Normal and Angular Motions at Rough Planar Contacts During Sliding With Friction

1992 ◽  
Vol 114 (3) ◽  
pp. 567-578 ◽  
Author(s):  
D. P. Hess ◽  
A. Soom
Keyword(s):  
Nonlinear Equations ◽  
Contact Force ◽  
Contact Area ◽  
Normal Contact ◽  
Frictional Contacts ◽  
Normal Contact Force ◽  
The Real ◽  
Real Area Of Contact ◽  
Real Area ◽  
Contact Vibrations

The planar dynamics of a rough block in nominally stationary or sliding contact with a counter-surface is studied in this work. Starting with the Greenwood-Williamson model of a rough surface, the analysis of elastic contact deflections is extended to accommodate angular as well as normal motions. The real area of contact and the normal contact force are obtained in terms of the relative approach and orientation of the surfaces. It is shown that angular and normal motions at frictional contacts are generally coupled. The contact area and normal contact force are shown to be nonlinearly related to the normal and angular motions. However, the contact area remains proportional to the normal load, even in the presence of angular motions. When the friction force is assumed to be proportional to the real area of contact, the coefficient of sliding friction will be unchanged by small relative rotations between the sliding bodies. Based on this contact and friction model, the nonlinear equations of motion that describe the planar contact vibrations of a sliding block can be written directly. Although a detailed analysis of the stability and response characteristics of these nonlinear equations is beyond the scope of the present work, a limited comparison of calculations and measurements taken on both stationary and sliding blocks indicate that the small amplitude contact vibrations are reasonably well captured by the model developed in this work.

The Effects of Relative Angular Motions on Friction at Rough Planar Contacts

1993 ◽  
Vol 115 (1) ◽  
pp. 96-101 ◽  
Author(s):  
D. P. Hess ◽  
A. Soom
Keyword(s):  
Rough Surface ◽  
Friction Force ◽  
Contact Force ◽  
Coefficient Of Friction ◽  
Angular Displacement ◽  
Normal Contact ◽  
Normal Contact Force ◽  
The Real ◽  
The Coefficient Of Friction ◽  
Real Area

Changes in friction due to angular motions at rough planar contacts are investigated using a compliant contact model that isolates an angular degree-of-freedom. Expressions are developed that relate the real area of contact, the contact forces and the line-of-action of the resultant normal contact force to the angular displacement for both periodic and random rough surfaces. We assume that the friction force is proportional to the real area of (elastic) contact. For a periodic rough surface, consisting of an array of hemispherical asperities of equal height and radius, the friction force is shown to be independent of angular displacement. The normal force increases and its line-of-action shifts away from the center of the contact as angular displacements increase. Therefore, the coefficient of friction decreases with angular displacement. In contrast, for a randomly rough surface, the contact area and normal contact force are shown to be non-linearly dependent on angular displacement, but remain proportional to each other in the presence of relative angular motion. Therefore, for the randomly rough surfaces the coefficient of friction is independent of angular motion.

scholarly journals A novel friction law

2012 ◽  
Vol 16 (5) ◽  
pp. 1529-1533 ◽  
Author(s):  
Hai-Yan Kong ◽  
Ji-Huan He
Keyword(s):  
Dimensional Analysis ◽  
Influencing Factors ◽  
Friction Force ◽  
Contact Force ◽  
Contact Area ◽  
Frictional Force ◽  
Normal Contact ◽  
Normal Contact Force ◽  
Friction Law ◽  
Miniaturized Devices

Frictional force is a vitally important factor in the application of engineering either in macroscopic contacts or in micro/nanoscale contacts. Understanding of the influencing factors about frictional force is essential for the design of miniaturized devices and the use of minimal friction force. In the paper, dimensional analysis is used to analysis factors relative to frictional force. We show that the frictional force scales with where A is the contact area and N is the normal contact force. An experiment is carried out to verify the new friction law.

scholarly journals On the Influence of Microtopography on the Sliding Performance of Cross Country Skis

2021 ◽  
Vol 7 ◽  
Author(s):  
Matthias Scherge ◽  
Melissa Stoll ◽  
Michael Moseler
Keyword(s):  
Grain Size ◽  
Optical Microscopy ◽  
Contact Area ◽  
Contact Surface ◽  
The Real ◽  
Real Area Of Contact ◽  
Surface Topographies ◽  
Freely Moving ◽  
Cross Country ◽  
Real Area

The sliding performance of cross country skis is mainly influenced by the ability of the ski base to minimize capillary forces and contact area. Whereas, the first condition depends on hydrophobicity, the second one is controlled by the ski grinding structure and the morphology of snow. In this contribution the results of sliding tests with five typical grinding structures will be presented and compared to calculations of the real area of contact. Surface topographies were measured and corresponding roughness features were analyzed by 3D optical microscopy. The measured ski base profiles and the measured grain size distribution of granular snow at −2°C were employed within a bearing model for a rough surface in contact with loose and freely-moving snow grains treated as ice spheres. For the five grinding structures, this model revealed a good correlation of the real area of contact between ski and snow with run times in lab-condition sliding tests. The results indicate that the snow-containing volume of the grinding structure is pivotal for tailoring the sliding behavior.

A Study of the Relative Surface Conformity Between Two Surfaces in Sliding Contact

1991 ◽  
Vol 113 (4) ◽  
pp. 755-761 ◽  
Author(s):  
Fu-Xing Wang ◽  
P. Lacey ◽  
R. S. Gates ◽  
S. M. Hsu
Keyword(s):  
Surface Roughness ◽  
Computer Program ◽  
Contact Area ◽  
Sliding Contact ◽  
Test Duration ◽  
Lubrication Mechanism ◽  
The Real ◽  
Wear Process ◽  
Real Area Of Contact ◽  
Real Area

The surface roughnesses of two surfaces in a wear contact can change throughout the course of the wear process. This may or may not change the lubrication mechanism of the system depending on the real area of contact as influenced by the changes in the surface roughness. The present work examines the changes in surface roughness within the contact area, as well as the relative mating of the two surfaces. To quantify the similarity between the two wear surfaces, a new concept, the relative surface conformity, has been defined and developed. To effectively measure this parameter, a computer program was written to input the wear scar profilometry traces and to calculate the relative surface conformity of the two. Finally, the relative surface conformity was shown to rise with increasing test duration, during running in.

Analysis of the Real Area of Contact Between a Polymeric Magnetic Medium and a Rigid Surface

1984 ◽  
Vol 106 (1) ◽  
pp. 26-34 ◽  
Author(s):  
Bharat Bhushan
Keyword(s):  
Complex Modulus ◽  
Critical Value ◽  
Computer Applications ◽  
Hard Material ◽  
Rigid Surface ◽  
Magnetic Medium ◽  
The Real ◽  
Real Area Of Contact ◽  
The Mean ◽  
Real Area

The statistical analysis of the real area of contact proposed by Greenwood and Williamson is revisited. General and simplified equations for the mean asperity real area of contact, number of contacts, total real area of contact, and mean real pressure as a function of apparent pressure for the case of elastic junctions are presented. The critical value of the mean asperity pressure at which plastic flow starts when a polymer contacts a hard material is derived. Based on this, conditions of elastic and plastic junctions for polymers are defined by a “polymer” plasticity index, Ψp which depends on the complex modulus, Poisson’s ratio, yield strength, and surface topography. Calculations show that most dynamic contacts that occur in a computer-magnetic tape are elastic, and the predictions are supported by experimental evidence. Tape wear in computer applications is small and decreases Ψp by less than 10 percent. The theory presented here can also be applied to rigid and floppy disks.

Experimental Validation of a Volumetric Planetary Rover Wheel/Soil Interaction Model

2013 ◽  
Author(s):  
Willem Petersen ◽  
John McPhee
Keyword(s):  
Contact Force ◽  
Interaction Model ◽  
Contact Model ◽  
Soil Parameters ◽  
Model Parameters ◽  
Force Model ◽  
Normal Contact ◽  
Planetary Rover ◽  
Normal Contact Force ◽  
Contact Force Model

For the multibody simulation of planetary rover operations, a wheel-soil contact model is necessary to represent the forces and moments between the tire and the soft soil. A novel nonlinear contact modelling approach based on the properties of the hypervolume of interpenetration is validated in this paper. This normal contact force model is based on the Winkler foundation model with nonlinear spring properties. To fully define the proposed normal contact force model for this application, seven parameters are required. Besides the geometry parameters that can be easily measured, three soil parameters representing the hyperelastic and plastic properties of the soil have to be identified. Since it is very difficult to directly measure the latter set of soil parameters, they are identified by comparing computer simulations with experimental results of drawbar pull tests performed under different slip conditions on the Juno rover of the Canadian Space Agency (CSA). A multibody dynamics model of the Juno rover including the new wheel/soil interaction model was developed and simulated in MapleSim. To identify the wheel/soil contact model parameters, the cost function of the model residuals of the kinematic data is minimized. The volumetric contact model is then tested by using the identified contact model parameters in a forward dynamics simulation of the rover on an irregular 3-dimensional terrain and compared against experiments.

A Relationship Between Autocorrelation Length and Adhesive Friction Behavior of Rough Surfaces

2005 ◽  
Author(s):  
Yilei Zhang ◽  
Sriram Sundararajan
Keyword(s):  
Rough Surface ◽  
Spatial Information ◽  
Roughness Parameter ◽  
Hertzian Contact ◽  
Root Mean Square Roughness ◽  
Friction Behavior ◽  
The Real ◽  
Real Area Of Contact ◽  
Autocorrelation Length ◽  
Real Area

Autocorrelation Length (ACL) is a surface roughness parameter that provides spatial information of surface topography that is not included in amplitude parameters such as Root Mean Square roughness. This paper presents a statistical relation between ACL and the real area of contact, which is used to study the adhesive friction behavior of a rough surface. The influence of ACL on profile peak distribution is studied based on Whitehouse and Archard’s classical analysis, and their results are extended to compare profiles from different surfaces. With the knowledge of peak distribution, the real area of contact of a rough surface with a flat surface can be calculated using Hertzian contact mechanics. Numerical calculation shows that real area of contact increases with decreasing of ACL under the same normal load. Since adhesive friction force is proportional to real area of contact, this suggests that the adhesive friction behavior of a surface will be inversely proportional to its ACL. Results from microscale friction experiments on polished and etched silicon surfaces are presented to verify the analysis.

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