An experimental study on the relation between friction force and real contact area

AbstractClassical laws of friction suggest that friction force is proportional to the normal load and independent of the nominal contact area. As a great improvement in this subject, it is now widely accepted that friction force is proportional to the real contact area, and much work has been conducted based on this hypothesis. In present study, this hypothesis will be carefully revisited by measuring the friction force and real contact area in-site and real-time at both normal loading and unloading stages. Our experiments reveal that the linear relation always holds between friction force and normal load. However, for the relation between friction force and real contact area, the linearity holds only at the loading stage while fails at the unloading stage. This study may improve our understanding of the origin of friction.

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Does Linearity Always Hold between Friction Force and Real Contact Area: An Experimental Study

10.20944/preprints202106.0210.v1 ◽

2021 ◽

Author(s):

Xuan Ming Liang ◽

Yuzhe Xing ◽

Leitao Li ◽

Weike Yuan ◽

G.F. Wang

Keyword(s):

Experimental Study ◽

Friction Force ◽

Contact Area ◽

Normal Load ◽

Real Contact Area ◽

Normal Loading ◽

Real Contact ◽

Loading And Unloading ◽

Nominal Contact Area ◽

Real Area

Classical laws of friction suggest that friction force is proportional to the normal load and independent of the nominal contact area. As a great improvement in this subject, it is now widely accepted that friction force is proportional to the real area in contact, and much work has been conducted based on this hypothesis. In present study, this hypothesis will be carefully revisited by measuring the friction force and real contact area in-site and real-time at both normal loading and unloading stages. Our experiments reveal that the linear relation always holds between friction force and normal load. However, for the relation between friction force and real contact area, the linearity holds only at the loading stage while fails at the unloading stage. This study may improve our understanding of the origin of friction.

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Measurement of Real Contact Area for Rough Metal Surfaces and the Distinction of Contribution From Elasticity and Plasticity

Journal of Tribology ◽

10.1115/1.4048728 ◽

2020 ◽

Vol 143 (7) ◽

Author(s):

Lei-Tao Li ◽

Xuan-Ming Liang ◽

Yu-Zhe Xing ◽

Duo Yan ◽

Gang-Feng Wang

Keyword(s):

Contact Area ◽

Rough Surfaces ◽

Normal Load ◽

Real Contact Area ◽

The Real ◽

Physical Mechanisms ◽

Frustrated Total Internal Reflection ◽

Real Contact ◽

New Apparatus ◽

Elastic And Plastic Deformation

Abstract The measurement of the real contact area between rough surfaces is one of the most challenging problems in contact mechanics and is of importance to understand some physical mechanisms in tribology. Based on the frustrated total internal reflection, a new apparatus is designed to measure the real contact area. For metallic samples with various surface topographies, the relation between normal load and the real contact area is measured. The unloading process is first considered to distinguish the contribution of elasticity and plasticity in contact with rough surfaces. It is found that both elasticity and plasticity are involved throughout the continuous loading process, different from some present understanding and assumptions that they play at different loading stages. A quantitative parameter is proposed to indicate the contribution of plasticity. The present work not only provides an experimental method to measure the real contact area but figures out how elastic and plastic deformation works in contact with rough surfaces.

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Deterministic Contact Model of a Rough Surface Against a Flat-Layered Surface

ASME/STLE 2004 International Joint Tribology Conference, Parts A and B ◽

10.1115/trib2004-64014 ◽

2004 ◽

Cited By ~ 1

Author(s):

H. R. Pasaribu ◽

D. J. Schipper

Keyword(s):

Mechanical Properties ◽

Rough Surface ◽

Contact Area ◽

Indentation Depth ◽

Normal Load ◽

Contact Model ◽

Real Contact Area ◽

Single Asperity ◽

Real Contact ◽

Effective Mechanical Properties

The effective mechanical properties of a layered surface vary as a function of indentation depth and the values of these properties range between the value of the layer itself and of the substrate. In this paper, a layered surface is modelled like a solid that has effective mechanical properties as a function of indentation depth by assuming that the layer is perfectly bounded to the substrate. The normal load as a function of indentation depth of sphere pressed against a flat layered surface is calculated using this model and is in agreement with the experimental results published by El-Sherbiney (1975), El-Shafei et al. (1983), Tang & Arnell (1999) and Michler & Blank (2001). A deterministic contact model of a rough surface against a flat layered surface is developed by representing a rough surface as an array of spherically shaped asperities with different radii and heights (not necessarily Gaussian distributed). Once the data of radius and height of every single asperity is obtained, one can calculate the number of asperities in contact, the real contact area and the load carried by the asperities as a function of the separation.

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

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1706434115 ◽

2018 ◽

Vol 115 (3) ◽

pp. 471-476 ◽

Cited By ~ 50

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.

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Rate-, state-, and pressure-dependent friction model based on the elastoplastic theory

Friction ◽

10.1007/s40544-019-0321-3 ◽

2020 ◽

Vol 8 (4) ◽

pp. 768-783 ◽

Cited By ~ 1

Author(s):

Shingo Ozaki ◽

Takeru Matsuura ◽

Satoru Maegawa

Keyword(s):

Friction Force ◽

Contact Area ◽

Contact Surface ◽

Internal State ◽

Friction Model ◽

Real Contact Area ◽

State Variables ◽

Real Contact ◽

Model Based ◽

Acrylic Plate

AbstractAdhesion is one of essences with respect to rubber friction because the magnitude of the friction force is closely related to the magnitude of adhesion on a real contact area. However, the real contact area during sliding depends on the state and history of the contact surface. Therefore, the friction force occasionally exhibits rate-, state-, and pressure dependency. In this study, to rationally describe friction and simulate boundary value problems, a rate-, state-, and pressure-dependent friction model based on the elastoplastic theory was formulated. First, the evolution law for the friction coefficient was prescribed. Next, a nonlinear sliding surface (frictional criterion) was adopted, and several other evolution laws for internal state variables were prescribed. Subsequently, the typical response characteristics of the proposed friction model were demonstrated, and its validity was verified by comparing the obtained results with those of experiments conducted considering the contact surface between a rough rubber hemisphere and smooth acrylic plate.

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Scale effects on the attachment pads and friction forces in syrphid flies (Diptera, Syrphidae)

Journal of Experimental Biology ◽

10.1242/jeb.204.8.1421 ◽

2001 ◽

Vol 204 (8) ◽

pp. 1421-1431 ◽

Cited By ~ 9

Author(s):

S. Gorb ◽

E. Gorb ◽

V. Kastner

Keyword(s):

Body Mass ◽

Friction Force ◽

Contact Area ◽

Scale Effects ◽

Real Contact Area ◽

Resistance Force ◽

Friction Forces ◽

The Real ◽

Frictional Properties ◽

Real Contact

To test the role of constructional and dimensional factors in the generation of friction force by systems of setose attachment pads, six species of syrphid fly (Platycheirus angustatus, Sphaerophoria scripta, Episyrphus balteatus, Eristalis tenax, Myathropa florea and Volucella pellucens) were studied using light and scanning electron microscopy. Flies were selected according to their various body mass and attachment pad dimensions. Such variables as pad area, setal density, the area of a single setal tip and body mass were individually measured. A centrifugal force tester, equipped with a fibre-optic sensor, was used to measure the friction forces of the pads on a smooth horizontal surface made of polyvinylchloride. Friction force, which is the resistance force of the insect mass against the sum of centrifugal and tangential forces, was greater in heavier insects such as Er. tenax, M. florea and V. pellucens. Although lighter species generated lower frictional forces, the acceleration required to detach an insect was greater in smaller species. The area of attachment pads, setal tip area and setal density differed significantly in the species studied, and the dependence of these variables on body mass was significant. The frictional properties of the material of the setal tips were not dependent on the dimensions of the fly species. Similar results were obtained for the frictional properties of the pulvillus as a whole. Thus, the properties of the secretion and the mechanical properties of the material of the setal tips are approximately constant among the species studied. It is concluded that differences in friction force must be related mainly to variations in the real contact area generated by the pad on the smooth surface. The real contact area can be estimated as the summed area of the broadened setal tips of the pad in contact with the surface. The real contact area depends on such morphological variables as setal density and the area of a single setal tip. Although individual variables vary among flies with different dimensions, they usually compensate such that smaller setal tip area is partially compensated for by higher setal density.

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An incremental equivalent circular contact model for rough surfaces

Journal of Tribology ◽

10.1115/1.4050602 ◽

2021 ◽

pp. 1-16

Author(s):

Gangfeng Wang ◽

Xuan-Ming Liang ◽

Yan Duo

Keyword(s):

Contact Area ◽

Rough Surfaces ◽

Normal Load ◽

Real Contact Area ◽

Contact Radius ◽

Surface Separation ◽

Real Contact ◽

Proposed Model ◽

Geometrical Information ◽

Circular Contact

Abstract The accurate calculation of real contact area between rough surfaces is a key issue in tribology. In this paper, based on the geometrical information of total contact area and the number of contact patches with respect to surface separation, a new method is proposed to determine the relation between real contact area and normal load. The contact of rough surfaces is treated as an accumulation of equivalent circular contacts with varying average contact radius. For a realistic range of separation, the proposed model predicts a linear relation between real contact area and load, and coincides well with direct finite element calculations. Moreover, this model is general and not confined to isotropic Gaussian surfaces.

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Modeling of the Loading–Unloading Contact of Two Cylindrical Rough Surfaces with Friction

Applied Sciences ◽

10.3390/app10030742 ◽

2020 ◽

Vol 10 (3) ◽

pp. 742 ◽

Cited By ~ 1

Author(s):

Honghai Wang ◽

Peng Jia ◽

Liquan Wang ◽

Feihong Yun ◽

Gang Wang ◽

...

Keyword(s):

Fractal Dimension ◽

Contact Area ◽

Fractal Model ◽

Contact Load ◽

Real Contact Area ◽

Curvature Radius ◽

Real Contact ◽

Deformation Stages ◽

Nonlinear Relation ◽

Loading And Unloading

The first fractal model for the loading–unloading process between two cylindrical surfaces with friction is presented. The nonlinear relation between the real contact area and the contact load in different deformation stages are deduced for a load–unload cycle. The impacts of parameters in the model are discussed. The numerical results show that for a given dimensionless contact load, the dimensionless real contact area of the loading–unloading process of cylindrical contact surface with friction, as well as the differences of the dimensionless real contact area between the loading and unloading processes, increase with the increase of the loading interference and fractal dimension, decrease of the profile scaling parameter and curvature radius, or the substitution of external contact for internal contact.

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Effect of normal load on the frictional and wear behaviour of carbon fiber in tow-on-tool contact during three-dimensional weaving process

Journal of Industrial Textiles ◽

10.1177/1528083720944615 ◽

2020 ◽

pp. 152808372094461

Author(s):

Ning Wu ◽

Ximing Xie ◽

Jie Yang ◽

Yajie Feng ◽

Yanan Jiao ◽

...

Keyword(s):

Carbon Fiber ◽

Contact Area ◽

Normal Load ◽

Three Dimensional ◽

Hertzian Contact ◽

Wear Behaviour ◽

Real Contact Area ◽

The Real ◽

Real Contact ◽

Fracture Damage

The effect of normal load on the frictional and wear behaviour of carbon fiber is investigated by simulating the tow-on-tool friction relevant to the beating-up motion of three-dimensional (3 D) weaving process. The true number of contact filaments over a range of normal loads is calculated by characterizing the cross-section parameters of carbon tow. The real contact area is calculated on the basis of the filaments amount by Hertzian contact model. The friction force values obtained from multiplying the real contact area with shear strength are closely with the measured results. The coefficient of friction increases with the increase of normal loads. When the normal load is 250, 400 and 600 mN, the tensile loss rate of the carbon tow after friction test is 6.3%, 23.2% and 42.4% respectively. The filaments reveal multiple fracture damage patterns which are caused by stretching, shearing and compression during the weaving process.

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