rubber friction and tire dynamics · 2018. 11. 17. · rubber friction can only be studied using...

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


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!


Energy dissipation because of viscoelastic deformations of the

rubber bulk material when sliding.

Rubber FrictionGeneral Understanding


Rubber FrictionOn different lengthscales


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


Basic Processes

(Process a) Viscoelastic deformations of the rubber bulk

(Process b) Shearing the contact area


Rubber Friction Approach

We assume that the sum of a viscoelastic and a contact

area contribution gives the total rubber friction coefficient.


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

=

= ∫⋅


Material PropertiesViscoelastic Modulus

Dynamic Mechanical Analysis (DMA) provides all necesarry

information on the material properties. The complex

viscoelastic Modulus:

)(ωE


Results for unfilled SB rubber


Contact Area Contribution

Shearing the contact area:

� attach to the substrate

� get stretched

� detach, dissipating stored up elastic energy

� reattach again


Tire Tread Rubber

Rubber friction of tread compounds on

road surfaces:


Wet Rubber Friction


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.


Temperature Effects

The rubber undergoes heating effects when moving through the footprint. This

can either be taken into account exactly or interpolated.


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.


ABS Breaking Simulations


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:



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)


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

rubber friction and tire dynamics · 2018. 11. 17. · rubber friction can only be studied using...

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