Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover
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![Page 1: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/1.jpg)
Stefan Ripka, Hagen Lind,Matthias Wangenheim, University Hannover
Klaus Wiese, Burkhard Wies, Continental
Akron, 20.09.2010
Investigation of friction mechanisms of siped tire tread blocks on snowy and icy surfaces
![Page 2: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/2.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Agenda
• Introduction and motivation
• The high speed linear test rig “HiLiTe”
• Set up
• Validation with outdoor tests
• Friction mechanisms on ice
• Basics
• Measurements and Interpretation
• Conclusion
![Page 3: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/3.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Introduction and motivation
• Decreasing friction potential of the road results in an increasing probability of accident
• Reduction of development costs by
• Understanding relevant friction mechanisms of tread blocks on ice and snow
• Transfer of tests to the all year available lab
Source: Continental
• Winter tires gain more and more attention due to safety reasons
Rising requirement of customers concerning tire performance
Effort of the tire industry for improving the tire characteristics
![Page 4: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/4.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Introduction and motivation
• ABS system makes sure that the slip of a tire is reduced to a minimum
Cornering forces can still be transmitted to the ground
• But there is still a zone left, where the tire slips over the road surface!
• During a braking manoeuvre a wide range of sliding velocities can thus be observed
Test rig needs to cover a wide parameter range for closer investigations
![Page 5: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/5.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
High speed linear test rig „HiLiTe“• Bedding on concrete block
(m = 3 t) and styrofoam
• Powered by synchronous servo motor (T = 125 Nm)
• Travelling carriage is driven with tooth belt and performs linear motion
• Challenge: Compromise between mechanical stability and weight
Bedding
Carriage
Synchronous servo motor
Test Track
Tooth belt Rectangularprofile
![Page 6: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/6.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
High speed linear test rig „HiLiTe“
Friction surfaces
• Glass / Corundum (different grid)
• Asphalt / Concrete
• Ice / Snow
Additional equipment:
• IR-camera
• High speed camera
Design Parameters
• Rubber sample: Tread block
• Sliding velocity v = 0.1 … 10 m/s
• Normal force FN = 23 … 1000 N
• Length of friction surface l = 5 m
• Located in environmental chamber
Temperature T = -25 °C … + 60 °C
![Page 7: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/7.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Evaluation of measurements
• Steady state time interval is characterized by constant velocity
• Friction coefficient µ(t) is calculated for each time step from friction force FR(t) divided by normal force FN(t)
• Characteristic friction coefficient is calculated via the average of the steady state time interval of µ(t)
![Page 8: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/8.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Basic friction mechanisms on ice
• Dry run in area of tread block Due to friction energy P ice is heated up Liquid layer:
• Friction force FR consists of dry friction Fd and viscous friction Fv
• Length of dry area depends on friction energy Influenced by sliding velocity v, normal force FN, temperature T, …
• Low friction level on ice caused by viscous friction due to liquid layer
vFP R
h
AvApµFFF wetdrydryvdR
![Page 9: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/9.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Compound evaluation with HiLiTe on ice
• Comparison of different tread compounds (Ref, A, B, C, D): HiLiTe vs. Outdoor
• Outdoor test: car is accelerated, acceleration and slip are measured, µ-slip curve is calculated and evaluated
• Indoor test: Several runs of each sample with different sliding velocities
• Best fit of results for a sliding velocity of v= 5 m/s but correct ranking of compounds for all sliding velocities
Compound evaluation is velocity independent (Different friction levels at higher velocities caused by reduction of adhesion / dry friction zone)
![Page 10: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/10.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Pattern evaluation with HiLiTe on ice
• In general siped winter tires show better performance on ice than non siped tires (for standard winter compounds)
• Investigation of pattern effects with HiLiTe: Siped (G3) vs. non siped (G0) sample for different compounds (REF, A, B, C, D)
• A ratio larger than 100% means a higher friction coefficient for siped block
Pattern effects on ice depend on sliding velocity (increasing velocity increasing friction power increasing liquid layer, decreasing dry friction zone decreasing viscous friction force
• Sipes interrupt liquid layer new dry friction higher friction coefficient for siped samples or winter tires
Source: Continental
G0
G3
![Page 11: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/11.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Flexible Treadblock
• Allows flexible arrangement of block elements
• Allows bordering single angles of block elements
• Different distances can be created
• Holder can be turned (0-360°) side forces can be measured as well
![Page 12: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/12.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Variation of fixing method of tread elements
• Blocked tread block sample: No element deformation can occur
• Clamped sample: Simulation of bending deformation only
• Friction coefficient is significantly influenced by fixing method of sample
• Reason for significant difference becomes clear analyzing the contact area
![Page 13: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/13.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Evaluation of dynamic contact area on ice: Test set up
• Tread block sample is observed while sliding on ice
• Clear ice surface to observe the tread block sample from the bottom up
• Ice surface is prepared on glass
• Camera takes picture from contact area
Detailed analysis of contact area size possible
Camera
HiLiTe carriage
Glass surface with ice layer
![Page 14: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/14.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Investigation of dynamic contact area
FN=72N, v=0,1m/s, µ=1,38 FN=72N, v=0,1m/s, µ=0,4
1 bar 3 bar
ca. 22% ca. 38%• Comparison of different contact areas (bordered (grey) vs. 20°
clamped block element (black)) during friction measurement on ice at two different pressures
• Significant differences of contact area size can be observed!
Clamped sample shows 60-80% smaller contact area size
• Significant influence of the contact area on the friction process: Higher local pressure higher friction energy density increasing liquid layer, decreasing dry friction zone decreasing friction coefficient
![Page 15: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/15.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Pressure dependence of friction coefficient
• With different fixing methods of block sample overall friction characteristic can be calculated
• Contact pressure is calculated from global vertical load and contact area: non deformed sample (p1=1 bar and p2=3 bar)
clamped sample (p3=4,5 bar and p4=7,9 bar)
• Friction coefficient (from clamped sample) fits into global decreasing pressure characteristic
Local pressure and therefore contact area size influence friction process significantly
G0
![Page 16: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/16.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Conclusion
FN=72N, v=0,1m/s, µ=1,38 FN=72N, v=0,1m/s, µ=0,4
• The friction level of the road has a significant influence on the accident probability
• High speed linear test rig allows investigating typical pressures and sliding velocities which prevail at passenger car tires
• Basic tread block friction mechanisms on ice have been introduced
• The validation of HiLiTe measurements on ice with outdoor traction test was successful
• A method for analyzing the contact area during the sliding process was presented
• The influence of the contact area on the friction process of tread block elements was demonstrated and explained
![Page 17: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/17.jpg)
Stefan RipkaInstitut für Dynamik und SchwingungenGottfried Wilhelm Leibniz Universität HannoverAppelstraße 11, 30167 Hannover
www.ids.uni-hannover.de
Thank you for your attention !
![Page 18: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/18.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Comparison of frictional properties of in house vs. natural snow
• In the measured velocity range friction coefficient is relatively constant compared to ice friction
Dominant friction effect is snow milling which can be observed on natural and in house snow
• Differences of friction level results from different surface hardness (from sintering process of the snow)
2 cm
• PC-traction measurements from outside with similar tread pattern show same result: Traction force is nearly constant over a wide slip range
natural snow
(CTI=90, =525kg/m³)
in house produced snow
(CTI=92, =510kg/m³)
![Page 19: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/19.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Influence of tread elements run out area
• Neighbored elements / elements width influence friction on ice:
Last element slides on track heated up by first element
Back part of larger elements slides on liquid layer
• Differences between single element configurations caused by different block element widths resulting in different contact areas
Liquid layer reduces friction potential
Optimum block width can be found
![Page 20: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/20.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Siped tread block model - Requirements -
• Properties of tread block elements:
– length and depth
– mass, stiffness, damping
– 3D - model needs additional block width
• Number of sipes
• Distance between single elements possibility to generate two neighboured blocks
• Friction within the sipe
• Less computational effort compared to FEA
Output parameter: Deformation angle of each block element
![Page 21: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/21.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Siped tread block model-Timoshenko beam
• Timoshenko beam considers longitudinal (x, u) andtransversal (z,w) movement, also includes shear deformation
• Contact problems (bar-bar/bar-surface) solved via penalty method
• The friction Force FR is calculated via the law of Coulomb, friction coefficient µ can be adopted to every friction characteristic
• Friction characteristic considers all friction phenomena like pressure and velocity dependence, contact area, surface material and surface texture
![Page 22: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/22.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Simulation results of Timoshenko beam model
• Simulation result for a beam with d = 6 mm and l = 4 mm
• After the run-in process the steady state of the transversal and longitudinal deflection as well as the shear angle can be observed
• Transversal deflection w 0,9 mm matches very well in experiment and simulation
• Shear angle b 1,7 ° is much too small Tire tread specific parameters for simulation to be defined in the future
In general the Timoshenko beam provides a satisfying approach for simulating the bending angle of single tread blocks
![Page 23: Stefan Ripka, Hagen Lind, Matthias Wangenheim, University Hannover Klaus Wiese, Burkhard Wies, Continental Akron, 20.09.2010 Investigation of friction.](https://reader036.fdocuments.us/reader036/viewer/2022062314/56649eac5503460f94bb2f9b/html5/thumbnails/23.jpg)
© 2010 Stefan Ripka, Leibniz Universität Hannover
Tread block mechanics on ice and snow
Introduction and motivation
• Winter tires gain more and more attention due to safety reasons
Rising requirement of customers concerning tire performance
Effort of the tire industry for improving the tire characteristics
• Reduction of development costs by
• understanding relevant friction mechanisms of tread blocks on ice and snow
• Transfer of tests to the all year available lab
Source: Continental