摘要:

Compliant foil bearings operate on either gas or liquid, which makes them very attractive for use in extreme environments such as in high-temperature aircraft turbine engines and cryogenic turbopumps. However, a lack of analytical models to predict the dynamic characteristics of foil bearings forces the bearing designer to rely on prototype testing, which is time-consuming and expensive. In this paper, the authors present a theoretical model to predict the structural stiffness and damping coefficients of the bump foil strip in a journal bearing or damper. Stiffness is calculated based on the perturbation of the journal center with respect to its static equilibrium position. The equivalent viscous damping coefficients are determined based on the area of a closed hysteresis loop of the journal center motion. The authors found, theoretically, that the energy dissipated from this loop was mostly contributed by the frictional motion between contact surfaces. In addition, the source and mechanism of the nonlinear behavior of the bump foil strips were examined. With the introduction of this enhanced model, the analytical tools are now available for the design of compliant foil bearings.Presented at the 48th Annual Meeting in Calgary, Alberta, Canada May 17–20, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983325

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A hydrodynamic bearing test rig was used to experimentally study the steady operating characteristics and dynamic coefficient of a plain two-axial groove journal bearing. Using two electrodynamic shakers to generate synchronous sinusoidal excitations, two small independent elliptical displacement orbits were produced for different static equilibrium positions. Data was measured for two fixed shaft speeds, while the steady load was varied to achieve Sommerfeld numbers ranging from 0.063 to 0.344. The four linearized stiffness and four linearized damping coefficients were determined for each speed-load condition by reducing the orbital data using an average magnitude and phase method. The coefficients are presented in dimensionless form as functions of the Sommerfeld number. Typical average uncertainty was found to be 12 percent for the coefficients and 8 percent for the Sommelfeld number. For the speed, load, and temperature ranges tested herein, the dynamic coefficient results for each speed agreed within the uncertainty of the data, supporting the first order approximation that, for the operating range studied, a coefficient's magnitude is independent of the absolute speed, load, and viscosity so long as the Sommerfeld number is matched. The same conclusion was reached for the steady operating location within the bearing clearance space. The overall consistency of these results also lends confidence as to their reliability. Additional experimental results presented include three sets of continuous circumferential oil film thickness and pressure profiles, and discrete temperatures.Presented as a Society of Tribologists and Lubrication Engineers paper at the STLEIASME Tribology Conference in New Orleans, Louisiana, October 24–27, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983326

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An oil-in-water emulsion in the inlet zone of a concentrated contact is modeled by treating the oil particles as flattened cylinders surrounded by water. In an independent flow model, the oil and water flows are coupled only through the pressure gradient. However, the model leads to anomalous behavior with regard to the flow of water. To overcome this problem, corrections to the pressure gradients due to interactions between the oil and water were derived. Both models showed that the emulsion became concentrated because the higher viscosity oil was preferentially drawn into the conjunction. The net effect was similar to an inlet starved of oil. The inlet film thickness predicted by the interactive theory was in good agreement with Dow's experimental measurements for an EHL contact.Presented at the 48th Annual Meeting in Calgary, Alberta, Canada May 17–20, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983327

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Abrasion testing was performed on DC sputtered hydrogenated carbon films on commercial thin-film disks processed under several conditions. Four film characteristics were found to influence the abrasion resistance of the disk, i.e., roughness, film adhesion, carbon toughness, and coefficient of friction. It was found that both fine-scale surface topography from the sputtered layer and substrate texture degraded abrasion resistance. Excellent abrasion resistance was observed for carbon films as thin as 10 nm on polished substrates when the magnetic film topography was minimized. Film adhesion was degraded by exposure to temperature and humidity. Hydrogen incorporation into the carbon films reduced film hardness which degraded abrasion resistance.Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in New Orleans, Louisiana, October 24–27, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983328

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Using a slider-on-disk type wear tester, the friction and wear characteristics of aramid fiber-reinforced brake pads were studied. Experiments showed that a tenfold decrease in the wear rate and a halving of the friction coefficient were achieved by the addition of aramid fibers. To clarify the role of aramid fibers, the analysis of the worn surfaces of pads and disks and wear particles was done using SEM and their compositions were analyzed using EPMA. These analyses showed that a strong transfer film, which was formed by the addition of aramid fibers, played an important role in the wear process.Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in New Orleans, Louisiana, October 24–27, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983329

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Magnetic storage discs overcoated under different conditions with sputtered carbon in the presence of hydrogen were analyzed for hydrogen/carbon content by nuclear reaction analysis (NRH:C), for thickness and optical absorption by ellipsometry, for carbon structure (D and G bands) by fast micro-Raman spectrophotometry, and for C-H bonds by polarized reflection Fourier transform infrared (FTIR) spectrophotometry. CSS wear performances were compared with the analytical data. It was observed that wear performance improved with increases of D and G Raman band frequencies, DIG Raman intensity ratios, integrated CH2band intensity in the FTIR spectrum, and optical absorptivity, but with decreases of NRAH:C, up to a limiting value. A structural model is proposed to account for the observations.

ISSN:1040-2004    

DOI:10.1080/10402009408983330

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Electroless nickel-phosphorous alloy was plated onto quenched and hardened stainless steel. Laser surface treatments by YAG laser beams were carried out with the objective of improving -both the wear and the corrosion resistance of the platings. The friction and wear properties of the laser-treated platings were compared to unplated, untreated plated, and 400°C heat-treated plated substrates in pin-on-disc tests under unlubricated conditions. It was shown that laser treatments gave about a ten percent reduction in the friction coefficient compared with unplated substrates, and that controlled laser-treated plating improved the wear resistance of untreated plating to a level equivalent to 400°C heat-treated plating. It was found that the salt-spray corrosion resistance of the laser-treated platings was much greater than the unplated material and the 400°C heat-treated plating. The laser treatment is capable of improving both wear and corrosion resistance; and the wear resistance is externally governed by the hardness of the plating, and the corrosion resistance is governed by the crystal structure, especially the amount of amorphous nickel.Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in New Orleans, Louisiana, October 24–27, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983331

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The film-forming properties of solutions of low-to-medium molecular weight polyisoprenes in synthetic hydrocarbon have been studied using thin film interferometry. It has been shown that the lubricating films formed in rolling, concentrated contacts have two components. At very slow speeds, the polymer forms an immobile film of thickness equivalent to two radii of gyration of the polymer molecules. This film thickness is independent of speed but is gradually squeezed from the contact when motion is halted. The film is likely to represent two monolayers of polymer, one on each surface, and can be regarded as a boundary lubricating film. As the rolling speed is raised, a conventional elastohydrodynamic film is formed which is superimposed on the immobile film.

ISSN:1040-2004    

DOI:10.1080/10402009408983332

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The frictional behavior of certain nitrogen-containing ceramics, such as silicon nitride, alpha sialons, and beta sialons as journal materials were studied in conformal contact with a tin-coated Al-Si alloy (Al-Si/Sn), forged 1141 steel and a cast aluminum matrix composite with silicon carbide reinforcement (cast MMC) as bearing materials while lubricated with SAE WW30. A case-hardened 1016 steel was also tested with the Al-Si/Sn and cast MMC bearings under the same conditions. The friction values of the ceramic and the steel journal wear pairs were compared and their frictional behaviors were evaluated.

ISSN:1040-2004    

DOI:10.1080/10402009408983333

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The demand for high quality and fully automated production, coupled with advances in alloy development, focuses attention on the surface condition of products, especially the residual stresses on the machined surface because of its effect on component performance, longevity, and reliability. Although stainless steel is an important, material with wide application, it is not easy to obtain favorable surface condition, due to its sensitivity to thermal and mechanical operations. In order to obtain favorable surface conditions in a stainless steel component, it is necessary to have practical data which include information concerning tool wear, surface roughness and surface residual stress. In the research toward developing a machinability chart which can provide suitable cutting parameters for the high production rate and good quality surface, and can be used in computer controlled machining tools, surface residual stress distributions in the turning process for stainless steel were studied. Austenitic 304 stainless steel bars were selected as the workpieces and uncoated carbide tools were used in the tests. The obtained results will show residual stress conditions on the machined stainless steel components varying according to cutting conditions.Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in New Orleans, Louisiana, October 24–27, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983334

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor