Post on 05-Jun-2021
21. April 2015
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Rubber Friction and Tire Dynamics:
A Comparison of Theory with Experimental Data
| Boris Lorenz
Bo Persson
www.MultiscaleConsulting.com
www.MultiscaleConsulting.com
Tire models are often used to simulate the
interactions between the tire and the road.
Most tire models only use a very simple
describtion of the friction at the interface!
This is the weak spot in most tire models
Motivation
Despite of its importance, rubber
friction is still not well understood!
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Energy dissipation because of viscoelastic deformations of the
rubber bulk material when sliding.
Rubber FrictionGeneral Understanding
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Rubber FrictionOn different lengthscales
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Rubber FrictionOn different lengthscales
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Rubber FrictionOn different lengthscales
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e.g. from nanometer � to centimeter
Real surfaces have roughness over a wide range of
lengthscales!!
Taking into account the whole range is impossible using
standard numerical methods like FEM
An analytical approach for our problem is needed
mmmµmnm
Problem in Tribology
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Basic Processes
(Process a) Viscoelastic deformations of the rubber bulk
(Process b) Shearing the contact area
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Rubber Friction Approach
We assume that the sum of a viscoelastic and a contact
area contribution gives the total rubber friction coefficient.
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Measuring TopographyPower Spectrum
Measuring surface roughness along a line using a Profilometer or other methods
From the topography we calculate
the power spectrum:
2
2
)()(
)()(
qhqC
xdexhqhxiq
=
= ∫⋅
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Material PropertiesViscoelastic Modulus
Dynamic Mechanical Analysis (DMA) provides all necesarry
information on the material properties. The complex
viscoelastic Modulus:
)(ωE
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Results for unfilled SB rubber
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Contact Area Contribution
Shearing the contact area:
� attach to the substrate
� get stretched
� detach, dissipating stored up elastic energy
� reattach again
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Tire Tread Rubber
Rubber friction of tread compounds on
road surfaces:
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Wet Rubber Friction
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Temperature Effects
� The dissipated energy at the interface and in the rubber
bulk lead to a heating up of the whole rubber block.
� As rubber friction is very sensitive to temperature.
� Heat transfer to the substrate is taken into account
which is of great impotance.
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Temperature Effects
The rubber undergoes heating effects when moving through the footprint. This
can either be taken into account exactly or interpolated.
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2D Tire Model
We have developed a simple 2D tire model to embed
the friction subroutine:
Rubber blocks are connected by springs and dampers.
The friction model is applied to the individual blocks.
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ABS Breaking Simulations
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Summary
� Rubber friction can only be studied using analytical approaches
� We presented a friction model by Persson including:
� Viscoelastic dissipation
� Contribution from shearing the real area of contact
� Experiments show good agreement between theory and measurements
� We showed that the friction model can be embedded in a tire model describing the frictional
interactions between the tire and the road substrate
Thank you for your attention!
Find more information on our homepage:
www.MultiscaleConsulting.com
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Appendix: Modified Surface Layer
SEM picture of the tread of a car tire after
sliding.
(a) Low magnification
(b) High magnification
Increased concentration of oxygen suggesting
chemicall reactions with the environment and
undergoing oxidation processes during sliding.
The wear layer has very different properties
compared to the bulk material!
N.V. Rodriguez et al., J. Engineering Tribology 227, 398 (2013)
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Appendix: Contact Area Contribution
K.A. Grosch, Proc. R. Soc. Lond. A 274, 21 (1963)
Friction mastercurve of an acrylonitrile-butadiene rubber sliding over a smooth glass substrate.
Energy dissipation is attributed to adhesive interactions between the rubber and the glass in the
contact area