Frictional behaviour of engineering surfaces in overall lubrication regimes of point contacts

2011 ◽  
Vol 225 (11) ◽  
pp. 1071-1080 ◽  
Author(s):  
S Wang ◽  
Y-Z Hu ◽  
Q-C Tan
Keyword(s):  
Friction Coefficient ◽  
Contact Area ◽  
Area Ratio ◽  
Mixed Lubrication ◽  
Point Contacts ◽  
Friction Behaviour ◽  
True Contact Area ◽  
Contact Area Ratio ◽  
True Contact ◽  
Frictional Behaviour

The aim of the present paper is to study experimentally and numerically the frictional behaviour of engineering surfaces within all lubrication regions of point contacts. For this reason, a numerical solution proposed elsewhere by the current authors, which can predict friction under the different lubrication modes of elastohydrodynamic, mixed, and boundary lubrications, is introduced. Based on a deterministic model of mixed lubrication, the solution was combined with the variation of the lubricating films’ physical state during the transition of lubrication modes. Results show that roughness amplitude has a great effect on the transition of friction regimes. In addition, it is also observed that variation of the friction coefficient has nearly the same trend as the true contact area ratio in the mixed lubrication state. Meanwhile, it is concluded that transverse roughness has better film-forming capacity than longitudinal roughness and thus leads to a lower magnitude of friction coefficient if the operating conditions are the same. Analysis of the mechanism of friction behaviour suggests that the true contact area ratio determines the friction behaviour of engineering surfaces in mixed lubrication. In smooth contacts, the comparison of experiment tests and simulation results suggests that friction variation results from gradual change of the liquid lubricant to solid-like matter with diminishing film thickness.

scholarly journals Critical shoe contact area ratio for sliding on a tennis hard court

2017 ◽  
Vol 232 (2) ◽  
pp. 112-121 ◽  
Author(s):  
John Eric Goff ◽  
Luke Boswell ◽  
Daniel Ura ◽  
Mark Kozy ◽  
Matt J Carré
Keyword(s):  
Friction Coefficient ◽  
Contact Area ◽  
Sliding Friction ◽  
Static Friction ◽  
Area Ratio ◽  
Critical Ratio ◽  
Static Friction Coefficient ◽  
The Creation ◽  
Contact Area Ratio

Dimples have been used in the design of some modern tennis shoe outsoles to enhance sliding ability on hard courts. Experiments were performed with bespoke rubber samples possessing various numbers of holes, which served to simulate dimples in tennis shoe treads. The aim of the research was to assess the effect of contact area on sliding friction. As the ratio of holes to solid rubber increased, a critical ratio was reached whereby the static friction coefficient decreased by more than 11% for tread-to-court pressures comparable to real tennis play. Although this study analyzed bespoke rubber samples and not actual tennis shoe treads, shoe manufacturers should be interested in the existence of a critical dimple ratio that could aid them in the creation of tennis shoes suited for sliding on hard courts.

Friction Characteristics with Pin-on-Disc Friction Test on Microstructured Surface Using Whirling Electrical Discharge Texturing

2014 ◽  
Vol 1017 ◽  
pp. 417-422
Author(s):  
Vitchuda Lertphokanont ◽  
Takayuki Sato ◽  
Masahiro Oi ◽  
Minoru Ota ◽  
Keishi Yamaguchi ◽  
...  
Keyword(s):  
Friction Coefficient ◽  
Electrical Discharge ◽  
Area Ratio ◽  
Mixed Lubrication ◽  
Optimal Conditions ◽  
Friction Test ◽  
Crater Diameter ◽  
Microstructured Surface ◽  
Pin On Disc ◽  
Lubrication Condition

A microstructured surface was created on a steel surface by whirling electrical discharge texturing (WEDT) since it was considered that the microstructures could act as lubricant reservoirs to assist the formation of a lubricating film, resulting in reduced friction. In this study, friction tests under engine oil were carried out over a range of loads and sliding speeds. In addition, the surface characteristics of the microstructured surface were also investigated to optimize the friction characteristics of the textured surface through pin-on-disc friction tests. It was found that under the mixed lubrication condition near the boundary condition, textured surfaces with texture-area ratio of approximately 6% and a mean crater diameter of 35 μm were considered as the optimal conditions for reducing the friction coefficient. However, a texture-area ratio of approximately 4% and a mean crater diameter of 35 μm were considered as the optimal conditions for reducing the friction coefficient under the mixed lubrication condition near the elastohydrodynamic lubrication condition. It was considered that when the normal load decreased, the lubrication region changed from the mixed lubrication condition to the hydrodynamic lubrication condition, which meant that the actual contact surface area decreased. The decrease in the actual contact surface area with decreasing texture-area ratio led to a reduction in the friction coefficient. Finally, it was clarified that the friction coefficient was reduced under the optimized conditions of the microstructured surface through a pin-on-disc friction test.

scholarly journals Evolution of the True Contact Area of Laser Textured Tungsten Under Dry Sliding Conditions

2019 ◽  
Vol 5 ◽  
Author(s):  
Björn Lechthaler ◽  
Georg Ochs ◽  
Frank Mücklich ◽  
Martin Dienwiebel
Keyword(s):  
Contact Area ◽  
Dry Sliding ◽  
True Contact Area ◽  
True Contact

Partial Film Lubrication Characteristics of Inlet Zone in Cold Strip Rolling

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Kuo Fu ◽  
Yong Zang ◽  
Zhiying Gao
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Contact Area ◽  
Friction Stress ◽  
Area Ratio ◽  
Work Zone ◽  
Zone Length ◽  
Inlet Zone ◽  
Pressure Stress ◽  
Contact Area Ratio

According to the average flow Reynolds equation and rolling theory, a partial film lubrication model of inlet zone has been developed. The model mainly simulates and reflects the influence of surface topography on the inlet film thickness and inlet zone length. Based on the surface topography analysis, a method to judge the friction condition was proposed. All the calculation was conducted by a numerical method. The result shows that the transverse stripe increases the inlet film thickness and the inlet zone length, while the longitudinal stripe decreases them. The surface roughness will enhance this effect. The surface roughness and the stripe direction also have a significant influence on the contact area ratio and the distribution of stress and film thickness in work zone. Transverse stripe increases the lubricant film thickness and separates the roll and the sheet with a larger distance in work zone. It also decreases the contact area ratio, the pressure stress and friction stress of the work zone. Whereas longitudinal stripe decreases the film thickness and increases the contact area ratio, pressure stress and friction stress. The surface roughness increases the contact area ratio, pressure stress and friction stress.

scholarly journals Sliding-induced adhesion of stiff polymer microfibre arrays. I. Macroscale behaviour

2008 ◽  
Vol 5 (25) ◽  
pp. 835-844 ◽  
Author(s):  
Jongho Lee ◽  
Carmel Majidi ◽  
Bryan Schubert ◽  
Ronald S Fearing
Keyword(s):  
Elastic Modulus ◽  
Contact Area ◽  
Shear Force ◽  
Contact Region ◽  
Pure Shear ◽  
Shear Loading ◽  
High Shear ◽  
Polypropylene Fibres ◽  
True Contact Area ◽  
True Contact

Gecko-inspired microfibre arrays with 42 million polypropylene fibres cm −2 (each fibre with elastic modulus 1 GPa, length 20 μm and diameter 0.6 μm) were fabricated and tested under pure shear loading conditions, after removing a preload of less than 0.1 N cm −2 . After sliding to engage fibres, 2 cm 2 patches developed up to 4 N of shear force with an estimated contact region of 0.44 cm 2 . The control unfibrillated surface had no measurable shear force. For comparison, a natural setal patch tested under the same conditions on smooth glass showed approximately seven times greater shear per unit estimated contact region. Similar to gecko fibre arrays, the synthetic patch maintains contact and increases shear force with sliding. The high shear force observed (approx. 210 nN per fibre) suggests that fibres are in side contact, providing a larger true contact area than would be obtained by tip contact. Shear force increased over the course of repeated tests for synthetic patches, suggesting deformation of fibres into more favourable conformations.

FEM Analysis of Hydrostatic Pressure Generated Within Lubricant Entrapped Into Pocket on Workpiece Surface in Upsetting Process

1999 ◽  
Vol 122 (4) ◽  
pp. 822-827 ◽  
Author(s):  
Akira Azushima
Keyword(s):  
Hydrostatic Pressure ◽  
Contact Area ◽  
Plastic Material ◽  
Quantitative Relationship ◽  
Normal Pressure ◽  
Area Ratio ◽  
Real Contact Area ◽  
Bulk Deformation ◽  
Rigid Plastic ◽  
Contact Area Ratio

In order to investigate into the quantitative relationship between the hydrostatic pressure generated within the surface pocket of the workpiece and the normal pressure acting on the real contact area at the interface of metal forming such as drawing, rolling, forging and so on, the hydrostatic pressure is calculated accompanied with reduction in height in upsetting of cylinders having a central conical impression or a central conical dent filled with lubricant on the top surface, using the rigid-plastic finite element method. The formulated is based on the plasticity theory. The material is assumed to be rigid perfectly plastic material. It is assumed that the hydrostatic pressure is generated accompanied with a volume change in the surface pocket for compressible lubricants. The results obtained from the calculation are as follows: (1) The hydrostatic pressure generated within the lubricant in a central conical impression in cylindrical upsetting approaches the yield stress at a reduction in height of about 4 percent; (2) The hydrostatic pressure generated within the lubricant in a central conical dent in cylindrical upsetting having an annular asperity increases linearly and abruptly with increasing height reduction when the contact area ratio is small and the bulk deformation is elastic, and it increases gradually and the maximum value approaches the normal pressure acting on the contact area when the contact area ratio becomes large and the bulk deformation is plastic. [S0742-4787(00)00503-8]

The Role of Diffusion of Polymer Chains in the Mechanism of Adhesion and Autohesion of Rubbers

1957 ◽  
Vol 30 (3) ◽  
pp. 837-846 ◽  
Author(s):  
B. V. Deryagin ◽  
S. K. Zherebkov ◽  
A. M. Medvedeva
Keyword(s):  
Mechanical Properties ◽  
Double Layer ◽  
Contact Area ◽  
Electric Double Layer ◽  
Contact Time ◽  
Diffusion Processes ◽  
The Other ◽  
Shearing Strength ◽  
True Contact Area ◽  
True Contact

Abstract 1. The researches so far published on the autohesion of polymers do not make it possible to isolate the influence of the mechanical properties of rubbers, which determine the true area of contact, from the influence of polymer chain diffusion. 2. Studies of the autohesion of thin films of rubber applied by the drain-off method to quartz threads, in relation to the film thickness and contact time, show that for films less than 3.10−5 cm. thick the adhesion force is small and varies very little with contact time. This proves, on the one hand, that in this instance the contact area is small (which is obvious) and does not increase with time, and on the other hand, that diffusion processes play no part in the autohesion of films of this thickness. 3. The effects which depend on mechanical properties and on the specific interaction (per unit area of true contact) between specimens may be separated if the measured values of adhesion between all possible combinations of pairs of rubbers are compared both with their compatibilities, and with their autohesion. 4. The measurements of the adhesional shearing strength of combinations of different pairs of polymers, carried out for this purpose, showed that the results for Butyl rubber may be interpreted on the assumption that diffusion processes do not play any appreciable role and that the adhesion strength is determined both by the true contact area, which depends on the mechanical properties of the corresponding polymer specimens, and also by the influence of forces associated with the electric double layer. 5. For the other rubbers the results may be interpreted only on the assumption that diffusion processes play a significant part. For similar polarities, T12/T11>1 and for dissimilar polarities, T12/T11<1. 6. General conclusion : autohesion and mutual adhesion of rubbers is determined both by mechanical properties, which determine the true contact area, and by diffusional properties. The latter are by no means always decisive. The electric double layer also probably influences the adhesional shearing strength in some instances. It is even more likely to play a role in some cases in measurements of the work of separation of two layers.

A fractal model of contact between rough surfaces for a complete loading–unloading process

2020 ◽  
Vol 234 (14) ◽  
pp. 2923-2935
Author(s):  
Yuan Yuan ◽  
Kuo Xu ◽  
Ke Zhao
Keyword(s):  
Size Distribution ◽  
Contact Area ◽  
Rough Surfaces ◽  
Contact Process ◽  
Distribution Functions ◽  
Contact Load ◽  
Elastic Behavior ◽  
Loading Process ◽  
True Contact Area ◽  
True Contact

The mechanical properties of contact between rough surfaces play an important role in the reliability of the electromechanical system. In order to improve the design accuracy of precision instruments, an elastic-plastic contact model for three-dimensional rough surfaces based on the fractal theory is developed for a complete loading–unloading process based on the Majumdar and Bhushan model. The truncation size distribution functions of asperities for different values of asperity level in the loading process are given. Relationships between true contact area and total contact load in the complete loading–unloading process are obtained according to the truncation size distribution functions of asperities. The results show the range of asperity levels has significant effects on contact mechanical behaviors of fractal rough surfaces. When the first six levels of asperities do not exceed the critical elastic level, the fractal rough surfaces exhibit elastic behavior in a complete contact process, and the load–area relationships in the loading and unloading processes are coincident approximately. When the critical elastic level is less than the minimum level of asperity, the inelastic deformation begins to appear in fractal rough surfaces and the true contact area during the unloading process is always greater than the true area during the loading process for a given total contact load. In comparison with the K-K-E model, the present model is proved to be reasonable.

Sign in / Sign up

Export Citation Format

Share Document