摘要:

A systematic analysis is carried out to study the effect of 3-D surface roughness on the film thickness and film breakdown in micro-elastohydrodynamic lubrication (EHL). First, the analysis focuses on the global behavior of EHL film thickness. For simplicity and without loss of generality, a 3-D sinusoidal rough surface in contact with a smooth surface is analyzed, assuming isothermal conditions. Heavily loaded contacts are examined using Hertzian peak pressures up to 2.5 GPa. Two wavelengths are separately used to generate the roughness pattern along the direction of surface motion (i.e. the longitudinal wavelength). Each simulates the surface topography with long or short wavelength. The roughness pattern perpendicular to the direction of surface motion is described by the transverse wavelength which is set independently. The average value of EHL film thickness in the Hertzian region is calculated for various transverse wavelengths of surface roughness and for four values of slide-to-roll ratio. The analysis predicts a rapid reduction of the film for small values of the transverse wavelength, suggesting a possible global breakdown of the EHL film. This possible breakdown is shown to be mainly caused by the local side flow of the lubricant around asperities in a narrow region of the Hertzian inlet and is worse under higher sliding conditions. Next, the local behavior of EHL film is analyzed. Multi-sinusoidal wave functions with various wavelengtlis and amplitudes are used to simulate contacts formed between two surfaces with random roughness. Thermal effects are also included in the analysis. Results obtained with a slide-to-roll ratio of 0.5 show an event of local film breakdown, leading to asperity collisions inside the Hertzian contact region. This film breakdown is caused by the formation and subsequent growth of a locally cavitated region as the two rough surfaces slide against each other. More extensive studies are needed to gain a further understanding of the complex time-dependent events leading to local EHL film breakdown.Presented at the 48th Annual Meeting in Calgary, Alberta, Canada May 17–20, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983315

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The mechanism of so-called arrow headed pit formation on contact surfaces under lubricated rolling-sliding cyclic contact loading was analyzed by fracture mechanics. The stress intensity factors of Modes I, II and III for an arrow-headed crack were calculated by three-dimensional numerical analysis.

ISSN:1040-2004    

DOI:10.1080/10402009408983316

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This paper presents the results of the second part of the investigation on structural stiffness and Coulomb damping in compliant foil journal bearings. In the first part, a theoretical model was developed to calculate equivalent viscous damping coefficients and structural stiffness of a bump foil strip in a journal bearing or damper. A computer program was also developed to compute the eccentricity and attitude angle of the journal static equilibrium position as well as the deflections, displacements, reacting forces, and equivalent friction coefficient of each bump on the strip. This model and program enabled further parametric studies to be conducted in the second part of the investigation, the results of which are the subject of this paper.

ISSN:1040-2004    

DOI:10.1080/10402009408983317

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Hydrostatic journal bearings are ideal elements to replace roller bearings as rotor support elements in cryogenic lurbomachinery. These bearings will be used for primary space-power applications due to their long lifetime, low friction and wear, large load capacity, and direct stiffness and damping force coefficients. The performance characteristics of turbulent flow, orifice compensated, spherical hydrostatic journal bearings are presented. These bearings allow tolerance for shaft misalignment without force degradation and are able to support axial loads, thus providing a design configuration which could be used efficiently on high-performance turbomachinery.

ISSN:1040-2004    

DOI:10.1080/10402009408983318

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The interatomic array and bond structure in crystalline states of the monochalcogenides tin selenide and gallium selenide are described and correlated with their solid lubricating capacity. Friction tests assessing their solid lubricating performance were carried out on a pin-on-disk machine. Specifically, large crystalline pieces of each inorganic solid were cut and cleaved into flat squares and subsequently rubbed against sapphire balls. In another case, fine powders of gallium selenide and tin selenide luere manually fed into the sliding interfaces of 440C pins and 440C disks. For the specific test conditions explored, friction coefficients of the sapphire/ gallium selenide and sapphire/tin selenide pairs were approximately 0.23 and approximately 0.35, respectively. The friction coefficients of 440C pin/440C disk test pairs with gallium selenide and tin selenide powders were approximately 0.22 and approximately 0.38, respectively. For comparison, a number of parallel friction tests were also performed with MoS2powders and compacts, and the results of these tests are reported. The friction data, together with the crystal-chemical knowledge and electron microscopy evidence, supported the conclusion that the solid lubricating capabilities and lubrication mechanisms of these solids are closely related to their crystal chemistry and the nature of their interlayer bonding.Presented as a Society of Trlbologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in New Orleans, Louisiana, October 24–27, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983319

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Carbon nitride (CNX) thin films were prepared by DC magnetron sputtering of a graphite target in a nitrogen ambient onto Si(100) and M2 steel substrates held at ambient temperatures. All CNxcoatings grown to a thickness of 1.5 μm are adherent and smooth. Nanoindentation studies showed that amorphous CNxthin films have hardness and effective Young's modulus comparable to those of amorphous hard carbon. In dry sliding against 52100 steel, CNx-coated M2 substrates give initial friction coefficients ˜0.1, rising to around 0.5 in the steady state. The wear life of coated M2 steels varies inversely with normal load, rising to about two orders of magnitude higher than that of uncoated M2 at a normal load of 1.3N and a sliding speed of 0.12 m/s. This improvement is attributed to the high yield strength of carbon nitride coatings.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:10.1080/10402009408983320

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An analytical model for strip rolling operating in the mixed regime is developed. The model combines analysis for the influence of bulk plastic deformation on the effective hardness of the strip asperities with an approach to allow for the influence of roughness on lubricant flow. An approximate correction for thermal effects is also included. The predictions of the model are compared with experimental measurements of film thickness and slip.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:10.1080/10402009408983321

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The friction and wear under dry sliding conditions of injection molded blends of Polyetheretherketone (PEEK) and Polyetherimide (PEI) at temperatures from 20°C to 232°C were investigated on a pin-on-disk apparatus. The friction and wear results were correlated to results obtained from dynamic mechanical thermal analysis (DMTA) temperature scans performed on each of the materials. It was found that tan δ peaks corresponding to α transitions occurring in the vicinity of the glass transition temperature (Tg) coincided with catastrophic tribological failure in the case of PEI and the amorphous PEEK/PEI blends. PEEK and the annealed 70% PEEK/30% PEI blend, exhibited marked increases in friction and wear at and above the Tg. The absence of catastrophic tribological failure in PEEK and the annealed 70/30 blend in the vicinity of the glass transition temperature corresponded to a transitions of significantly lesser strength (i.e. lower tan δ peak values) than those observed in PEI and the amorphous blends. Between 90°C and 105°Cfor PEI and 45°C and 70°C for the PEEK/PEI 50/50 blend, severe to mild friction and wear transitions were observed. DMTA results showing secondary tan δ peaks centered at 75°C for PEI and 38°C for the PEEK/PEI 50/50 blend made evident the occurrence of β transitions in these materials. It appeared that a substantial change in ductility associated with these β transitions resulted in the observed transitional tribological behavior.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:10.1080/10402009408983322

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

High-density, sputtered molybdenum disulfide films (MoS2) were investigated as lubricants for the next generation of spacecraft gimbal bearings where low torque signatures and long life are required. Low friction in a vacuum environment, virtually no out-gassing, insensitivity to low temperature, and radiation resistance of these lubricant films are valued in such applications. One hundred and twenty five thousand hours of accumulated bearing lest time were obtained on 24 pairs of flight-quality bearings ion-sputtered with three types of advanced MoS2films. Life tests were conducted in a vacuum over a simulated duty cycle for a space pay bad gimbal. Optimum retainer and ball material composition were investigated. Comparisons were made with test bearings lubricated with liquid space lubricants.

ISSN:1040-2004    

DOI:10.1080/10402009408983323

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The lubrication characteristic of dry powder is studied using the continuum theory of grain flows (1). Appropriate governing equations and boundary conditions are derived for the powder flow through the clearance space of a bearing. The equations take into account the energy loss due to grain fluctuations, and consideration is given to the particle slippage at the boundaries. As a special case, closed-form analytical solutions are derived for the average random speed, flow velocity, pressure and shear stress for the flow of grains in the clearance space of an infinitely long slider bearing. Results are presented for various performance parameters such as the load-carrying capacity and the friction coefficient.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:10.1080/10402009408983324

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor