Effects of Contact Pressure on the Coefficient of Friction in Friction Tests

2003 ◽  
Author(s):  
Kang Xu
Keyword(s):  
Contact Pressure ◽  
Coefficient Of Friction ◽  
The Coefficient Of Friction

scholarly journals Contact pressure and sliding velocity ranges in sheet metal forming simulations

2021 ◽  
Author(s):  
Joseba Cillaurren ◽  
Lander Galdos ◽  
Mario Sanchez ◽  
Alaitz Zabala ◽  
Eneko Saenz de Argandoña ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Contact Pressure ◽  
Sheet Metal ◽  
Coefficient Of Friction ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Sliding Velocity ◽  
Wide Range ◽  
The Coefficient Of Friction ◽  
Friction Models

In the last few years many efforts have been carried out in order to better understand what the real contact between material and tools is. Based on the better understanding new friction models have been developed which have allowed process designers to improve numerical results in terms of component viability and geometrical accuracy. The new models define the coefficient of friction depending on different process parameters such as the contact pressure, the sliding velocity, the material strain, and the tool temperature. Many examples of the improvements achieved, both at laboratory scale and at industrial scale, can be found in the recent literature. However, in each of the examples found in the literature, different ranges of the variables affecting the coefficient of friction are covered depending on the component analysed and the material used to produce such component. The present work statistically analyses the contact pressure and sliding velocity ranges achieved during numerical simulation (FEM) of sheet metal forming processes. Nineteen different industrial components representing a high variety of shapes have been studied to cover a wide range of casuistic. The contact pressure and sliding velocity corresponding to typical areas of the tooling have been analysed though numerical simulation in each case. This study identifies the ranges of contact-pressure and sliding velocities occurring in sheet metal forming aimed to set the characterization range for future friction studies.

On the Mechanics of Crack Initiation and Propagation in Elasto-Plastic Materials in Impact Fretting Wear

2004 ◽  
Vol 126 (2) ◽  
pp. 395-403 ◽  
Author(s):  
Y. B. Gessesse ◽  
M. H. Attia
Keyword(s):  
Crack Initiation ◽  
Contact Pressure ◽  
Coefficient Of Friction ◽  
Contact Area ◽  
Plastic Material ◽  
Oblique Impact ◽  
Fretting Wear ◽  
Isotropic Hardening ◽  
Friction Forces ◽  
The Coefficient Of Friction

Normal and oblique impact wear processes are characterized by unique features, which include the development of some residual stress components that vanish in unidirectional sliding. Parametric finite element analyses were conducted to estimate the likelihood locations for crack initiation, and the subsequent direction and rate of crack propagation in an elasto-plastic material with bi-linear isotropic hardening properties. The results showed that the increase in contact pressure can cause a significant increase in the size of the plastically deformed crack initiation zone and allows it to reach the surface. Such behavior is not predicted under continuous sliding conditions. The presence of surface friction forces in oblique impact, can also result in the development of a secondary region of high tensile stresses at the contact area. Using the crack tip slip displacement CTSD method, the rate of crack growth was found to be linearly proportional to the crack length, and significantly dependent on the contact pressure and the coefficient of friction at the crack surface. The small effect of the coefficient of friction at the micro-contact area on wear suggests that the effect of shear traction is mainly due to the increase in the depth of the crack nucleation zone. As expected, the increase of the material flow stress with strain-hardening has a wear reducing effect.

Determination of the Coefficient of Friction of Rubber at Realistic Tire Contact Pressures

1987 ◽  
Vol 60 (5) ◽  
pp. 966-974 ◽  
Author(s):  
J. J. Lazeration
Keyword(s):  
Surface Roughness ◽  
Contact Pressure ◽  
Coefficient Of Friction ◽  
Pressure Dependence ◽  
High Pressures ◽  
Prediction Models ◽  
Ground Glass ◽  
Normal Contact ◽  
Full Field ◽  
The Coefficient Of Friction

Abstract The rotational friction test effectively eliminated the severe normal contact pressure gradients inherent to many of the conventional test apparatus. The uniform pressure distribution of the annular test specimen, confirmed by Fuji pressure-sensitive paper, provided a pointwise value of the coefficient of friction essential to full-field traction and wear prediction. Models of the form μ=AP−1/k as predicted by true contact area and elasticity theory gave excellent correlation to experimental data and showed that, at high pressures, the value of μ can vary significantly from its value at the average contact pressure acting on the tire. A decrease in the pressure dependence of μ with increasing surface roughness was observed by investigating μ on plexiglass, ground glass, and machined steel substrates. A pressure dependence of P−1/2 for plexiglass, P−1/4 for ground glass, and P−1/5 for machined steel was determined. The surface roughness of both the rubber and the test substrate were found to influence the magnitude and pressure dependence of μ. Consequently, care must be taken with sample preparation for reproducibility and simulation of an actual tread surface if tire performance predictions are to be made.

Contact mechanics of metal-on-metal hip implants employing a metallic cup with a UHMWPE backing

2003 ◽  
Vol 217 (3) ◽  
pp. 207-213 ◽  
Author(s):  
F Liu ◽  
Z M Jin ◽  
P Grigoris ◽  
F Hirt ◽  
C Rieker
Keyword(s):  
Pressure Distribution ◽  
Contact Mechanics ◽  
Contact Pressure ◽  
Coefficient Of Friction ◽  
Hip Implants ◽  
Cobalt Chromium ◽  
Acetabular Cup ◽  
Metal On Metal ◽  
Interfacial Boundary ◽  
The Coefficient Of Friction

The contact mechanics in metal-on-metal hip implants employing a cobalt chromium acetabular cup with an ultra-high molecular weight polyethylene (UHMWPE) backing were analysed in the present study using the finite element method. A general modelling methodology was developed to examine the effects of the interfacial boundary conditions between the UHMWPE backing and a titanium shell for cementless fixation, the coefficient of friction and the loading angle on the predicted contact pressure distribution at the articulating surfaces. It was found that the contact mechanics at the bearing surfaces were significantly affected by the UHMWPE backing. Consequently, a relatively constant pressure distribution was predicted within the contact conjunction, and the maximum contact pressure occurred towards the edge of the contact. On the other hand, the interfacial boundary condition between the UHMWPE backing and the titanium shell, the coefficient of friction and the loading angle were found to have a negligible effect on the contact mechanics at the bearing surfaces. Overall, the magnitude of the contact pressure was significantly reduced, compared with a similar cup without the UHMWPE backing. The importance of the UHMWPE backing on the tribological performance of metal-on-metal hip implants is discussed.

FORMULATION OF TOOL WEAR LAW WHEN CUTTING POLYMER COMPOSITES

2021 ◽  
pp. 36-45
Author(s):  
G. Khavin
Keyword(s):  
Wear Rate ◽  
Tool Wear ◽  
Contact Pressure ◽  
Tool Life ◽  
Coefficient Of Friction ◽  
Rear Surface ◽  
Shear Stresses ◽  
The Coefficient Of Friction ◽  
Wear Law ◽  
Over Time

Numerous experimental studies in the field of mechanical processing of composite materials for individual materials and tools made it possible to formulate particular models for describing tool wear, changing its microgeometry during operation and predicting durability. There are significant difficulties in measuring current wear and recalculation in mathematical models, since they include a large number of parameters. This does not allow for simple technical control of cutting edge wear and predicting tool life. The formulation of the wear-contact problem of the tool tip and the material interaction during turning of reinforced composite plastics is presented. Based on known studies, it is assumed that wear occurs along the flank of the tool, and is accompanied by an asymmetric change in the geometry of its tip. A model of abrasive wear during sliding of a tool tip rear surface with a polymer composite reinforcement material and fracture products is considered. It is assumed that the wear law is hereditary and there is a linear dependence of the wear rate on the rate of contact interaction and pressure. Shear stresses through the contact pressure and the coefficient of friction nonlinearly depend on the operating time of the tool due to the change due to wear in the geometric shape of the tool and the processing parameters of the product over time. The volumetric wear factor is a tool run time function. It reflects the fact that the interaction of the “tool-workpiece” pair with time should, as it were, forget about the running-in stage, which has a high wear rate, and the fact that the dependence of wear on the load (contact pressure) is characterized by the presence of aftereffect. A simplified relationship is obtained for the wear law under the assumption that there is no change in the coefficient of friction, temperature and contact pressure over time. Ultimately, to describe the wear law and predict the tool life, it is necessary to know a number of empirical constants, the values of which are determined by the change in the microgeometry of the tool tip during interaction during cutting.

scholarly journals The Influence of the Contact Pressure on the Value of the Coefficient of Friction

2017 ◽  
Vol 39 (2) ◽  
pp. 255-259 ◽  
Author(s):  
I. Bijelić ◽  
N. Mor ◽  
M. Živković ◽  
V. Tubin ◽  
T. Stožinić
Keyword(s):  
Contact Pressure ◽  
Coefficient Of Friction ◽  
The Coefficient Of Friction

scholarly journals A Study of the Coefficient of Friction in Steel Sheets Forming

Metals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 988 ◽  
Author(s):  
Tomasz Trzepiecinski
Keyword(s):  
Contact Pressure ◽  
Coefficient Of Friction ◽  
Tribological Properties ◽  
Steel Sheet ◽  
Rolling Direction ◽  
Tension Test ◽  
Drawing Test ◽  
Strip Drawing ◽  
The Coefficient Of Friction ◽  
Bending Under Tension

The aim of this paper was to compare the tribological properties of a deep drawing quality steel sheet using the three commonly used friction tests, i.e., the strip drawing test, draw bead test, and bending under tension test. All tests have been carried out using a specially designed friction simulator. The test material was a 0.8-mm-thick DC04 steel sheet, commonly used in the automotive industry. Uniaxial tensile tests have been carried out to characterise the mechanical properties of the specimens. Furthermore, measurements of the sheet surface topography have been carried out to characterise the tribological properties of the specimens. The friction tests have been conducted under different pressure and lubrication conditions, surface roughnesses of tools represented by counter-samples, and orientations of the specimens according to the direction of the sheet rolling. A comparative analysis of the results of the friction tests revealed different values of friction. In the strip drawing test, the value of the coefficient of friction decreases as the contact pressure increases for both dry and lubricated conditions. In the draw bead test, the specimens oriented along the rolling direction demonstrated a higher value of the coefficient of friction compared to the samples cut transverse to the rolling direction. In contrast to the strip drawing test, the specimens tested in the bending under tension test exhibit a tendency to an increase in the value of the coefficient of friction with the increasing contact pressure.

scholarly journals A finite element analysis (FEA) approach to simulate the coefficient of friction of a brake system starting from material friction characterization

Friction ◽  
2020 ◽  
Vol 9 (1) ◽  
pp. 191-200
Author(s):  
Gabriele Riva ◽  
Francesco Varriale ◽  
Jens Wahlström
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Contact Pressure ◽  
Coefficient Of Friction ◽  
Brake System ◽  
Bench Test ◽  
Sliding Velocity ◽  
Element Analysis ◽  
The Coefficient Of Friction ◽  
Brake Force

Abstract The coefficient of friction (COF) is one of the most important parameters to evaluate the performance of a brake system. To design proper brake systems, it is important to know the COF when estimating the brake force and resulting torque. It is challenging to simulate the COF since friction in disc brakes is a complex phenomenon that depends on several parameters such as sliding velocity, contact pressure, materials, and temperatures, etc. There is a lack of studies found in the literature focusing on simulation of the COF for a full brake system based on tribometer material characterization. The aim of this work is therefore to investigate the possibility to use a finite element analysis (FEA) approach combined with a COF pv-map to compute the global COF of a disc brake system. The local COF is determined from a pv-map for each local sliding velocity and contact pressure determined by the FEA. Knowing the local COF, the braking force of the entire brake system and the global COF can be evaluated. Results obtained by the simulation are compared with dyno bench test of the same brake system to investigate the validity of the simulation approach. Results show that the simulation is perfectly in line with the experimental measurements in terms of in-stop COF development, but slightly higher with a positive offset for every braking.

Friction and Wear Behavior of Graphite-Carbon Short Fiber Reinforced Al–17%Si Alloy Hybrid Composites

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
C. S. Ramesh ◽  
T. B. Prasad
Keyword(s):  
Contact Pressure ◽  
Coefficient Of Friction ◽  
Hybrid Composite ◽  
Friction And Wear ◽  
Hybrid Composites ◽  
Matrix Alloy ◽  
Short Fiber ◽  
Wear Rates ◽  
The Matrix ◽  
The Coefficient Of Friction

Graphite and carbon short fiber (copper coated) reinforced (2 wt %) hypereutectic Al–17%Si alloy composites were prepared by liquid metallurgy route. Room temperature friction and wear properties of as-cast hypereutectic Al–Si alloy reinforced with copper coated graphite and short carbon fibers were investigated. Friction and wear tests were conducted using a pin-on-disk machine under dry sliding conditions. The loads (contact pressure) and sliding velocities have been varied from 10 N to 50 N (contact pressure of 0.12–0.60 MPa) and 0.3 m/s to 1.2 m/s, respectively. The results reveal that the coefficient of friction and the wear rate of the hybrid composite are lower than that of the matrix alloy. The coefficient of friction of the matrix alloy and its hybrid composite decreased with increased load of up to 30 N and increased beyond this load. The wear rates of both the matrix alloy and its hybrid composite increased with the increasing load. However, at all the loads and sliding velocities studied, the developed hybrid composite exhibited a lower coefficient of friction and wear rates when compared with the matrix alloy.

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