7 - David Woodward - The static contact patch of some friction … · 2016. 5. 20. · The static...
Transcript of 7 - David Woodward - The static contact patch of some friction … · 2016. 5. 20. · The static...
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The static contact patch of some
friction measuring devices
David Woodward, Phillip Millar,
Chris Tierney and Campbell Waddell
Highway Engineering Research Group
University of Ulster
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This paper
• Tyre / asphalt surface contact patch.
• Influences surface characteristics such as:
– friction, noise, rolling resistance
• Static contact patch of three devices commonly used
around the world to measure highway or airfield
friction:
– the pendulum tester
– GripTester
– SCRIM
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Using paint (ASTM F870-94, 2010)
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Surface contact – are you sitting comfortably?
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Odd one out?
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From paint to pressure mapping
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Pressure mapping
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Toyo v. Avon – rear right @ 20psi
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flat 1psi 3psi 5psi 8psi
10psi 15psi 20psi 25psi 30psi
Formula Student rear slick
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Contact patches for trafficked slabs
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Variation in contact pressures for a
new GripTester tire on 10mm SMA
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Thermal image showing heat transfer
from friction tyre
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Pressure mapping used in this paper
• XSensor IX500.256.256.22 pressure mapping system:– 1.15 mm spatial resolution and 65,536 sensing elements
mounted on a rigid plexi-glass backing.
– Pressure range of 10 – 200 psi
– Data acquisition rate of 6.2 frames per second
• XSENSOR X3 PRO Version 6.0 software records and displays data from the sensor pad.
• Data can be displayed in 2D or 3D.
• Data relating to each of the 65,536 sensing elements can be exported into Excel, CAD or spatial GIS modelling software for further analysis.
• Only contact patch area, length, width and measured load are considered in this paper.
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The pendulum tester
• Wide slider 57 consisting of a rubber pad 76.2 x 25.4 mm as normally used for surfaces subject to vehicular traffic. This is also known as the TRL slider.
• Wide slider 96 consisting of a rubber pad 76.2 x 25.4 mm as normally used for surfaces subject to shoe or foot usage. This is also known as the 4S slider.
• Narrow slider consisting of a rubber pad 31.75 x 25.4 mm as normally used in the PSV test method.
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Wide slider 57 contact patch
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Wide slider 96 contact patch
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Narrow PSV slider contact patch
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GripTester resting on the XSENSOR
pressure pad
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GripTester tyre contact patch at 20 psi
inflation pressure
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Contact length and width v. tyre
inflation pressure for GT tyre
y = 127.63x-0.288
R² = 0.9265
y = -0.0511x + 53.055R² = 0.9834
0
10
20
30
40
50
60
70
0 100 200 300
Dis
tance (
mm
)
Inflation presuure (kPa)
Length
Width
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Contact area v. tyre inflation pressure
for GT tyre
y = 10651x-0.443
R² = 0.9763
0
500
1000
1500
2000
2500
3000
3500
0 100 200 300
Conta
ct
are
a (
mm
2)
Tyre inflation pressure (kPa)
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Contact area v. tyre inflation pressure– excluding lower and higher inflation data
y = -2.5308x + 1537.7R² = 0.9354
0
500
1000
1500
2000
2500
3000
3500
0 50 100 150 200 250
Conta
ct
are
a (
mm
2)
Tyre inflation pressure (kPa)
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SCRIM tyre contact patch
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Some general points:• Pendulum tester:
– Differences between the three rubber sliders
– Contact pressure for the narrow PSV slider was greater than for the 2 wide sliders
– Non-uniform pressure distribution along the width of the three sliders used in the
investigation
• GripTester:
– Relationships similar to previous researchers using other types of tyre
– Main difference between this and previous research was the simplicity and speed of
high quality data acquisition
– The found relationships show contact area and length to behave in a parabolic manner
whereas contact width behaves in a linear manner with tire inflation pressure
• SCRIM:
– Higher contact pressures compared to the GripTester tyre reflecting the greater static
loading and inflation pressure.
– A central rib of higher contact pressure was found for the SCRIM tyre assessed
– How this influences the measurement of friction as the tyre rolls down a road is still to
be determined
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Conclusions
• This paper shows how pressure mapping can help to improve understanding of what happens when a friction measuring device is used.
• Measurement is now relatively easy.
• It does in hours what would take weeks using the paint / card board technique.
• With regard to better understanding and so improvement in any modelling scenario:– these simple examples show how pressure distribution varies
within the contact patch of the measuring device
– they show that measurement or prediction of friction is not simply related to factors such as contact area
• This area needs further research.