摘要:

Rolling/sliding contact fatigue tests were carried out on a two-disc machine. Transverse and longitudinal furrows and conical and spherical dents were made on each specimen surface to trigger surface or near surface crack initiation. The experiment results show that the size of the defect did not have a strong influence on crack initiation, but the height of the edge buildup was the dominant parameter on surface crack initiation. Variables, such as surface roughness, hardness and temperature, were investigated to determine their influence on crack initiation. In the cases presented, surface cracks were easily found for film thickness parameters less than 0.3. When film thickness was greater than 0.5, cracks on the parts of the surface which were far away from the defects were difficult to find. It was noted that for the higher hardness specimen, the crack initiation life was longer. The reason for a crack being initiated on the specimen near the leading edge of the defects was explained by the micro-EHL analysis. It was noted that surface cracks might not always propagate. The propagation rate could also be influenced by roughness, hardness and temperature.Presented at the 46th Annual Meeting in Montreal, Quebec, Canada April 29–May 2, 1991

ISSN:1040-2004    

DOI:10.1080/10402009408983260

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A counter rotating bearing rig has been designed and constructed to study transient elastohydrodynamic lubrication phenomena. This paper describes new instrumentation, and documents test procedures. Ball and race speed measurement systems and the capacitance (film thickness) measurement system were upgraded. Methods for measuring bearing torque and race temperatures were implemented.Presented at the 47th Annual Meeting in Philadelphia, Pennsylvania May 4-7, 1992

ISSN:1040-2004    

DOI:10.1080/10402009408983261

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Wear of unidirectional continuous fiber-reinforced polymer composites with fiber orientation normal to the contact plane, sliding over scribed stainless steel disks having a controlled surface topography, is investigated in relation to the tensile stresses developed near the contact region. The composite is modeled as a transversely isotropic half-space whose effective elastic moduli are estimated from composite micro-mechanical considerations. The scribed disk is treated as a rough surface whose controlled topographical features serve as model hemispherical indenters against the composite. With friction coefficients obtained from, the wear experiments, the tensile stress field at and below the composite surface is estimated. From this, an estimate of the theoretical depth of fiber-matrix separation (fiber debonding) is calculated based on the composite transverse tensile strength. A correlation between the wear rate and theoretical depth of debonding was shown for several composites.Presented at the 48th Annual Meeting in Calgary, Alberta, Canada May 17–20, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983262

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A numerical analysis to predict the static and dynamic performance characteristics of gas annular seals at off-center conditions is presented. Isothermal rotor and stator surfaces are assumed according to conditions observed on an existing test rig. Heat flow to the rotor and stator is modeled by bulk-flow heat transfer coefficients. The non-linear differential equations for the turbulent bulk flow in the annular seal are solved using an efficient CFD algorithm. A perturbation method for calculation of the zeroth- and first-order flow fields determines the seal steady-state response and dynamic force coefficients. Numerical predictions for a test seal show that heat transfer from the bounding solid surfaces to the fluid film is important to correctly predict the temperature field. An adiabatic flow assumption leads to unrealistically large temperature drops across the seal length. The seal leakage and the direct stiffness coefficients are insensitive to the position of the rotor center in the seal, while the seal forces, the cross-coupled stiffness, and the direct damping coefficients increase with the rotor static eccentricity.Presented at the 48th Annual Meeting in Calgary, Alberta, Canada May 17–20, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983263

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The effects of membrane stresses which result from both viscous drag and the three-dimensional structure of an incompressible journal foil bearing are discussed. The structural model includes combined bending, membrane, and elastic foundation effects. The pressure in the lubricant film is predicted using an incompressible Reynolds equation. Finite element methods are used to predict both the structural deflections and the pressures in the lubricant film. Results will demonstrate that membrane effects are significant in an elastically supported foil bearing where elastic foundation effects are normally considered to provide the primary resistance to deflection. The effects of viscous drag are small but not insignificant.Presented at the 48th Annual Meeting in Calgary, Alberta, Canada May 17–20, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983264

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Pure rolling contact fatigue tests were carried out on a two-disc machine. The longitudinal cracks were initiated on the specimen surface with pure rolling and rough driving disc conditions. Cracks were easily formed from the initial longitudinal finishing grooves on the surface. The crack distribution in the wear track depended on the elastohydrodynamic lubrication (EHL) condition. If the film thickness parameter A was less than 0.1, most of the cracks were found at the center part of the wear track. With increasing A, cracks were located towards the two sides of the wear track. When A was greater than 0.5, the initiation of surface cracks was difficult except in the region near the surface defects. Three mechanisms of crack initiation under pure rolling conditions are postulated based on the micro-macro contact mechanics and micro-EHL theory.Presented at the 48th Annual Meeting in Calgary, Alberta, Canada May 17–20, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983265

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A homologous series of carboxylic acid monolayers was deposited on glass and steel surfaces by the Langmuir-Blodgett technique, and the resulting films were characterized by infrared reflection-absorption spectroscopy, X-ray photoelectron spectroscopy, and contact angle measurements. The friction and durabilities of the well-ordered, close-packed monolayer films on both substrates were evaluated using a reciprocating sliding apparatus, and the results were related to carboxylic acid chain length and monolayer film density. For even-numbered, straight chain carboxylic acids with 12-26 carbon atoms, the friction was found to be independent of the acid chain length and the surface density of the monolayer, but the durabilities increased with each. Durabilities on glass were two orders of magnitude greater than those on steel.Presented at the 47th Annual Meeting in Philadelphia, Pennsylvania May 4-7, 1992

ISSN:1040-2004    

DOI:10.1080/10402009408983266

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In pin-on-disk tests using alumina-on-alumina, it was found that the monoester of C36dimer acid and ethylene glycol was effective in reducing wear. For example, the addition of 1% of this monoester to hexadecane reduced the volumetric wear of alumina by over 40%. The monoester, originally designed to function through a process of tribopolymerization, has been found in previous studies to be effective in reducing wear in steel systems under severe conditions of boundary lubrication. Using alumina test specimens from pin-on-disk experiments, studies of the wear scars and tracks were made in an effort to understand the detailed surface chemical and tribochemical reactions that might be occurring. The techniques included photomacrography, scanning electron microscopy and Fourier transform infrared microspectroscopy. The results of this study showed evidence of a surface reaction between the monoester and alumina substrate as well as tribopolymerization. Based on these findings, a possible new mechanism of antiwear action is suggested—one that involves an initial chemical reaction with the surface followed by the formation and growth of oligomer/polymer chains somewhat similar in structure to a Langmuir-Blodgett multilayer.Presented at the 48th Annual Meeting in Calgary, Alberta, Canada May 17–20, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983267

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A theoretical model is developed to explain oil consumption in IC engines, based on the mechanism of oil being blown from a puddle directly below the top ring gap through the top ring gap into the combustion chamber during top ring reversal. This phenomenon is widely reported in the literature and is hereafter deemed the puddle theory of oil consumption. The model developed is supported by experiments conducted on a small, production single-cylinder diesel engine at various speeds using two oils. The collected data were used to construct semi-empirical, non-dimensional scaling laws to predict oil consumption. The formulas presented are capable of predicting oil consumption within ten percent, the experimental accuracy.Presented at the 48th Annual Meeting in Calgary, Alberta, Canada May 17–20, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983268

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A new ball bearing behavior model which predicts and locates power losses in a high-speed gearbox angular contact ball bearing, operating under axial and radial loads, is presented. Its new features come from the consideration of both cage action and effect of lubricant film thickness in the computation of bearing kinematics at equilibrium. Lubricant rheological properties are used in order to calculate hydrodynamic and elastohydrodynamic forces in each lubricated contact of the mechanism. This model considers cage and ball kinematics to be unknowns. These are obtained by setting motion equations for each bearing element. The computation and the location of power losses are given by the friction forces and the sliding speeds among the various bearing elements, i.e., contact between ball and inner or outer ring, ball-cage, and cage-ring.

ISSN:1040-2004    

DOI:10.1080/10402009408983269

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor