scholarly journals An Experimental Study on Starved Grease Lubricated Contacts

Lubricants ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 82 ◽  
Author(s):  
David Gonçalves ◽  
Armando Campos ◽  
Jorge Seabra
Keyword(s):  
Experimental Study ◽  
Film Thickness ◽  
Coefficient Of Friction ◽  
Contact Area ◽  
Operating Conditions ◽  
Thickness Profile ◽  
Lubricated Contacts ◽  
The Coefficient Of Friction ◽  
Over Time ◽  
Ball On Disc

The film thickness of a ball-on-disc contact lubricated with four greases of different formulations was measured under different operating conditions until starvation. Two polymer-thickened greases and two lithium-thickened greases, formulated with base oils of different nature and/or viscosity, were tested. The central film thickness was measured under constant operating conditions (load, temperature, slide-to-roll ratio) varying only the entrainment speed. In a separate test, the film thickness was measured over time with all operating conditions set to constant. Pictures of the film thickness profile across the contact area were also registered. The results were compared with the fully flooded results. The coefficient of friction (COF) was measured in a ball-on-disc contact under equal operating conditions and the results were correlated with the film thickness findings. The different grease formulations and the influence of the operating conditions on the film thickness and COF were discussed. The polymer thickened the greases, promoting lower COF and higher film thickness, especially when there is thickener material crossing the contact which happens quite often for these greases.

Experimental Investigation of Porous Bronze Bearings

1973 ◽  
Vol 95 (2) ◽  
pp. 173-179 ◽  
Author(s):  
C. Cusano ◽  
R. M. Phelan
Keyword(s):  
Experimental Study ◽  
Experimental Investigation ◽  
Coefficient Of Friction ◽  
Boundary Lubrication ◽  
Operating Conditions ◽  
The Coefficient Of Friction ◽  
Theoretical Analyses ◽  
Lubrication Conditions

An experimental study was made of the performance of porous bronze bearings under different operating conditions. A PV value of 50,000 psi ft/min was found to be too high for the assembly used when the bearings were lubricated only by the oil initially provided within their structure. Tests at a PV value of 33,000 psi ft/min gave satisfactory results. The coefficient of friction was found to vary with load and to be almost independent of speed for the bearings tested under boundary lubrication conditions. Except for relatively light loads and moderate and higher speeds, the bearings operate under boundary lubrication conditions. When pressurized oil was supplied to the bearings, it was found that, for the same operating conditions, porous bearings run at higher eccentricity ratios than solid bearings, as predicted by theoretical analyses.

Skin-skin contact: The normal-force dependence of the coefficient of friction between a bare finger and artificial skin changes randomly

2021 ◽  
Author(s):  
Koki Inoue ◽  
Shogo Okamoto ◽  
Yasuhiro Akiyama ◽  
Yoji Yamada
Keyword(s):  
Experimental Study ◽  
Coefficient Of Friction ◽  
Normal Force ◽  
Skin Surface ◽  
Artificial Skin ◽  
Skin Changes ◽  
Root Cause ◽  
Skin Contact ◽  
The Coefficient Of Friction ◽  
Frictional Forces

Abstract This study investigates the dependence of the coefficients of friction on the normal force produced by sliding a bare finger over different artificial skins with seven levels of hardness. The coefficient of friction was modeled as a power function of the normal force. An experimental study that involved sliding a finger over artificial skin surfaces was carried out under two conditions: the fingertip being wiped by a dry cloth or a cloth soaked in ethanol. Although the exponential term was assumed to be nearly constant for identical tribological conditions, we observed that the exponent varied randomly and could be negative, zero, or positive. This probabilistic behavior has not been explicitly analyzed in previous studies on human fingertips. The probability density function of the exponent depended on the moisture content of the finger. The exponent was either nearly zero or positive when the finger sliding on the skin surface was wiped with an alcohol-soaked cloth and dried. These findings play an important role in analyzing the frictional forces produced during skin–skin contact in terms of determining the root cause behind the random variations in the dependence of the coefficient of friction on the normal force.

Stresses Due to Tangential and Normal Loads on an Elastic Solid With Application to Some Contact Stress Problems

1953 ◽  
Vol 20 (2) ◽  
pp. 157-166
Author(s):  
J. O. Smith ◽  
Chang Keng Liu
Keyword(s):  
Plane Strain ◽  
Coefficient Of Friction ◽  
Contact Area ◽  
Normal Load ◽  
Elastic Solid ◽  
Real Variable ◽  
The Body ◽  
Shearing Stress ◽  
Tangential Load ◽  
The Coefficient Of Friction

Abstract The results of two-dimensional approach using real variable method to Hertz’s problem of contact of elastic bodies are presented. Both normal and tangential loads are assumed to be distributed in Hertzian fashion over the area of contact. The magnitude of the intensity of the tangential load is assumed to be linearly proportional to that of the normal load when sliding motion of the body is impending. The stresses in the elastic body due to the application of these loads on its boundary are presented in closed form for both plane-stress and plane-strain cases. A numerical value of f = 1/3 is assumed for the linear proportionality (coefficient of friction) between the tangential and normal loads in order that the distribution of stresses may be illustrated. The significance of the stress distribution, across the contact area and in the body, is also discussed. It is shown that when the combination of loads considered in the paper are applied at the contact area of bodies in contact the maximum shearing stress may be at the surface instead of beneath the surface. For example, for plane strain, if the coefficient of friction is f = 1/3, the maximum shearing stress is at the surface and is 43 per cent larger than the maximum shearing stress, which would be below the surface, that occurs when the normal force acts alone. The effect of range of normal stress and of shearing stress on the plane of maximum shear and on the plane of maximum octahedral shear on failure by progressive fracture (fatigue) is discussed.

scholarly journals Providing the stability of the coefficient of friction of a vehicle disk brake under extreme operating conditions

2016 ◽  
Vol 37 (3) ◽  
pp. 230-236 ◽  
Author(s):  
Yu. Yu. Osenin ◽  
Douma Mansur Al-Makhdi ◽  
Yu. I. Osenin ◽  
O. V. Sergienko ◽  
I. I. Sosnov ◽  
...  
Keyword(s):  
Coefficient Of Friction ◽  
Operating Conditions ◽  
Disk Brake ◽  
The Coefficient Of Friction ◽  
The Stability

A Mixed-Lubrication Study of Journal Bearing Conformal Contacts

1997 ◽  
Vol 119 (3) ◽  
pp. 456-461 ◽  
Author(s):  
Qian (Jane) Wang ◽  
Fanghui Shi ◽  
Si C. Lee
Keyword(s):  
Film Thickness ◽  
Contact Pressure ◽  
Contact Area ◽  
Numerical Solutions ◽  
Mixed Lubrication ◽  
Lubricant Film ◽  
Operating Conditions ◽  
Asperity Contact ◽  
Lubricant Film Thickness ◽  
Asperity Contacts

Numerical analyses of finite journal bearings operating with large eccentricity ratios were conducted to better understand the mixed lubrication phenomena in conformal contacts. The average Reynolds equation derived by Patir and Cheng was utilized in the lubrication analysis. The influence function, calculated numerically using the finite element method, was employed to compute the bearing deformation. The effects of bearing surface roughness were incorporated in the present analysis for the calculations of the asperity contact pressure and the asperity contact area. The numerical solutions of the hydrodynamic and asperity contact pressures, lubricant film thickness, and asperity contact area were evaluated based on a simulated bearing-journal geometry. The calculations revealed that the asperity contact pressure may vary significantly along both the width and the circumferential directions. It was also shown that the asperity contacts and the lubricant film thickness were strongly dependent on the bearing width, asperity orientation, and operating conditions.

Predicting the Coefficient of Friction in Sliding-Rolling Contacts

1989 ◽  
Vol 111 (2) ◽  
pp. 386-390 ◽  
Author(s):  
Yufeng Li ◽  
Ali Seireg
Keyword(s):  
Surface Roughness ◽  
Coefficient Of Friction ◽  
Thermal Regime ◽  
Surface Coating ◽  
Experimental Tests ◽  
Operating Conditions ◽  
Published Data ◽  
Excellent Correlation ◽  
Rolling Contacts ◽  
The Coefficient Of Friction

This paper deals with the development of a dimensionless empirical formula for calculating the coefficient of friction in sliding-rolling steel on steel contacts under different operating conditions in the thermal regime. The effect of lubrication, surface roughness, and surface coating on friction are considered. The formula shows excellent correlation with the experimental tests conducted by many investigators and provides a unified relationship for all the published data.

A Study of Roughness and Non-Newtonian Effects in Lubricated Contacts

2005 ◽  
Vol 127 (3) ◽  
pp. 575-581 ◽  
Author(s):  
Malal Kane ◽  
Benyebka Bou-Said
Keyword(s):  
Film Thickness ◽  
Numerical Solutions ◽  
Operating Conditions ◽  
Homogenization Theory ◽  
Roughness Effects ◽  
Small Surface ◽  
Lubricated Contacts ◽  
Lubricated Contact ◽  
A New Technique ◽  
Numer Anal

This article is concerned with the simulation of a lubricated contact considering the fluid to be non-Newtonian of the Maxwell type. Severe operating conditions lead to very small surface-to-surface distances. In this situation it is necessary to take roughness effects into account. A popular method consists in averaging the film thickness following Patir and Cheng (ASME J. Lubr. Technol., 100, pp. 12–17, 1978), or more recently Wang et al. (Tribol. Trans., 45(1), pp. 1–10, 2000), with good reported results compared with experimental data. To overcome certain limitations that become apparent at very small film thickness, notably when the roughness is two-dimensional, in 1995 Jai (Math. Modell. Numer. Anal., 29(2), pp. 199–233, 1995) introduced a new technique based on a rigorous homogenization theory in the case of compressible fluid flow. This procedure was further mathematically developed by Buscaglia and Jai (Math. Probl. Eng., 7(4), pp. 355–377, 2001) and applied to tribological problems by Jai and Bou-Saı¨d (ASME J. Tribol., 124, pp. 327–355, 2002). In this paper, we propose a similar homogenized approach in the case of non-Newtonian fluids to avoid numerical problems which are often encountered in other approaches. Results in the homogenized roughness case are obtained and compared with direct numerical solutions.

Determination of Tire-Road Friction Coefficients for Skid Mark Analysis

1985 ◽  
Vol 13 (1) ◽  
pp. 41-64
Author(s):  
W. R. Garrott ◽  
D. A. Guenther
Keyword(s):  
Experimental Study ◽  
Coefficient Of Friction ◽  
Friction Coefficients ◽  
Pickup Truck ◽  
The Road ◽  
Heavy Trucks ◽  
Road Friction ◽  
Brake Application ◽  
The Coefficient Of Friction

Abstract An experimental study was made to compare the validities of methods currently used by accident reconstructionists to determine the coefficient of friction between the road and the vehicle tires at the time of an incident. This value could then be used in conjunction with skid mark length and vehicle weight to calculate the prebraking speed of the vehicle. Three automobiles and three trucks with a variety of tires and loadings were used on a variety of pavements. The accuracy and area of applicability of each of four methods for obtaining friction coefficients were determined by relating the prebraking speed calculated from each to the actual speed at the time of brake application. All four methods were satisfactory for automobiles and the pickup truck used, but only two were acceptable for heavy trucks. The most valid coefficients are obtained from skid mark lengths obtained under conditions duplicating those in an incident.

Metrological Assessment of the Coefficient of Friction of Various Types of Silica Using the Motor Current During ILD-CMP

2004 ◽  
Vol 816 ◽  
Author(s):  
Harald Jacobsen ◽  
Eric Stachowiak ◽  
Gerfried Zwicker ◽  
Wolfgang Lortz ◽  
Ralph Brandes
Keyword(s):  
Shear Rate ◽  
Film Thickness ◽  
Coefficient Of Friction ◽  
Removal Rate ◽  
Rate Range ◽  
Systematic Assessment ◽  
Parameter Domain ◽  
Motor Current ◽  
First Approximation ◽  
The Coefficient Of Friction

AbstractIn the work presented the coefficient of friction (COF) was firstly determined metrologically by a systematic assessment of motor currents for different products of pressure and velocity (p v). With all seven test slurries it could be shown that the inserted energy ECMP is proportional to the product of pressure and velocity. The COF of the parameter domain considered here does not depend on the inserted energy or the product of p v in a first approximation. For all tested slurries it was demonstrated that, both the COF and the removal rate (RR) behave analogously (low COF→ low RR).Measurements of the viscosity η have shown that η is not a constant in the shear rate range relevant for CMP. Using the obtained viscosity values a mean slurry film thickness in the range of 2,5 -C 6 μm could be calculated.

Modelling the tribological response in dry sliding of boron modified as-cast Ti6Al4V on hardened steel

2021 ◽  
pp. 135065012110592
Author(s):  
Palash Roy Choudhury ◽  
Korimilli Eswar Prasad ◽  
John K. Schueller ◽  
Abhijit Bhattacharyya
Keyword(s):  
Wear Rate ◽  
Coefficient Of Friction ◽  
Boron Content ◽  
Normal Load ◽  
Operating Conditions ◽  
Dry Sliding ◽  
Contour Plots ◽  
The Coefficient Of Friction ◽  
En 31 ◽  
Full Factorial

Tribological characteristics of boron modified as-cast Ti6Al4V alloys are not very well known, but these alloys enjoy improved as-cast mechanical properties and favourable manufacturing economy. Experimental results are reported here for the effects of sliding speed and normal load on the wear rate and the coefficient of friction in dry sliding of these alloys on hardened EN 31 steel. Alloys having 0%, 0.30%, and 0.55% boron by weight were tested. A full factorial experiment assessed the effects of boron content, speed, and load on wear and friction. Interactions between speed and load were found to be statistically significant in influencing the wear rate and the coefficient of friction. Regression models are developed to predict the wear rate and coefficient of friction responses. The developed contour plots can assist designers in choosing operating conditions when selecting these alloys even if the wear mechanisms are unknown. Evidence shows that the wear resistance of Ti6Al4V can be improved by boron addition, and wear regimes are sensitive to boron content.

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