On the Static-Kinetic Friction Transition in Dry Contact of Rough Surfaces

2011 ◽  
Author(s):  
K. Farhang ◽  
D. Segalman ◽  
M. Starr
Keyword(s):  
Large Scale ◽  
Rough Surfaces ◽  
Tangential Force ◽  
Static Friction ◽  
Partial Slip ◽  
Small Scale ◽  
Asperity Contact ◽  
Kinetic Friction ◽  
Tangential Load ◽  
Asperity Contacts

This paper shows that the Mindlin problem involving two spheres in contact under the action of oscillating tangential force can lead to the account of static-kinetic friction transition. In Mindlin’s problem two spheres experience partial slip as a result of application of oscillating tangential load. When the problem is extended to multi-sphere contact, i.e. two rough surfaces, the application of tangential oscillating load results in partial slip for some asperity contacts while others experience full slip. Increase in the amplitude of the oscillating tangential force results in more contacts experiencing full slip, thereby decreasing the number of contacts in parial slip. Constitutive relation proposed by Mindlin at small scale, governing asperity interaction, is used to obtain the large scale slip function through a statistical summation of asperity scale events. The slip function establishes the fraction of asperity contact in full slip. The complement of the slip parameter is a fraction of asperities in partial slip. Through slip function it is shown that it is possible to define a slip condition for the entire surface. The derivation of the slip function allows the account of transition between static friction and kinetic friction.

Static-Kinetic Friction Transition Using a Proposed Slip Function

2008 ◽  
Author(s):  
K. Farhang ◽  
A. Sepehri ◽  
D. Segalman ◽  
M. Starr
Keyword(s):  
Rough Surface ◽  
Large Scale ◽  
Tangential Force ◽  
Elastic Interaction ◽  
Static Friction ◽  
Partial Slip ◽  
Small Scale ◽  
Asperity Contact ◽  
Kinetic Friction ◽  
External Application

This paper considers the contact between two nominally flat rough surfaces. The rough surface interaction is viewed as a multi-sphere elastic interaction which upon external application of a tangential force would exhibit partial or full slip depending on the magnitude of the applied tangential force. Constitutive relation proposed by Mindlin at small scale, governing asperity interaction, is used along with the method proposed by Greenwood and Williamson to obtain the large scale slip function through a statistical summation of asperity scale events. The slip function establishes the fraction of asperity contact in full slip. The complement of the slip parameter is a fraction of asperities in partial slip. Through slip function it is shown that it is possible to define a slip condition for the entire surface. The derivation of the slip function allows the account of transition between static friction and kinetic friction. The use of the slip function is demonstrated in the dynamic response of a block in friction contact at the rough surface interface with a flat wherein the static-kinetic friction transition is correctly addressed.

Microscratci I Test on Carbon Films as Thin as 20 nm

1990 ◽  
Vol 188 ◽  
Author(s):  
T. W. Wu ◽  
A. L. shull ◽  
J. Lin
Keyword(s):  
Acoustic Emission ◽  
Large Scale ◽  
Normal Load ◽  
Tangential Force ◽  
Carbon Films ◽  
Small Scale ◽  
Scale Spallation ◽  
First Occurrence ◽  
20 Nm ◽  
Scratch Tests

ABSTRACTThe capabilities to monitor tangential force and acoustic emission have been added to the microscratch mode of the IBM microindenter. These two new monitoring devices combined with the existing normal loadcell enhance the ability of the microscratch test to measure mechanical properties of thin film materials. As a demonstration of the upgraded microindenter, scratch tests were performed on 11 0nm and 20nm thick carbon films deposited on Si <100> substrates. The scratch morphology was examined by scanning electron microscopy to correlate the mechanical data to corresponding failure mechanisms.In the case of the 110nm film, a brittle type fracture was taking place as the applied normal load exceeded a critical value. All three monitored outputs detected the first occurrence of the spallation ofthe film. In contrast to the thicker film, large scale spallation was not observed for thle 20nm film, and the acoustic emission detector did not show any significant output. An apparent friction coefficient(FR) is defined as the ratio ofthe tangential force to the normal load. FR is determined to be a useful parameter for monitoring the indenter's transition through the coating into the substrate, particularly in the case of small scale fracturing or simple ploughing through types of failure.

Closed-Form Equations for Three Dimensional Elastic-Plastic Contact of Nominally Flat Rough Surfaces

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Ali Sepehri ◽  
Kambiz Farhang
Keyword(s):  
Closed Form ◽  
Contact Force ◽  
Rough Surfaces ◽  
Tangential Force ◽  
Three Dimensional ◽  
Tangential Direction ◽  
Asperity Contact ◽  
Force Component ◽  
Elastic Plastic ◽  
Functional Forms

Approximate closed-form equations governing the shoulder-shoulder contact of asperities are derived based on a generalization by Chang, Etsion, and Bogy. The work entails the consideration of asperity shoulder-shoulder contact in which the volume conservation is assumed in the plastic flow regime. Shoulder-shoulder asperity contact gives rise to a slanted contact force comprising tangential and normal components. Each force component comprises elastic and plastic terms, which upon statistical summation yields the force component for the elastic and plastic forces for the contact of two rough surfaces. Half-plane tangential force due to elastic-plastic contact is derived through the statistical summation of tangential force component along an arbitrary tangential direction. Two sets of equations are found. In the first set of equations the functional forms are simpler and provide approximation of contact force to within 9%. The second set is enhanced equations derived from the first set of approximate equations that achieve an accuracy of within 0.2%.

Contact Mechanics Analysis of a Rubber Piece on a Smooth Plate

2009 ◽  
Author(s):  
Kyosuke Ono
Keyword(s):  
Contact Mechanics ◽  
Elastic Deformation ◽  
Contact Area ◽  
Large Scale ◽  
Glass Plate ◽  
Applied Pressure ◽  
Small Scale ◽  
Asperity Contact ◽  
The Real ◽  
Parameter Values

In order to elucidate contact and friction characteristics of rubbers, numerical analysis of asperity contact mechanics of a rubber piece with a smooth glass plate was carried out on the basis of an asperity contact model that considers van der Waal’s (vdW) pressure. First, by ignoring vdW pressure and the elastic deformation of the mean height surface, asperity contact characteristics were analyzed using the measured Young’s modulus, and surface parameter values that could yield the measured contact area were estimated. Next, asperity contact characteristics were analyzed by considering the vdW pressure and elastic deformation of a rough sphere that is a model of a large-scale asperity having small-scale asperities. It was found that the actual contact area was similar to the measured contact area; this result could not be obtained without assuming an rms asperity height of ∼0.1 μm for the small-scale asperities. It was also found that the friction coefficient decreased with an increase in the applied pressure in the cases where the friction force is proportional to the real area of contact and to the real internal contact pressure.

Effects of Lattice Orientation and Size on Molecular Asperity Contact Models

2009 ◽  
Author(s):  
J. Robert Polchow ◽  
Wei Huang ◽  
Robert L. Jackson
Keyword(s):  
Contact Mechanics ◽  
Molecular Model ◽  
Rough Surfaces ◽  
Minimum Size ◽  
Small Scale ◽  
Asperity Contact ◽  
Lattice Orientation ◽  
Noticeable Effect ◽  
Contact Models ◽  
Number Of Particles

Surface asperities can range widely in size. Therefore it is important to characterize the effect of size and scale on the contact mechanics. This work presents a molecular model of asperity contact in order to characterize small scale asperity contact. The effects of lattice orientation and radius (number of particles) are examined. It appears that lattice orientation has a noticeable effect, but nominally may not be important in the contact of asperities and rough surfaces. The size appears to be important until a certain minimum size is achieved.

Multiscale Modelling of Stick-Slip Transition of Rough (Fractal) Surfaces

2007 ◽  
Vol 539-543 ◽  
pp. 2594-2600
Author(s):  
Bernardino Chiaia ◽  
Mauro Borri-Brunetto
Keyword(s):  
Tangential Force ◽  
Numerical Algorithms ◽  
Critical Force ◽  
Contact Forces ◽  
Smooth Transition ◽  
Partial Slip ◽  
Small Scale ◽  
Stick Slip ◽  
The One ◽  
Slip Transition

The apparent shear strength of rock discontinuities is lower than that of small scale samples. At the same time, the sliding behavior is characterized, in situ, by marked instabilities. Numerical algorithms permit to calculate contact forces at any point, and to describe the stick-slip transition. On the other hand, the critical aspects are not captured by classical theories. Multiscale simulations show that the contact domain between rough surfaces is a lacunar set. This explains the size-dependence of the apparent friction coefficient. By applying an increasing tangential force, the regime of partial-slip comes into play. However, the continuous and smooth transition to fullsliding predicted by the Cattaneo-Mindlin theory is not occurring in real situations. We implement a numerical renormalization group technique, taking into account the redistribution of stress consequent to partial-slip. This permits the critical value of the tangential force to be found. The critical force is less than the one predicted by Coulomb’s theory, and depends on the specimen size and on the topology of the interface.

Three Dimensional Elastic-Plastic Contact of Nominally Flat Rough Surfaces: Approximate Closed-Form Equations

2007 ◽  
Author(s):  
A. Sepehri ◽  
K. Farhang
Keyword(s):  
Closed Form ◽  
Contact Force ◽  
Rough Surfaces ◽  
Tangential Force ◽  
Three Dimensional ◽  
Tangential Direction ◽  
Asperity Contact ◽  
Force Component ◽  
Elastic Plastic ◽  
Form Closure

Approximate closed-form (closure) equations governing the shoulder-shoulder contact of asperities are derived based on a generalization of Chang, Etsion and Bogy (CEB). The work entails the consideration of asperity shoulder-shoulder contact in which volume conservation is assumed in the plastic flow regime. Shoulder-shoulder asperity contact gives rise to a slanted contact force comprising tangential and normal components. Each force component comprises elastic and elastic-plastic terms, which upon statistical summation yields the force component for the elastic and elastic-plastic force for the contact of two rough surfaces. Half-plane tangential force due to elastic-plastic contact is derived through the statistical summation of tangential force component along an arbitrary tangential direction. Two sets of closure equations are found. In the first set of equations the functional forms are simpler and provide approximation of contact force to within nine percent (9%). The second set of closure equations are closed form equations of more complicated form but with accuracy to within 0.2 percent (0.2%).

Finite Element Modeling of Sliding Contact Between Rough Surfaces

2005 ◽  
Author(s):  
L. Pei ◽  
J. F. Molinari ◽  
M. O. Robbins
Keyword(s):  
Large Scale ◽  
Mechanical Design ◽  
Rough Surfaces ◽  
Model Material ◽  
Sliding Contact ◽  
Small Scale ◽  
Contact Algorithm ◽  
Design And Manufacturing ◽  
Critical Issues ◽  
Frictional Forces

Friction and wear are critical issues in mechanical design and manufacturing. As these mechanisms originate at the asperity level, research models increasingly attempt to capture the influence of surface roughness. In this paper, we study the sliding contact between two rough surfaces. We choose silicon as a model material for its wide use in MEMS applications. We implement an update master/slave contact algorithm accounting for periodic boundary conditions. The obtained results shine new light on the link between small-scale contact clusters and frictional forces and wear mechanisms at the large scale.

A Numerical Static Friction Model for Spherical Contacts of Rough Surfaces, Influence of Load, Material, and Roughness

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
W. Wayne Chen ◽  
Q. Jane Wang
Keyword(s):  
Shear Strength ◽  
Rough Surfaces ◽  
Normal Load ◽  
Tangential Force ◽  
Dissimilar Materials ◽  
Static Friction ◽  
Friction Model ◽  
Friction Mechanism ◽  
Upper Limits ◽  
Rough Surface Contact

The relative motion between two surfaces under a normal load is impeded by friction. Interfacial junctions are formed between surfaces of asperities, and sliding inception occurs when shear tractions in the entire contact area reach the shear strength of the weaker material and junctions are about to be separated. Such a process is known as a static friction mechanism. The numerical contact model of dissimilar materials developed by the authors is extended to evaluate the maximum tangential force (in terms of the static friction coefficient) that can be sustained by a rough surface contact. This model is based on the Boussinesq–Cerruti integral equations, which relate surface tractions to displacements. The materials are assumed to respond elastic perfectly plastically for simplicity, and the localized hardness and shear strength are set as the upper limits of contact pressure and shear traction, respectively. Comparisons of the numerical analysis results with published experimental data provide a validation of this model. Static friction coefficients are predicted for various material pairs in contact first, and then the behaviors of static friction involving rough surfaces are extensively investigated.

Small-Scale Science to Large-Scale Profession

2000 ◽  
Vol 45 (4) ◽  
pp. 396-398
Author(s):  
Roger Smith
Keyword(s):  
Large Scale ◽  
Small Scale
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