The Effect of Surface Roughness on Static Friction and Junction Growth of an Elastic-Plastic Spherical Contact

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
D. Cohen ◽  
Y. Kligerman ◽  
I. Etsion
Keyword(s):  
Surface Roughness ◽  
Normal Load ◽  
Static Friction ◽  
Threshold Value ◽  
Real Contact Area ◽  
Surface Model ◽  
Spherical Contact ◽  
Elastic Plastic ◽  
Surface Models ◽  
Effect Of Surface

A model for elastic-plastic spherical contact of rough surfaces under combined normal and tangential loadings, with full stick contact condition, is presented. The model allows evaluation of the effect of surface roughness on the real contact area, static friction and junction growth under small normal loads. It is shown that as the normal load approaches a certain threshold value, which depends on the plasticity index, the results of the present rough surface model approach these of previous corresponding models for smooth sphere and a rigid flat. At normal load values below the threshold load, the correlation of the present results and published experimental results is much better in comparison with the results of the smooth surface models.

Static Friction Experiments and Verification of an Improved Elastic-Plastic Model Including Roughness Effects

2007 ◽  
Vol 129 (4) ◽  
pp. 754-760 ◽  
Author(s):  
Chul-Hee Lee ◽  
Andreas A. Polycarpou
Keyword(s):  
Surface Roughness ◽  
Friction Coefficient ◽  
Wear Debris ◽  
Normal Load ◽  
Static Friction ◽  
Displacement Rate ◽  
Experimental Measurements ◽  
Roughness Effects ◽  
Elastic Plastic ◽  
Static Friction Coefficient

An experimental study was conducted to measure the static friction coefficient under constant normal load and different interface conditions. These include surface roughness, dwell time, displacement rate, as well as the presence of traces of lubricant and wear debris at the interface. The static friction apparatus includes accurate measurement of friction, normal and lateral forces at the interface (using a high dynamic bandwidth piezoelectric force transducer), as well as precise motion control and measurement of the sliding mass. The experimental results show that dry surfaces are more dependent on the displacement rate prior to sliding inception compared to boundary lubricated surfaces in terms of static friction coefficient. Also, the presence of wear debris, boundary lubrication, and rougher surfaces decrease the static friction coefficient significantly compared to dry smooth surfaces. The experimental measurements under dry unlubricated conditions were subsequently compared to an improved elastic-plastic static friction model, and it was found that the model captures the experimental measurements of dry surfaces well in terms of the surface roughness.

Experimental Study of Static Friction in a Spherical Elastic-Plastic Contact

2008 ◽  
Author(s):  
Andrey Ovcharenko ◽  
Gregory Halperin ◽  
Izhak Etsion
Keyword(s):  
Friction Force ◽  
Normal Load ◽  
Static Friction ◽  
Tangential Displacement ◽  
Accurate Identification ◽  
Elastic Plastic ◽  
Static Friction Coefficient ◽  
Wide Range ◽  
Material Good ◽  
Contact Diameter

The elastic-plastic contact between a deformable sphere and a rigid flat during pre-sliding is studied experimentally. Measurements of friction force and contact area are done in real time along with an accurate identification of the instant of sliding inception. The static friction force and relative tangential displacement are investigated over a wide range of normal preloads for several sphere materials and diameters. It is found that at low normal loads the static friction coefficient depends on the normal load in breach of the classical laws of friction. The pre-sliding displacement is found to be less than 5 percent of the contact diameter, and the interface mean shear stress at sliding inception is found to be slightly below the shear strength of the sphere material. Good correlation is found between the present experimental results and a recent theoretical model in the elastic-plastic regime of deformation.

scholarly journals An Experimental Study on the Effect of Surface Texture on Contact Stiffness Using Soft Material

2018 ◽  
Vol 217 ◽  
pp. 02005
Author(s):  
Z. Fuadi
Keyword(s):  
Surface Texture ◽  
Normal Load ◽  
Contact Stiffness ◽  
Soft Material ◽  
Contact Dynamics ◽  
Real Contact Area ◽  
Textured Surfaces ◽  
Indentation Force ◽  
Result Show ◽  
Effect Of Surface

Contact interface is one of the most important factors in a mechanical contact because it is the place where friction, sound, and heat originate. It is therefore inevitable that modeling various phenomenon related to contact dynamics requires a proper representation of the contact interfaces. One of the methods in representing the behavior of two surfaces in contact is by using the parameter of contact stiffness. In this study, the effect of surface texture on contact stiffness is analyzed. the texture was used in order to reduce the randomness of surface roughness. the soft material was chosen to achieve a pure elastic contact thus preventing plastic deformation to the asperities. the analysis was conducted by using an indentation method employing a steel ball with a relatively small indentation force. the result show contact stiffness values of the textured surfaces were smaller than that of smooth surface. This is particularly observed at low normal load at which total deformation of the surface is relatively small compared to the asperities height. This decrease in the contact stiffness value of the textured surfaces can be related to the reduction in the real contact area.

Elastic-Plastic Microcontact Analysis of a Sphere and a Flat Plate

2007 ◽  
Vol 23 (4) ◽  
pp. 341-352 ◽  
Author(s):  
J. L. Liou ◽  
J. F. Lin
Keyword(s):  
Surface Roughness ◽  
Flat Plate ◽  
Contact Pressure ◽  
Contact Area ◽  
Normal Load ◽  
Contact Load ◽  
Asperity Contact ◽  
Elastic Plastic ◽  
Deformation Regime ◽  
Maximum Contact

ABSTRACTThe elastic-plastic microcontact model of a sphere in contact with a flat plate is developed in the present study to investigate the effect of surface roughness on the total contact area and contact load. From the study done by the finite element method, the dimensionless asperity contact area, average contact pressure, and contact load in the elastoplastic regime are assumed to be a power form as a function of dimensionless interference (δ/δec). The coefficients and exponents of the power form expressions can be determined by the boundary conditions set at the two ends of the elastoplastic deformation regime. The contact pressures evaluated by the present model are compared with those predicted by the Hertz theory, without considering the surface roughness and the reported model, including the roughness effect, but only manipulating in the elastic regime. The area of non-zero contact pressure is enlarged if the surface roughness is considered in the microcontact behavior. The maximum contact pressure is lowered by the presence of surface roughness if the contact load is fixed. Under a normal load, both the contact pressure and the contact area are elevated by raising the plasticity index for the surface of the same surface roughness.

scholarly journals Evolution of real contact area under shear and the value of static friction of soft materials

2018 ◽  
Vol 115 (3) ◽  
pp. 471-476 ◽  
Author(s):  
R. Sahli ◽  
G. Pallares ◽  
C. Ducottet ◽  
I. E. Ben Ali ◽  
S. Al Akhrass ◽  
...  
Keyword(s):  
Contact Area ◽  
Normal Load ◽  
Scaling Law ◽  
Reduction Rate ◽  
Static Friction ◽  
Soft Materials ◽  
Real Contact Area ◽  
The Real ◽  
Real Contact ◽  
Area Reduction

The frictional properties of a rough contact interface are controlled by its area of real contact, the dynamical variations of which underlie our modern understanding of the ubiquitous rate-and-state friction law. In particular, the real contact area is proportional to the normal load, slowly increases at rest through aging, and drops at slip inception. Here, through direct measurements on various contacts involving elastomers or human fingertips, we show that the real contact area also decreases under shear, with reductions as large as 30%, starting well before macroscopic sliding. All data are captured by a single reduction law enabling excellent predictions of the static friction force. In elastomers, the area-reduction rate of individual contacts obeys a scaling law valid from micrometer-sized junctions in rough contacts to millimeter-sized smooth sphere/plane contacts. For the class of soft materials used here, our results should motivate first-order improvements of current contact mechanics models and prompt reinterpretation of the rate-and-state parameters.

Experimental Study of Adhesive Static Friction in a Spherical Elastic-Plastic Contact

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
A. Ovcharenko ◽  
G. Halperin ◽  
I. Etsion
Keyword(s):  
Friction Force ◽  
Normal Load ◽  
Static Friction ◽  
Tangential Displacement ◽  
Accurate Identification ◽  
Elastic Plastic ◽  
Static Friction Coefficient ◽  
Wide Range ◽  
Material Good ◽  
Contact Diameter

The elastic-plastic contact between a deformable sphere and a rigid flat during presliding is studied experimentally. Measurements of friction force and contact area are done in real time along with an accurate identification of the instant of sliding inception. The static friction force and relative tangential displacement are investigated over a wide range of normal preloads for several sphere materials and diameters. Different behavior of the static friction is observed in the elastic and in the elastic-plastic regimes of sphere deformation. It is found that at low normal loads, the static friction coefficient depends on the normal load in breach of the classical laws of friction. The presliding displacement is found to be less than 5% of the contact diameter, and the interface mean shear stress at sliding inception is found to be slightly below the shear strength of the sphere material. Good correlation is found between the present experimental results and a recent theoretical model in the elastic-plastic regime of deformation.

Pre-Sliding of a Spherical Elastic-Plastic Contact

2008 ◽  
Author(s):  
Andrey Ovcharenko ◽  
Gregory Halperin ◽  
Izhak Etsion
Keyword(s):  
Friction Force ◽  
Normal Load ◽  
Static Friction ◽  
Tangential Displacement ◽  
Accurate Identification ◽  
Elastic Plastic ◽  
Static Friction Coefficient ◽  
Wide Range ◽  
Material Good ◽  
Contact Diameter

The elastic-plastic contact between a deformable sphere and a rigid flat during pre-sliding is studied experimentally. Measurements of friction force and contact area are done in real time along with an accurate identification of the instant of sliding inception. The static friction force and relative tangential displacement are investigated over a wide range of normal preloads for several sphere materials and diameters. It is found that at low normal loads the static friction coefficient depends on the normal load in breach of the classical laws of friction. The pre-sliding displacement is found to be less than 5 percent of the contact diameter, and the interface mean shear stress at sliding inception is found to be slightly below the shear strength of the sphere material. Good correlation is found between the present experimental results and a recent theoretical model in the elastic-plastic regime of deformation.

scholarly journals When the going gets rough – studying the effect of surface roughness on the adhesive abilities of tree frogs

2016 ◽  
Vol 7 ◽  
pp. 2116-2131 ◽  
Author(s):  
Niall Crawford ◽  
Thomas Endlein ◽  
Jonathan T Pham ◽  
Mathis Riehle ◽  
W Jon P Barnes
Keyword(s):  
Surface Roughness ◽  
Real Contact Area ◽  
Small Scale ◽  
Tree Frog ◽  
Natural Habitats ◽  
Litoria Caerulea ◽  
Frictional Forces ◽  
Tree Frogs ◽  
Air Pockets ◽  
Effect Of Surface

Tree frogs need to adhere to surfaces of various roughnesses in their natural habitats; these include bark, leaves and rocks. Rough surfaces can alter the effectiveness of their toe pads, due to factors such as a change of real contact area and abrasion of the pad epithelium. Here, we tested the effect of surface roughness on the attachment abilities of the tree frog Litoria caerulea. This was done by testing shear and adhesive forces on artificial surfaces with controlled roughness, both on single toe pads and whole animal scales. It was shown that frogs can stick 2–3 times better on small scale roughnesses (3–6 µm asperities), producing higher adhesive and frictional forces, but relatively poorly on the larger scale roughnesses tested (58.5–562.5 µm asperities). Our experiments suggested that, on such surfaces, the pads secrete insufficient fluid to fill the space under the pad, leaving air pockets that would significantly reduce the Laplace pressure component of capillarity. Therefore, we measured how well the adhesive toe pad would conform to spherical asperities of known sizes using interference reflection microscopy. Based on experiments where the conformation of the pad to individual asperities was examined microscopically, our calculations indicate that the pad epithelium has a low elastic modulus, making it highly deformable.

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