On the Effect of Hydrodynamic Action on the Contact Area of Highly Loaded Line Contacts

1984 ◽  
Vol 106 (1) ◽  
pp. 152-155
Author(s):  
M. O. A. Mokhtar ◽  
A. A. Abdel-Ghany
Keyword(s):  
Contact Area ◽  
Local Deformation ◽  
Hertzian Contact ◽  
Oil Film ◽  
Operating Variables ◽  
Lubricant Oil ◽  
Line Contacts ◽  
Hydrodynamic Solution ◽  
Heavy Loads ◽  
Highly Loaded

The elastically deformed contact area together with the oil film thickness between lubricated plane cylinders in relative motion are experimentally measured and analyzed under various loads and speeds. The measured contact profile has shown to be a function of the operating variables and consequently represents a justifying means in deciding the appropriate solutions to the lubrication problem in concentrated contacts. Under heavy loads and very low speeds, the deformation at the contact zone approaches the flat Hertzian contact, while at increased speeds elastohydrodynamic regimes prevail and relatively thick oil film could form with the presence of a local constriction at the trailing oil exit end. By further speeding up the local deformation diminishes and full (rigid) hydrodynamic solution would govern the lubricant oil behavior with minimum local deformations.

Nano-Meter Film Rheology and Asperity Lubrication

2002 ◽  
Vol 124 (3) ◽  
pp. 595-599 ◽  
Author(s):  
Bo Jacobson
Keyword(s):  
Contact Area ◽  
Pressure Fluctuations ◽  
Slip Rate ◽  
Hertzian Contact ◽  
Metal Contact ◽  
Rolling Motion ◽  
Oil Film ◽  
Pure Rolling ◽  
Total Separation ◽  
Molecular Dimensions

It is today possible to manufacture so smooth surfaces that they can elastically conform totally to each other over the whole Hertzian contact area. For pure rolling lubrication such surfaces only need an oil film of molecular dimensions to get total separation. When the rolling motion is combined with sliding, the pressure fluctuations inside the Hertzian contact redistribute the oil and make metal-to-metal contact possible. The redistribution velocity is a function of the slip rate S and the number of asperities N from the inlet to the outlet of the Hertzian contact area. The asperity top oil film thickness decreases with a factor of the order 2NS going from the inlet to the outlet of the Hertzian contact.

A Study of the Effect of m and n Coefficients of the Hertzian Contact Theory on Railroad Vehicle Dynamics

2007 ◽  
Author(s):  
J. P. Pascal ◽  
Khaled E. Zaazaa
Keyword(s):  
Contact Area ◽  
Contact Region ◽  
Local Deformation ◽  
Hertzian Contact ◽  
Vehicle Dynamic ◽  
Railroad Vehicle Dynamics ◽  
Original Table ◽  
Data Points ◽  
Railroad Vehicle ◽  
Contact Ellipse

For the wheel/rail contact problem, the Hertz theory for two elastic bodies in contact is commonly used to determine the shape and dimensions of the contact area and the local deformation of the wheel and rail surfaces at the contact region. The shape of the contact area is assumed to be elliptical. The ratio of the contact ellipse semi-axes is equal to the ratio of two non-dimensional contact area coefficients, known as m and n coefficients. Hertz presented a table of these two coefficients, determined as a function of an angular parameter, θ. Most railroad vehicle dynamic codes use this table with online interpolation to determine the contact ellipse semi-axes. Recently, it was found that this original table may be too coarse, and that more data points are needed within the table for solving the wheel/rail contact accurately. This paper discusses the effect of the accuracy of the m and n coefficients in solving for wheel/rail contact, and demonstrates this effect with two numerical examples that show the resulting differences in the dynamic behavior of railroad vehicles dependent on this accuracy. A new table with more data points is presented that is recommended for use in railroad vehicle dynamic codes that employ the Hertzian contact for solving the wheel/rail contact interaction. This modified table was originally derived by Jean-Pierre Pascal as a part of collaborative research between the Federal Railroad Administration (FRA) and the French Ministry of Transportation.

scholarly journals Improved design criterion for frictionally engaged contacts in overrunning clutches

2021 ◽  
Author(s):  
Nadine Nagler ◽  
Armin Lohrengel
Keyword(s):  
Design Process ◽  
Contact Area ◽  
Axial Load ◽  
State Of The Art ◽  
Tangential Force ◽  
Design Criterion ◽  
Hertzian Contact ◽  
Loss Of Function ◽  
Axial Loads ◽  
Improved Design

AbstractOverrunning clutches, also known as freewheel clutches, are frictionally engaged, directional clutches; they transmit torque depending on the Freewheel clutch rings’ rotation directions. The torque causes a tangential force in the Hertzian contact area. The hitherto “state-of-the-art design criterion” bases on this load situation. In practice, axial loads additionally act on the frictionally engaged Hertzian contact area. This additional axial load can cause the loss of the friction connection and so the freewheel clutch slips. This publication presents an improved design criterion for frictionally engaged contacts in freewheel clutches. It allows to consider tangential as well as axial loads during the design process. Additionally, it offers the possibility to estimate the probability of frictional engagement loss and gross slip based on the freewheel clutch’s application scenario. This publication points out how to use the improved design criterion to design freewheel clutches that are more robust against a loss of function.

Experimental and numerical study on cavitation under elastohydrodynamic lubrication point contact

2021 ◽  
pp. 135065012110527
Author(s):  
Mingfei Ma ◽  
Wen Wang ◽  
Wenxun Jiang
Keyword(s):  
Contact Area ◽  
Numerical Study ◽  
Ambient Pressure ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Hertzian Contact ◽  
Pressure Area ◽  
Cavitation Pressure ◽  
Experimental Researches ◽  
State 1

As a common phenomenon in elastohydrodynamic lubrication, cavitation has an effect on the completeness of the oil film in the contact area. Many studies have therefore been conducted on cavitation. Experimental researches on cavitation usually rely on optical interference observation, which offers a limited resolution and observation range. In this paper, an infrared thermal camera is used to observe the cavity bubbles on a ball-on-disc setup under sliding/rolling conditions. The results show that the cavity length increases with an increases of the entrainment speed and the viscosity of the lubricants. These observations are explained by a numerical model based on Elrod's algorithm. Effects of entrainment speed and lubricant viscosity on the breakup of cavitation bubbles and the cavitation states are investigated. Both the simulation and experimental results show that a negative pressure area is present behind the Hertzian contact area. The ambient pressure plays a role in maintaining cavitation state 1. The cavitation pressure is close to the vacuum pressure when the entrainment speed is low and to the ambient pressure instead when the entrainment speed is high.

Lubrication Characteristics of Electric Sliding Contacts Consisting of Rotating Circular Grooved Disk and Stationary Rider With Spherical Surface Under Lubricated Condition

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Satoru Kaneko ◽  
Hiroo Taura ◽  
Ryosuke Fukasawa ◽  
Hitoshi Kanai
Keyword(s):  
Frictional Force ◽  
Spherical Surface ◽  
Disk Surface ◽  
Cross Sectional Area ◽  
Metal Contact ◽  
Sectional Area ◽  
Sliding Contacts ◽  
Cross Sectional ◽  
Oil Film ◽  
Lubricant Oil

Electric sliding contacts are widely used in various electrical components such as for home appliances and automobiles. The purpose of the present study is to improve the performance characteristics of the electric sliding contacts operating under the lubricated condition by the combination of circular grooved disk and rider with a spherical surface. The experimental and theoretical analyses have been carried out to investigate the effect of cross-sectional area of circular grooves provided in the rotating disk surface on the frictional characteristics and the electrical conductivity. The experimental analysis is conducted with a pin-on-disk friction tester to measure the frictional force and the contact voltage between the sliding contacts under the lubricated condition. The oil-film force and the frictional force between the rider and disk are also calculated with the Reynolds equation and they are found to be closely corresponding to the experimental results. The results obtained in the present study show that increasing the cross-sectional area of the circular grooves on the disk extends the operation condition yielding the metal contact to a higher value of the bearing characteristic number S, which is defined by ηU0L0λ/W (η is the lubricant oil viscosity, U0 is the sliding velocity, L0 is the rider arc length in the sliding direction at the middle of radial width, W is the applied load, and λ is the aspect ratio of rider), and also decreases the frictional force at the maximum value of S at which the rider could contact with the disk surface. These are expected since upstream lubricant oil dragged into the contact region tends to easily leak out along the circular grooves, yielding a lower oil-film force between the rider and disk and enhancing the metal contact.

scholarly journals The Elastic Contact of Rough Spheres Investigated Using a Deterministic Multi-Asperity Model

2019 ◽  
Vol 10 (01) ◽  
pp. 1841002 ◽  
Author(s):  
Vladislav A. Yastrebov
Keyword(s):  
Contact Area ◽  
Rough Surfaces ◽  
Contact Problems ◽  
Hertzian Contact ◽  
Contact Radius ◽  
Geometrical Shape ◽  
Elastic Contact ◽  
Deterministic Analysis ◽  
Asperity Model ◽  
Deformation Modes

In this paper, we use a deterministic multi-asperity model to investigate the elastic contact of rough spheres. Synthetic rough surfaces with controllable spectra were used to identify individual asperities, their locations and curvatures. The deterministic analysis enables to capture both particular deformation modes of individual rough surfaces and also statistical deformation regimes, which involve averaging over a big number of roughness realizations. Two regimes of contact area growth were identified: the Hertzian regime at light loads at the scale of a single asperity, and the linear regime at higher loads involving multiple contacting asperities. The transition between the regimes occurs at the load which depends on the second and the fourth spectral moments. It is shown that at light indentation the radius of circumference delimiting the contact area is always considerably larger than Hertzian contact radius. Therefore, it suggests that there is no scale separation in contact problems at light loads. In particular, the geometrical shape cannot be considered separately from the surface roughness at least for approaching greater than one standard roughness deviation.

Hertzian Contact and Adhesion of Elastomers

1969 ◽  
Vol 91 (4) ◽  
pp. 732-737 ◽  
Author(s):  
Richard C. Drutowski
Keyword(s):  
Stress Distribution ◽  
Tensile Stress ◽  
Contact Area ◽  
Hard Sphere ◽  
Continuous Measurement ◽  
Hertzian Contact ◽  
Initial Contact ◽  
Circular Zone ◽  
Outer Annulus ◽  
Contact Size

The contact of a hard sphere with a flat elastomer is examined both analytically and experimentally when adhesive stresses are present. Use of a transparent spherical indenter enables continuous measurement of contact size while the samples are pulled apart. For any combination of load and contact area, the superposition of a Hertz and a Boussinesq stress distribution separates the contact into a circular zone under compression and an outer annulus under tension. During separation, while the contact size decreases and the tensile annulus becomes a larger percentage of the total contact, the average tensile stress remains constant. This average adhesive is a material property which is easily measured and is shown to be invariant with respect to indenter radius and initial contact pressure. An application of this analysis to opaque indenters is described.

Effect of Thermal Properties of a Coated Elastohydrodynamic Lubrication Line Contact Under Various Slide-to-Roll Ratios

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Huaiju Liu ◽  
Caichao Zhu ◽  
Zonglin Gu ◽  
Zhanjiang Wang ◽  
Jinyuan Tang
Keyword(s):  
Mechanical Properties ◽  
Thermal Properties ◽  
Elastohydrodynamic Lubrication ◽  
Temperature Fields ◽  
Line Contact ◽  
Oil Film ◽  
Line Contacts ◽  
Energy Equations ◽  
Thermal Conductivities

A numerical thermal elastohydrodynamic lubrication (EHL) model is developed for coated line contacts by considering both the mechanical properties and the thermal properties of the coating and the substrate. The temperature fields within the oil film and within the solids are solved by deriving the energy equations for the solids and the oil film. Heat continuity conditions are satisfied at the interfaces between the solids and the oil film, and the coating/substrate interfaces. Effects of the slide-to-roll ratio (SR), the thermal conductivities of the coating bodies, and the oil film on temperature fields are studied.

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