1、毕业设计英文科技文献翻译附录一 英文科技文献翻译英文原文：Experimental investigation of laser surface textured parallel thrust bearingsPerformance enhancements by laser surface texturing (LST) of parallel-thrust bearings is experimentally investigated. Testresults are compared with a theoretical model and good correlation is fo
2、und over the relevant operating conditions. A compari-son of the performance of unidirectional and bi-directional partial-LST bearings with that of a baseline, untextured bearing ispresented showing the benets of LST in terms of increased clearance and reduced friction.KEY WORDS: uid lm bearings, sl
3、ider bearings, surface texturing1. IntroductionThe classical theory of hydrodynamic lubrication yields linear (Couette) velocity distribution with zero pressure gradients between smooth parallel surfaces under steady-state sliding. This results in an unstable hydrodynamic lm that would collapse unde
4、r any external force acting normal to the surfaces. However, experience shows that stable lubricating lms can develop between parallel sliding surfaces, generallybecause of some mechanism that relaxes one or more of the assumptions of the classical theory.A stable uid lm with sucient load-carrying c
5、apacity in parallel sliding surfaces can be obtained, for example, with macro or micro surface structure of dierent types. These include waviness 1 and protruding microasperities 24. A good literature review on the subject can be found in Ref. 5. More recently, laser surface texturing (LST) 68, as w
6、ell as inlet roughening by longitudinal or transverse grooves 9 were suggested to provide load capacity in parallel sliding. The inlet roughness concept of Tonder 9 is based on eective clearance reduction in the slidingdirection and in this respect it is identical to the par- tial-LST concept descri
7、bed in ref. 10 for generating hydrostatic eect in high-pressure mechanical seals.Very recently Wang et al. 11 demonstrated experimentally a doubling of the load-carrying capacity for the surface- texture design by reactive ion etching of SiC parallel-thrust bearings sliding in water. These simple pa
8、rallel thrust bearings are usually found in seal-less pumps where the pumped uid is used as the lubricant for the bearings. Due to the parallel sliding their performance is poorer than more sophisticated tapered or stepped bearings. Brizmer et al. 12 demon-strated the potential of laser surface text
9、uring in the form of regular micro-dimples for providing load-carrying capacity with parallel-thrust bearings. A model of a textured parallel slider was developed and the eect of surface texturing on load-carrying capacitywas analyzed. The optimum parameters of the dimples were found in order to obt
10、ain maximum load-carrying capacity. A micro-dimple collective eect was identi-ed that is capable of generating substantial load-carrying capacity, approaching that of optimumconventional thrust bearings. The purpose of the present paper is to investigate experimentally the validity of the model desc
11、ribed in Ref. 12 by testing practical thrust bearings and comparing the performance of LST bearings with that of the theoretical predictions and with the performance of standard non-texturedbearings2. BackgroundA cross section of the basic model that was analyzed in Ref. 12 is shown in figure 1. A s
12、lider having a width B is partially textured over a portion Bp =B of its width. The textured surface consists of multiple dimples with a diameter，depthand area density Sp. As a result of the hydrodynamic pressure generated by the dimples the sliding surfaces will be separated by a clearancedepending
13、 on the sliding velocity U, the uid viscosity l and the external loadIt was found in Ref. 12 that an optimum ratio exists for the parameter that provides maximum dimensionless load-carrying capacity where L isthe bearing length, and this optimum value is hp=1.25. It was further found in Ref. 12 that
14、 an optimum value exists for the textured portion a depending onthe bearing aspect ratio L/B. This behavior is shown in gure 2 for a bearing with L/B = 0.75 at various values of the area density Sp. As can be seen in the range of Sp values from 0.18 to 0.72 the optimum a value varies from 0.7 to 0.5
15、5, respectively. It can also be seen from gure 2 that for a 0.85 no optimum value exists for Sp and the maximum load W increases with increasing Sp. Hence, the largest area density that can be practically obtained with the laser texturing is desired. It is also interesting to note from gure 2 the ad
16、vantage of partial-LST (a 1) over the full LST (a = 1) for bearing applications. At Sp= 0.5, for example, the load W at a = 0.6 is about three times higher than its value at a = 1. A full account of this behavior is given in Ref. 12.3. ExperimentalThe tested bearings consist of sintered SiC disks 10
17、 mm thick, having 85 mm outer diameter and 40 mm inner diameter. Each bearing (see gure 3) comprises a at rotor (a) and a six-pad stator (b). The bearings were provided with an original surface nishby lapping to a roughness average Ra= 0.03 lm. Each pad has an aspect ratio of 0.75 when its width is
18、measured along the mean diameter of the stator. The photographs of two partial-LST stators are shown in gure 4 where the textured areas appear as brighter matt surfaces. The rst stator indicated (a) is a unidirectional bearing with the partial-LST adjacent to the leading edge of each pad, similar to
19、 the model shown in gure 1. The second stator (b) is a bi-directional version of a partial-LST bearing having two equal textured portions, a/2, on each of the pad ends. The laser texturing parameters were the following; dimple depth, dimple diameter and dimple area density Sp= 0.60.03. These dimple
20、dimensions were obtained with 4 pulses of 30 ns duration and 4 mJ each using a 5 kHz pulsating Nd:YAG laser. The textured portion of the unidirectional bearing was a= 0.73 and that of the bi-directional bearing was a= 0.63. As can be seen from gure 2 both these a values should produce load-carrying
21、capacity vary close to the maximum theoretical value.The test rig is shown schematically in gure 5. Anelectrical motor turns a spindle to which an upper holder of the rotor is attached. A second lower holder of the stator is xed to a housing, which rests on a journal bearing and an axial loading mec
22、hanism that can freely move in the axial direction. An arm that presses against a load cell and thereby permits friction torque measurements prevents the free rotation of this housing. Axial loading is provided by means of dead weights on a lever and is measured with a second load cell. A proximity
23、probe that is attached to the lower holder of the stator allows on-line measurements of the clearance change between rotor and stator as the hydrodynamic eects cause axial movement of the housing to which the stator holder is xed. Tap water is supplied by gravity from a large tank to the center of t
24、he bearing and the leakage from the bearing is collected and re-circulated. A thermocouple adjacent tothe outer diameter of the bearing allows monitoring of the water temperature as the water exit the bearing. A PC is used to collect and process data on-line. Hence,the instantaneous clearance, frict
25、ion coecient, bearing speed and exit water temperature can be monitored constantly. The test protocol includes identifying a reference “zero” point for the clearance measurements by rst loading and then unloading a stationary bearing over the full load range. Then the lowest axial load is applied, t
26、he water supply valve is opened and the motor turned on. Axial loading is increased by steps of 40 N and each load step is maintained for 5 min following the stabilization of the friction coecient ata steady-state value. The bearing speed and water temperature are monitored throughout the test for a
27、ny irregularities. The test ends when a maximum axial load of 460 N is reached or if the friction coecient exceeds a value of 0.35. At the end of the last load step the motor and water supply are turned o and the reference for the clearance measurements is rechecked. Tests are performed at two speed
28、s of 1500and 3000 rpm corresponding to average sliding velocities of 4.9 and 9.8 m/s, respectively and each test is repeated at least three times.4. Results and discussionAs a rst step the validity of the theoretical model in Ref. 12 was examined by comparing the theoretical and experimental results
29、 of bearing clearance versus bearing load for a unidirectional partial-LST bearing. The results are shown in gure 6 for the two speeds of 1500 and 3000 rpm where the solid and dashed lines correspond to the model and experiment, respectively. As can be seen, the agreement between the model and the e
30、xperiment is good, with dierences of less than 10%, as long as the load is above 150 N. At lower loads the measured experimental clearances are much larger than the model predictions, particularly at the higher speed of 3000 rpm where at 120 N the measured clearance is 20 lm, which is about 60% high
31、er than the predicted value. It turns out that the combination of such large clearances and relatively low viscosity of the water may result in turbulent uid lm. Hence, the assumption of laminar ow on which the solution of the Reynolds equation in Ref. 12 is based may be violated making the model in
32、valid especially at the higher speed and lowest load. In order to be consistent with the model of Ref. 12 it was decided to limit further comparisons to loads above 150 N.It should be noted here that the rst attempts to test the baseline untextured bearing with the original surface nish of Ra= 0.03 lm on both the stator and rotor failed due to extremely high friction even at the lower loads. On the other hand the partial-LST bearing ran smoothly throughout the load range. It was found that the post-LST lappi
