface hardness of the fractured tie rod end was measured to be 45.6 HRC. This suggests that the tie rod was not hardened properly, since hardness of tie rods, in general, is expected in the range of fifties for such applications. Table 1Chemical composition of failed threaded part of tie rod end and AISI 8620 steelFig. 5. SEM micrograph showing crack propagation region.It is evident from Fig. 4 that there exist two distinct areas on the fracture surface; one is smooth while the other is relatively rough. This is a typical fatigue fracture where crack originates at the edge of the smooth areaand propagates towards the rough area, which represents final failure. On the other hand, the smooth area of the fracture surface is dominant as seen in Fig. 4. This indicates that the tie rod end took some time to break from the instant of crack initiation till complete fracture; i.e. a high cycle fatigue failure case. This proves that the cause of the SUV accident was a lack of strength and low resistance to impact loads in the material of the threaded part of the tie rod end that initiated a crack and then took some time to reach complete separation.A specimen from the fractured surface was metallographically prepared and observed in a scanning electron microscope (SEM). Significant fatigue cracks were observed at the smooth area of the fracture surface. Theorigin of cracks was at the edge of the smooth area of the threaded part throat, suggesting that the stresses were highest at this region. Fig. 5 shows crack propagation on the fracture surface. Beach marks can be observed clearly which is a typical feature of fatigue failure [4].The origin of the crack was surrounded by beach marks. Also, the fracture surface at the fatigue region had a smooth appearance with a rippled beach mark pattern which indicates that fatigue had initiated at one point of the circumference and then grown across the fracture area. A small area has a rough, jagged look where the last portion of the throat broke away. No corrosion media were found on fracture surfaces. Fig. 6. SEM micrograph showing typical brittle fracture observed in final stage of crack propagation zone.Brittle fracture was observed in the final stage at crack propaga tion as seen in Fig. 6. Fig. 7 shows the micrography of the rough area of the fracture surface where variation of grain size combined with shallow dimples is evident. The light lines surrounding the grains in the figure indicate intergranular cracking that is usually observed with brittle fracture. A close-up of such grains revealed both intergranular and transgranular cracking at some locations as shown in Fig. 8.Fig. 7. SEM micrograph of the last portion of fracture surface to break away.Fig. 8. Close-up showing both intergranular and transgranular cracking.Quantitative chemical analysis was carried out by EDAX attached to SEM on the fracture surface to verify the presence of any other associated components. No presence of any detrimental foreign elements was observed.Metallographic view of a sample cut from the threaded part after polishing and etching with 2% Nital solution is shown in Fig. 9. As shown, the microstructure consists of pearlite (finger print appearance) and ferrite (which appears dark). This is typical of unhardened low carbon steel. No abnormality was observed in the microstructure.From the above observation, it can be ascertained that failure was caused by high stress concentration at the throat area mainly due to inadequate chemical composition which contributed to reduction in material strength and lack of toughness. Under the cyclic loading produced from driving the SUV on regular and bumpy roads, fatigue cracks had initiated at these stress concentration points, namely the throat, leading to fracture of the part at the instant when the local stress exceeded the material strength. It should be mentioned, as well, that every so often, the increased noise and vibration due to crack propagation go unnoticed till failure unexpectedly occurs. In order to further improve the durability of the tie rod end to stand the applied loads, it is suggested to increase the cross-sectional area of the threaded part throat and to enlarge the fillet radius.Fig. 9. Micrograph of thread part showing Pearlite (Finger prints Matrix) and a–Ferrite (sample was etched with 2% Nital).4. ConclusionThis study was conducted on a failed tie rod end of a SUV. Spectrum analysis and hardness measurement revealed that the failed part was AISI 8620 steel. The composition and hardness did not conform to the specified standard. Fractographic features indicated that fatigue was the main cause of failure of the tie rod end. On the fracture surface of the threaded part of the rod, the crack initiation region and beach marks could be clearly identified. It was observed that the fatigue crack originated from destructive areas in the vicinity of the throat and propagated from there. Failure analysis results indicate that the primary cause of failure of the tie rod was likely material deficiency. Formation of the crack initiation and propagation together with a final rupture within the fractured area supported this hypothesis and are, thus, in agreement with the claim of the SUV driver that the accident took place as a result of incompatible mechanical part, in this instance, the tie-rod end.References[1] Sheldon GL. Unusual Failure of an automobile steering component, In: Failure prevention and reliability conference, Dearborn,Mich., USA, 1983; p. 27–31.[2] Kim HR, Seo MG, Bae WB. A study of the manufacturing of tie-rod ends with casting/forging process. J Mater Processing Technol2002;125–126:471–6.[3] Sidders PA. Linked mulhead machines for operations on tie-rod ends. Mach Prod Eng 1970;30(December). p. 1054–62.[4] Fatigue and fracture. ASM handbook, Metals Park (OH): American Society for Metals, 1996, vol. 19.Engineering Failure Analysis 14 (2007) 895–902某汽车操纵系统的转向横拉杆故障研究A.H. Falah *, M.A. Alfares, A.H. ElkholyMechanical Engineering Department, Kuwait University,P.O. Box 5969, Safat 13060, Kuwait收稿日期:2006.5.30刊登日期:2006.11.19摘要:本论文对运动功能型车(SUV)转向横拉杆末端操控机制进行了故障分析,其中转向横拉杆末端由两部分组成:即螺纹连接组件和抱合杆组件。我们研究的这个SUV 是行使了大约两年,总里程 3 万公里,其螺纹组件的成分是美国钢铁学会规定的 8620 号钢,故障就是在这个地方发生的。本论文采取了多种方法对故障部分进行评测,从而确定其发生原因并评定其故障后的完整性,其中有可视化检测、图像文件系统、化学分析、硬度测试和金相检验。通过带 EDAX(能量弥散 X 线分析仪)装置的电子扫描显微镜(SEM)可以检测故障表面的任意部位的化学成分。结论指出如果螺纹组件的材料性能不好且处于不合适的热环境下,其结合处的一个初始裂缝会因疲劳效应导致转向横拉杆末端的故障。关键词:疲劳效应 初始裂缝/裂缝蔓延 材料特性1. 引言配备普通悬架系统和循环滚珠式转向装置的汽车,其转向横拉杆将中连杆和转向关节连接起来,如图1。配备MacPherson型支柱悬架系统和带齿条齿轮转向装置的汽车,其转向横拉杆将齿条和转向关节连接起来,如图2。而转向横拉杆如图1、2所示分为内端和外端。转向横拉杆将来自转向中连杆或齿条的力传向转向关节,从而使车轮转动。转向横拉杆的外端连接一个调节套以伸缩拉杆的长度,这样就可以调整汽车的车轮前端的角度,有时用来调整其转向节销的后倾角或外倾角。汽车的转向和悬挂系统应该定期地检查,一年至少进行一次全面的前轮校正。一个使用超期转向横拉杆,由于摩擦和磨损作用,会导致行车方向控制的不稳定和轮胎额外的磨损。如果需要更换转向横拉杆,那么相应地也要进行前轮校正,因为前者的更换会影响后者的定位。图1 普通悬架系统
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