1. 1
The Effect of Load on Tyre Temperature and
Contact Patch
Michael McManus
B00525954
A Dissertation submitted in part fulfilments of the requirements
of the degree of;
Bachelor of Science with Honours in Civil Engineering
May 2014
2. 2
List of Tables.............................................................................................................. 3
List of Figures............................................................................................................. 4
List of Abbreviations................................................................................................... 6
Abstract...................................................................................................................... 7
Acknowledgements .................................................................................................... 8
1 Introduction........................................................................................................ 10
2 Literature Review............................................................................................... 14
3 Methodology...................................................................................................... 19
4 Thermal imaging of GripTester tyre during ULTRA testing................................ 31
5 3D Modelling...................................................................................................... 39
6 Analysis of Data................................................................................................. 44
7 Discussion ......................................................................................................... 60
8 Conclusions....................................................................................................... 63
9 Recommendations for further research ............................................................. 65
10 References..................................................................................................... 67
Appendix A............................................................................................................... 70
Appendix B............................................................................................................... 72
3. 3
List of Tables
Table 1 - Example of recorded tyre temperature during heating up period of the 65kph
with 30kg on high textured surface........................................................................... 70
Table 2 - Texture depth of new 14mm SMA............................................................. 71
Table 3 - Skid Resistance of 14mm SMA................................................................. 71
Table 4 - Example of data obtained from contact patch analysis with X3 software. 71
Table 5 - Tyre T2 under SOC................................................................................... 71
4. 4
List of Figures
Figure 1 - ROSANNE and how its predecessors link in............................................ 15
Figure 2 - ROSANNE Standardised trailer ............................................................... 16
Figure 3 - Modified Wheel Tracker........................................................................... 21
Figure 4 - Griptester Tyre with 4 points clearly marked ............................................ 22
Figure 5 - ULTRA Machine with curved specimens attached................................... 23
Figure 6 - Road Testing Machine ............................................................................. 23
Figure 7 - FLIR SC640 ............................................................................................. 24
Figure 8 - Both slabs that were created in the Laboratory........................................ 25
Figure 9 - Slab in Image Master 3D Model............................................................... 27
Figure 10 - Vinamould Peel...................................................................................... 27
Figure 11 - Steel Mould with Peel inserted............................................................... 28
Figure 12 - IR Camera viewing the wearing surface of the tyre as it runs on the ULTRA
Machine.................................................................................................................... 29
Figure 13 - Sidewall of tyre through Infra-red Camera ............................................. 32
Figure 14 - Line temperature across Wearing Surface of tyre.................................. 33
Figure 15 - Temperature Spots across wearing surface of tyre................................ 33
Figure 16 - Tyre temperature against elapsed time at 20kph with 50kg load ........... 34
Figure 17 - Spot temperatures in heating up period of 20kph with 50kg test (low
textured surface) ...................................................................................................... 34
Figure 18 - The Four chosen areas across the wearing surface for measuring
temperature.............................................................................................................. 35
Figure 19 - Tyre temperature across four areas during heat up period at 20kph with
50kg ......................................................................................................................... 36
Figure 20 - Tyre temperature over inner two areas during heat up period at20kph with
50kg ......................................................................................................................... 37
Figure 21 - Larger inner area incorporating both smaller inner areas from previous
tests.......................................................................................................................... 37
Figure 22 - Tyre temperature in large inner area during heating up period at 20kph
with 50kg.................................................................................................................. 38
Figure 23 - Plan view of Image Master 3D model through Mountains Map software 40
Figure 24 - Isometric view of 3D model shown in Mountains Map created with Image
Master Software ....................................................................................................... 40
Figure 25 - Isometric view of Image Master Model, focussed on area of slab from which
the ULTRA specimens were made........................................................................... 41
Figure 26 - Plan view of the area from which the ULTRA specimens were made. Model
created with Image Master, viewed in Mountains Map............................................. 42
Figure 27 - Plan view of Zephyr model through Mountains Map .............................. 42
Figure 28 - Isometric view of 3D Model created with Zephyr software. Model is viewed
in Mountains Map..................................................................................................... 43
Figure 29 - Tyre temperature in heating up period at 20kph on low textured surface
................................................................................................................................. 45
Figure 30 - Tyre temperature in the heating up period of the 50kph test on low textured
surface ..................................................................................................................... 45
Figure 31 - Tyre temperature in heating up period of the 65kph test on low textured
surface ..................................................................................................................... 46
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Figure 32 - Tyre temperature during heating up period at 20kph on high textured
surface ..................................................................................................................... 47
Figure 33 - Tyre temperature during heating up period at 50kph on high textured
surface ..................................................................................................................... 47
Figure 34 - Tyre temperature during heating up period at 65kph on high textured
surface ..................................................................................................................... 48
Figure 35 - Tyre temperature during heating up period of standard load and speed
(20kg and 20kph) ..................................................................................................... 49
Figure 36 - Tyre temperature after 300 seconds against load.................................. 50
Figure 37 - Contact Area of T2 with different inflation pressures.............................. 51
Figure 38 - Contact Area of T4 with different inflation pressures.............................. 51
Figure 39 - Average contact area of the T4 with varying load .................................. 52
Figure 40 - Average contact are of the T2 with varying load .................................... 52
Figure 41 - Average Contact patch area of T2 over four tyre locations .................... 53
Figure 42 - Average contact patch area of T4 over four tyre locations..................... 53
Figure 43 - Contact patch analysis on an under inflation tyre................................... 54
Figure 44 - Standard loaded tyre with standard inflation pressure ........................... 55
Figure 45 - Overinflated tyre with standard loading.................................................. 56
Figure 46 - Tyre contact area with standard inflation and no load............................ 57
Figure 47 - Tyre contact area with standard inflation and standard load.................. 58
Figure 48 - Contact patch of overloaded tyre with standard inflation pressure......... 59
Figure 49 - Thermal image of tyre showing the heat imprint of the road surface...... 61
6. 6
List of Abbreviations
ULTRA (Ulster Load Test Road Assimilator)
RTM (Road Test Machine)
SOC (Standard Operating Conditions)
SOP (Standard Operating Procedure)
SOL (Standard Operating Load)
IR (Infra-Red)
7. 7
Abstract
This project investigated the relationship between GripTester tyre temperature and
applied load. This was done using the ULTRA apparatus. The tests were carried out
using a cast taken from a 14mm Stone Mastic Asphalt slab prepared in the laboratory.
Fifteen curved test specimens were made from a Vinamould cast of the SMA. These
were fixed to the internal drum of the ULTRA to form a continuous textured surface.
The contact patch of the GripTester was measured using a modified wheel tracker and
XSensor pressure pad. The effect of tyre inflation pressure and applied static load was
determined. A FLIR SC640 thermal video camera was used to measure the change in
tyre temperature during ULTRA testing. The effect of speed, load and time was
assessed. 3D models of the asphalt slab texture were made using stereo
photogrammetry. The 3D models were created in Image Master and Zephyr. It was
found that the curved test specimens were a good representation of the SMA slab
texture. Increasing the load was found to increase the contact patch of the GripTester
tyre. Decreasing the inflation pressure was found to increase the patch area. It was
found that an increase in load, or an increase in speed increased the temperature of
the test tyre. After a period of time the temperature of the tyre reached an equilibrium
value in relation to the test conditions. It was observed that as the heated tyre came
to a stop the texture of the test specimens could be observed in the thermal images.
This suggests that this may be a new mechanism to explain the transfer of heat /
energy from the tyre to the road surface that is dependent on the road surface texture.
8. 8
Acknowledgements
I would like to thank my supervisor and lecturer Dr. Woodward, for the help and the
inspiration to pursue this topic. I would also like to thank PHD students Christopher
Tierney and Grainne McQuaid for their continual assistance and guidance throughout
this entire project; not forgetting laboratory technician Ian Martin for using his
knowledge and experience to help me with every completed test that was achieved
and my colleague Stephen Ellis who aided me with this project every step of the way.
I would like to thank Dr. Lyness for his early advice on planning and setting goals which
proved vital over the last few weeks.
Lastly I would like to thank my family and my girlfriend Aideen for tolerating my
workload in the more challenging times over this past year.
9. 9
Declaration
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11. 11
Introduction
As a tyre sits stationary on the pavement, it can be seen that its shape is almost
entirely round, except for the part that touches the pavement. This is the contact patch.
It is forced into this shape because of the load of the car acting downward upon it and
with rubber being a flexible material, it bends accordingly.
As a car begins to move, the tyre turns, and the part of the tyre that was flat when it
was stationary, springs back into its regular circular shape, while the next part of the
tyre bends into the flat position. This is happening the tyre continually as it rolls so that
the whole of the tyre will have been bent out of shape and sprang back to its normal
position. This movement causes tiny heat increases throughout the tyre which can
build up over time.
When the load is increased on the tyre, the part of the tyre that touches the road and
becomes flat increases. This means that there is more flexing movement within the
tyre and temperature will increase faster and to a higher level. It is important to study
the temperature of the tyre as a hotter tyre provides better grip qualities, which means
better traction and turning qualities. Given this it would then go some way to
developing an understanding of whether increasing load on a tyre produces better skid
resistance and better turning functionality for the driver for commercial and safety
purposes.
1.1 Review of Relevant literature
Although there is a vast library of literature available in this area, the most relevant is
the literature would be the most recently written. This is because there has been
extensive investigation in the area, and this research will be built upon with more
research by numerous authors, because of this it is quite easy to duplicate work. It is
important to have an appreciation for what work has come before this project and what
the current thinking is in order to draw conclusions and reaffirm others.
1.2 Create suitable surfaces, make vinamould cast, prepare ULTRA test
specimens
The required software and machines are all provided in the Highways lab in the
University of Ulster, Jordanstown; but the materials required to be obtained from
outside are aggregates for the creation of the asphalt sample surface, aggregates for
the creation of the ULTRA test specimen, which is concrete based and will need a
bonding agent; a bituminous substance will be needed to bond the aggregates of the
asphalt sample surface; and the solid vinamould required for making the peel which
will face the ULTRA test specimens.
1.3 Carry out ULTRA testing and look at the effects of tyre inflation, applied load
and drum speed on tyre temperature
To become familiar with the ULTRA machine, tests were first of all ran using pre-
existing ULTRA test specimens according to BS AU 50-1.1.3:1993, this gave baseline
data on how the tyre performed which could then be referred to when the results of
the main tests were obtained. During this time it was be decided what the best ways
were to complete the experiments and work out the nuances that may have occurred
12. 12
with any type of experiment. This way it meant that the main part of the experiment
ran smoothly.
1.4 Analyse data to find relationships between factors (temperature/ inflation/ tyre
wear)
To analyse the data it must first be gathered accurately. The temperatures of the tyre
were recorded using a thermographic camera, the data was collected on a
spreadsheet and then scatter charts were prepared. Commentary on the graphs then
began and then a comparative analysis between experimental conditions and
performance. It was then possible to define a relationship between the variables and
the results.
1.5 Make recommendations to use of friction measuring tyre (ASTM 10x 4-5)
After the analysing the findings of this project, there were informed recommendations
made as to what should be studied next in relation to this type of tyre, calling on all
knowledge and findings discovered during this project / dissertation.
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2 Literature Review
2.1 Introduction
This following literature review considers the most current and relevant literature in
this area. The measurement of tyre properties is very topical at the moment. This
project is more based on measuring tyre properties under certain conditions, which
can be very topical also. It is important that new understanding of this issue is gained
through experimentation as it fundamentally relates back to road safety. It is an area
that is receiving increasing levels of interest and research.
2.2 Review of Relevant Literature
Load in relation to this project refers to the direct loading on the tyre as it performs,
this will be the main area of interest. It is hoped that the results produced will enable
some level of relationship between load and other factors. When referring to tyre
temperature, this is the observation of the build-up or generation of heat of the tyre
under certain conditions. A heated tyre will perform differently than one that has a
normal temperature. The tyre heats up when working due to the hysteretic friction upon
it. The contact patch is the area of the tyre that is in contact with the asphalt. The study
of this area is to observe how pressure is distributed and how the tyre’s contact patch
wears over time with the friction it is subject to when being used on the road.
Load affecting tyre temperature and contact patch is the basis of this project.
According to Tang (2013) loading is the central dynamic in ascertaining the
temperature range. The purpose of that project was to develop a finite element
approach to computationally evaluate the temperature field of a steady-state rolling
tyre. It proves somewhat similar to this project in parts. Furthermore it affirms that
increasing normal load increases elastic deformation which increases the total strain
energy density and ultimately temperature. There can be great variation of
temperatures recorded when measuring friction of a tyre.
The general view is that with increasing the load, the temperature of the tyre will also
increase. This is what the results in Influence of temperature of Tire-Pavement friction
(Srirangam, 2013) would also attest to – “Hysteretic friction of the tyre rubber
decreases with increase in temperature”. In the Srirangam’s project, a thermo-
mechanical coupling model was acquired using laboratory test data to calculate the
developmental progress of the effect temperature has on the hysteretic friction.
Tang (2013) has further positions on temperature, having identified that increasing
load increases the temperature, and it would appear that elastic deformation is another
key factor in this study also. An increase in inflation pressure decreases temperature
in the tyre due to a decrease in elastic deformation; identifying tyre inflation pressure
as another key factor. Although the study does then go on to show that temperature
distribution is principally determined by the load and then inflation pressure. The study
also demonstrates that the building up of heat due to hysteretic friction in the tyre is
decreased with an increase of body-ply stiffness. Body-ply stiffness will not be varied
in this project as the GripTester tyre will be used for all samples, though it is interesting
to see this relationship.
Cho (2013) also shows a relationship involving heat in a tyre, as that project shows a
great increase in temperature with the velocity it has been moving at. A small and slow
15. 15
decrease is also shown from hysteretic loss and rolling resistance when the velocity
was increased. The speed of the Ulster Load Tyre Road Assimilator (ULTRA machine)
will be another influence that will be examined during this project, with a similar
relationship expected to be shown.
To further examine the samples and tyre, the temperature in the room could be varied,
to see what reaction this will have on them. Increase of ambient temperature should
cause the tyre temperature to rise. The increase of ambient temperature on in the
environment in which the tyre is being tested would have a large effect on tyre
deformation (Y. Li, 2012).
An interesting area of this is tyre inflation pressure. This can be varied to study the
different results and effect that it has on areas such as the contact patch, tyre
temperature and wear. Different result relationships can be discovered depending on
the specifics of the samples and the type of test. For example, on a wet grip
measurement (Woodward, 2013) a new tyre was rather unaffected by inflation
pressure. However on a tyre when the rolling resistance was measured of a radial
play tyre (Taghavifar, 2013) an increase in inflation pressure produced a decrease in
rolling resistance, particularly at higher values of vertical load.
As Tang (2013) affirmed that inflation pressure was a secondary factor in determining
temperature distribution in a tyre, it may prove to be more prominent in other studies.
The contact area is the part of the tyre that is in contact with the asphalt and can be
affected by load or tyre inflation pressure. It was found that increasing the contact area
decreases the wet grip in a GripTester tyre which was an unexpected relationship
(Woodward, 2013). There is also a linear relationship shown between contact width
and inflation pressure. The differences were quite small and a normal working
pressure, but at the extremes there were variations, particularly at lower inflation
pressures.
A displacement pattern is shown to be proportionate to the time and space varying
contact pressure in Tyre-road contact using a particle-envelope surface model
(Pinnington, 2013). This was a proposed procedure to find the contact forces under a
rolling tyre.
Currently there is a similar project to this one in the Austrian Institute of Technology
called ROSANNE or Rolling resistance, skid resistance, and noise emission
measurement standards for road surfaces.
“The main objective of this project is to advance the harmonization of measurement
methods for skid resistance, noise emission and rolling resistance of road pavements
and prepare for standardization.
In this the project will follow the recommendations of key predecessor projects like
TYROSAFE, HERMES, SILVIA and MIRIAM.
16. 16
Figure 2 - ROSANNE Standardised trailer
Figure 1 – How ROSANNE and its predecessors link together
The project aims at performing prenormative research to enable the creation or
improvement of European standards in the working field of the working group CEN TC
227 / WG5.” (Spielhofer, 2013)
For measuring rolling resistance the operatives intend to standardize trailer
measurements, study influencing road surface parameters, develop correction
procedures for influences, investigate link to vehicle fuel consumption.
A key predecessor of the ROSANNE project mentioned here was Tyre and Road
Surface Optimisation for Skid Resistance and Further Effects (TYROSAFE) which also
17. 17
measured rolling resistance, it did not only focus on the road surface but also on tyres
and on the interaction between the road surface and tyres. This project provided a
synopsis of the current state of scientific understanding and its current application in
national and European standards. It identified the needs for future research and
proposes a way forward in the context of the future objectives of European road
administrations in order to optimise three key properties of European roads: skid
resistance, rolling resistance and tyre/road noise emission.
The TYROSAFE contribution in all these three areas will help the public authorities of
the Member States to use existing and new research knowledge to reduce fatalities
and promote environmental compatibility of road surfaces. In addition, the project
created a solid scientific background for further research and for the development of
harmonised policies with regard to essential road surface properties.
There were 6 WP (Work Packages) involved with this project:
WP1: Policies of EU countries for skid resistance / rolling resistance / noise
emissions
WP2: Harmonisation of skid-resistance test methods and choice of reference
surfaces
WP3: Road surfaces properties – skid resistance / rolling resistance / noise
emissions
WP4: Environmental effects and impact of climatic change – skid resistance /
rolling resistance / noise emissions
WP5: Dissemination and raising awareness
WP6: Management
Methods used to examine the rolling resistance of road pavements were:
• Measurements using a drum (in some cases real surfaces applied)
• Measurements using a special trailer on real surfaces.
• Measurements using vehicles that are equipped with a device to measure the fuel
consumption.
In addition to these basic principles, a study at the Transport Research Laboratory in
the UK has used a facility designed to assess the strength of road pavements to
attempt to measure rolling resistance on truck tyres. This large facility uses a loaded
truck tyre that is moved repeatedly from side to side across specially constructed
pavements. The one aspect of the study was to measure rolling resistance on
pavements constructed with different strengths and textures.
This is particular area of TYROSAFE is very relevant to this project as this is similar
to what the intent is to study here also. In comparison with TYROSAFE this study is
completely lab based, where the alternative is using a standardized trailer and finding
an area of the road to test as seen here.
“Rolling resistance is a physical phenomenon that results in energy loss while moving
a wheel or tyre over a surface. Hans Bendtsen from the Danish Road Institute (DRI)
[5] identifies
18. 18
Three main mechanisms through which the energy is lost:
1. Losses due to the bending/deformation of the tyre sidewalls.
2. Losses due to micro-deformation of the tyre tread in the contact area.
3. Losses due to slippage friction in the contact area between the tyre and the surface.”
(Nitsche, Spielhofer 2009)
In summary the relationships shown in recent and relative literature are:
• Load increases elastic deformation which increases the total strain energy
density and ultimately temperature.
• Hysteretic friction of the tire rubber decreases with increase in temperature.
• Increase in inflation pressure decreases temperature in the tyre.
• Temperature distribution is principally determined by the load.
• There is a great increase in tyre temperature with the velocity.
• Increase of ambient temperature has a large effect on tyre deformation and
cause the tyre temperature to rise.
It was suggested that the development of contact area and pressure distribution is
possible using pressure map systems and that further work is required to determine
the effect of pressure distribution within the contact area (Friel 2013), (Woodward,
2013).
2.3 Critical Literature Review
From what has been found in the recent relevant literature it is clear that there are still
gaps in knowledge with regard to heat and energy loss from tyres as they are in use,
and also how this may affect rolling resistance, skid resistance and noise emissions.
This project will attempt to fill in at least some of these areas with testing and analysis
of tyre temperature under load.
20. 20
3.1 Detailed Methodology
This is the detailed process in which this project was carried out, including research
actual experimentation, and the analysis of the results. The following summarises the
main methodology.
• Make 14mm Stone Mastic Asphalt (SMA14) slab sample for preparation of
curved test specimens and for 3D modelling.
• Make 3D model of 14mm SMA
• Make Vinamould peel of new 14mm SMA slab
• Make 15 curved test specimens of high textured SMA14.
• Assess contact patch for new GripTester tyre T4 using an XSensor pressure
pad.
• Carryout ULTRA testing on low textured micro-asphalt test specimens using
T4 tyre.
• Assess contact patch for GripTester tyre T4 using an XSensor pressure pad
after ULTRA testing of low textured micro-asphalt test specimens.
• Assess contact patch for new GripTester tyre T2 using an XSensor pressure
pad.
• Carryout ULTRA testing on SMA14 test specimens using T2 tyre.
• Assess contact patch for GripTester tyre T2 using an XSensor pressure pad
after ULTRA testing of SMA14.
• Analysis of data.
3.2 Experimental Apparatus
The experimental programme involved the use of the following equipment: ULTRA
apparatus, FLIR thermal video camera, XSensor pressure pad, and modified wheel
track apparatus.
Modified Wheel Tracker
The wheel tracker (Figure 3) is a machine that allows the wheel to be placed on a
surface and ran at a certain speed, it also allows weights to be applied to it for
manipulated the performance of the wheel.
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Figure 3 - Modified Wheel Tracker
XSensor Pressure Pad
The Pressure pad is a technical piece of equipment which can map out pressure being
applied to it onto a computer, for in-depth analysis of the intricacies of the points of
pressure being imposed. It can be placed under the GripTester tyre on the wheel
tracker to give a representation of the pressure the tyre is under when the different
conditions are placed on it, be they varying load or inflation pressure, these tests were
carried out during the process of the ULTRA testing to ensure that the tyre’s contact
patch could be analysed from different points in its life cycle.
GripTester Tyre
The GripTester Tyre (Figure 4) is the standard tyre used for friction measurement
according to BS 7941-2:2000, it has a smooth surface from when it is brand new so
has no texture/treads and this actually makes it very useful when testing as it gives a
worst case scenario in terms of skid resistance during wet testing, as there are no
treads to displace the water out the side of the tyre which counteracts aquaplaning.
The tyre has four areas marked for contact patch analysis.
22. 22
Figure 4 - Griptester Tyre with 4 points clearly marked
ULTRA Machine
The ULTRA machine (Figure 5) is unique to the University of Ulster and it is essentially
a large rotating drum at which the speed can vary. A tyre can be placed inside it to
measure samples and weights can be applied to the tyre to increase the load. The
construction of the ULTRA machine means that variables such as surface texture,
speed and load may be examined, utilising different tyres permits comparable analysis
of the system behaviour. Varying the load and speed helped to understand the
different reactions of a tyre under these conditions, and to see if certain relationships
only exist under certain conditions or not.
23. 23
Figure 5 - ULTRA Machine with curved specimens attached
Road Testing Machine
The Road Testing machine is available in the highways lab of Jordanstown campus of
the University of Ulster. It rotates in a circle and has tyres that move over every part
of a sample. In this case the slabs that were made were tested on this for 2000 passes
simulating the normal wearing process on a newly laid highway surface. This was to
run off any excessive bitumen that is likely to be on the slab for the purpose of the
vinamould peel.
Figure 6 - Road Testing Machine
24. 24
FLIR Camera
The camera that was used to monitor the ULTRA testing is the FLIR SC640. This
camera specifies in monitoring temperatures between -40° to +1500°C. This gives a
very good range of temperatures that can be accurately measured with an error
allowance of ±1°C or ±1% of the reading.
Figure 7 - FLIR SC640
3.3 Experimental Procedure
3.3.1 Make 14mm Stone Mastic Asphalt (SMA14) slab sample for preparation of
curved test specimens and for 3D modelling.
Attaining aggregates is the first thing that was done before making slabs of Stone
Mastic Asphalt (SMA). They were obtained from an aggregate company. These were
made with the purpose of moulding samples on this particular slab.
The new slabs then ran on the Road Test Machine for two hours/2000 passes to run
off any excessive bitumen on the top of the surface for the purpose of creating a good
representative mould of 14mm road surface and so that the vinamould peel did not
take off any bitumen in the process of the peel.
The slabs that were made are shown in Figure 8, for the purpose of making a peel,
the best representation of a high quality 14mm asphalt was to be chosen. The slab on
the left was chosen as its texture is clearly viewable and there is still excess bitumen
on the slab on the right.
25. 25
Figure 8 - Both slabs that were created in the Laboratory
3.3.2 Make 3D model of 14mm SMA
The following are the steps taken to create a 3D model in Image Master.
To create a 3D drawing in Image Master, first:
Click New Project
Name the project
Click OK
Click into Orientation
Load Points File
Select the control points file.
OK
Import
These will then load.
OK
Click Register Image (Camera Icon)
Look in the file with the images
Select
Camera name – Load the calibration file
Select all
Register
26. 26
Do not copy the images into Model folder.
Select the two pictures need in order which is actually left to right.
Orientation
Add Stereo Pair
Move to Stereo List
Double click image of slab.
Click Measure Tie Point
Name the first point 1
Select control point 1 on both drawings, trying to get them as accurately in the middle
as possible. Repeat for all control points.
Click Calculate
Calculate co-ordinates
Select all
Register Co-ordinates
Save
Save as mathematical system
Camera locations
Select all
Register
Save
Mathematical
Close
Go to Model Space
Draw polyline around the control points
Select the polyline
Auto Surface Measurement
New Layer
OK
Mesh interval 0.5mm
Turn off all filters.
OK
27. 27
Figure 9 - Slab in Image Master 3D Model
Figure 10 - Vinamould Peel
After some working time this will bring up the 3D Projection of the Slab (Figure 9).
3.3.3 Make Vinamould peel of new 14mm SMA slab
The samples were made of concrete and were required to have the same texture as
the slab. This was achieved by making a vinamould model of the top of the specimen.
Hot liquid vinamould was poured over the slab and allowed to solidify. It was then be
peeled off and an area was used to deliver mould samples representative of the
texture. This is called the vinamould peel (Figure 10).
28. 28
Figure 11 - Steel Mould with Peel inserted
3.3.4 Make 15 curved test specimens of high textured SMA14.
Once the wet concrete samples were in the mould the vinamould cast was placed on
top of them and let set in this mould. Once settled the vinamould was peeled off again
and used for the next sample and so forth. Approximately two samples could be made
in a day, so eight days in the lab were required to make the fifteen required (with a
spare for control purposes and in case of failure). The resin used in the moulds will be
Nitromortar PE Catalyst Filler which will be obtained from Fosroc in Mallusk, Co.
Antrim.
3.3.5 Assess contact patch for new GripTester tyre T4 using an XSensor pressure
pad.
To create a new pressure mat reference first:
Click File
New
OK
Press F8 on the keyboard.
29. 29
Figure 12 - IR Camera viewing the wearing surface of the tyre as it runs on the
ULTRA Machine
This will then make the software take 100 images of the applied pressure
representation in that area. To create an image and get data that incorporates all of
the 100 images.
Click Tools
Merge
OK.
The contact area will be displayed on a table on the right hand side of the screen in
mm².
3.3.6 Carryout ULTRA testing on low textured micro-asphalt test specimens using T4
tyre.
On the ULTRA machine the samples were all placed on rotating cylinder facing
inwards. The GripTester wheel was in place to run on the samples as the cylinder
rotated. Various speeds can be achieved with this machine, and on the fitting for the
wheel, there is the capability of adding weight with weighted plates, so a good variation
was reached here. The tyre and samples were shot with a thermographic camera; this
showed the heat in detail across the tyre and the specimens. Expectantly there was a
relationship interpreted between load and temperature, and between velocity and
temperature with the findings of the camera.
The low textured samples were a Gripfibre Microasphalt. The test was run at speeds
of 20kph, 50kph and 65kph. During which time there was a thermographic camera
filming the wearing surface of the tyre. At each speed, two overloading conditions were
tested, 31kg and 46kg. The load went right down the axel.
30. 30
3.3.7 Assess contact patch for GripTester tyre T4 using an XSensor pressure pad
after ULTRA testing of low textured micro-asphalt test specimens.
The contact patch was analysed in the same way as the previous test to give
comparable results.
3.3.8 Assess contact patch for new GripTester tyre T2 using an XSensor pressure
pad.
See above.
3.3.9 Carryout ULTRA testing on SMA14 test specimens using T2 tyre.
The high textured samples were a Stone Mastic Asphalt (SMA). The test was run at
the same conditions as the low textured samples to give comparable data.
3.3.10 Assess contact patch for GripTester tyre T2 using an XSensor pressure pad
after ULTRA testing of SMA14.
See above.
3.3.11 Analysis of data.
The data was graphed and each test was compared to show the differences of the
temperature that was achieved under the different conditions of testing. The contact
area of the tyres under the different loads and inflation pressures were graphed and
compared.
3.3.12 Software Analysis
The different software used for making the 3D models, Image Master and Zephyr will
be analysed comparing ease of use, accuracy and speed.
Image Master is a software that has been used in the University successfully. It
requires the slab to be photographed in a control from with known heights and control
points and the points have to be accurately clicked in the centre on two images of the
slab.
The Zephyr software similarly models the slab from images but does not require a
control frame. Although a control frame can be used, it is easier to just take the photos
normally, as it does not require that the whole sample must be in the picture. The
software can recognise similarities in the pictures and map out the photos itself.
3.3.13 Health and Safety in the Laboratory
A risk assessment was completed and presented to the supervisor/advisor (Dr.
Woodward) for approval and a copy of this risk assessment kept in the laboratory at
all times. A copy of the risk assessment is shown in Appendix B.
32. 32
Figure 13 - Sidewall of tyre through Infra-red Camera
4.1 Introduction
This chapter considers thermal imaging of the GripTester tyre during ULTRA testing.
This was quite difficult and involved the following stages:
• Initial attempts – Measurement of the tyre sidewall temperature
This (Figure 13) is the first area on the tyre at which the Infra-red camera was aimed
at. Little if any heating up can be seen at the side. It was decided that the wearing
surface would be a better area to focus one, as the tyre heats up a lot more across its
contact patch.
• Measurement of the wearing surface of the tyre
As the temperature of the tyre was then measured, there was an option to draw a
straight line across the face of the wearing surface. This allowed a temperature of the
whole surface to be taken, this could not have given a good representation of the heat
up the tyre’s wearing surface as there was obviously great variation in the temperature
at different parts of the tyre. It was then decided that there should be a series of spot
temperatures taken across a line on the wearing surface.
33. 33
Figure 14 - Line temperature across Wearing Surface of tyre
Figure 15 - Temperature Spots across wearing surface of tyre
34. 34
15.0
20.0
25.0
30.0
35.0
40.0
45.0
0 1000 2000 3000 4000 5000 6000
Temperature,°C
Elapsed time, seconds
Sp2
SP3
SP4
SP5
SP6
SP7
SP8
SP9
SP10
SP11
SP12
SP13
SP14
Figure 16 - Tyre temperature against elapsed time at 20kph with 50kg load
15.0
20.0
25.0
30.0
35.0
40.0
45.0
0 200 400 600 800 1000
Temperature°C
Elapsed Seconds
Sp2
SP3
SP4
SP5
SP6
SP7
SP8
SP9
SP10
SP11
SP12
SP13
SP14
Figure 17 - Spot temperatures in heating up period of 20kph with 50kg test (low
textured surface)
This (Figure 16) is the temperature of the tyre over for the duration of the first test and
the period that it took to cool down. It can be seen that the tyre was measured 17
points across the wearing surface. It can also be seen that the temperature of the tyre
very much stabilises after it reaches its initial highest temperature after approximately
1000 seconds. For the purpose of graphing the data a graph with just the heat up
process would be more appropriate.
35. 35
Figure 18 - The Four chosen areas across the wearing surface for measuring
temperature
This (Figure 17) is a better representation of how the load affects what temperature
the tyre gets to, it clearly shows the first 1000 seconds, and this allows further
examination of the period in question.
It can be seen that the tyre is much hotter on the outer edges than in the centre. This
is believed to be because, due to the loading, the outer areas are subject to flexure as
they are being pushed down more than the centre which is already lower; and the heat
comes from when the tyre stretches and releases its energy.
As there is a great variation in the spot temperatures depending on the area on the
tyre, it is better to split the temperature profile into representative areas across the
wearing surface.
Figure 18 identifies the areas that were chosen. It can be seen that the two outer areas
are hotter than the inner ones on the graph which shows the areas’ temperatures over
the heating up period. The inner areas were identified as the most representative of
the temperature achieved by the wearing surface of the tyre. Thus an average of the
temperatures taken from these areas was used to deliver an overall tyre temperature
for comparative analysis.
Here (Figure 19) is a graph showing the temperature of the areas as they were heated
up during the process of the test. It can be seen that once again there is some variation
depending on the area of the proximity to the sidewalls.
36. 36
Figure 19 - Tyre temperature across four areas during heat up period at 20kph with
50kg
The inner areas of the tyre fit in a lot more with the majority of the tyre’s points on a
temperature scale and therefore it is better to just use the two inners areas for a
representation of the tyre temperature.
15
17
19
21
23
25
27
29
31
33
35
0 200 400 600 800 1000
Temperature°C
Elapsed Seconds
Area 1
Area 2
Area 3
Area 4
37. 37
15
17
19
21
23
25
27
29
31
33
35
0 200 400 600 800 1000
Temperature°C
Elapsed Seconds
Area 2
Area 3
Figure 20 - Tyre temperature over inner two areas during heat up period at20kph with
50kg
Figure 21 - Larger inner area incorporating both smaller inner areas from
previous tests
This is better representation of the temperature of the tyre during the heating up
process under load but still shows some variation. A larger area covering both areas
2 and 3 may actually prove to be a better solution for measuring the typical
temperature of the tyre, shown in Figure 21.
40. 40
Figure 23 - Plan view of Image Master 3D model through Mountains
Map software
Figure 24 - Isometric view of 3D model shown in Mountains Map
created with Image Master Software
5.1 Image Master
This (Figure 23) is the Topcon Image Master model of the road surface that was made
in the lab after it has been processed through the Mountains Map software for analysis.
It is quite accurate and the slab’s texture depth can be seen in all of its areas. The
elastic bands which were used to hold the slab in place for photographing can be seen
as red anomalies in the top corners.
41. 41
Figure 25 - Isometric view of Image Master Model, focussed on area of slab from
which the ULTRA specimens were made
Figure 24 is an isometric view of the 3D model of the slab which shows the entire slab
as it might appear on the road, the different colours indicate the texture depth of the
slab and it can be seen that the outer areas are a brighter red indicating above 22mm
and the inner areas are a mixture of more blue and green colours which indicates
above 15mm and below 22mm.
Figure 25 is the area of the slab from which the vinamould peel was cut for the creation
of ULTRA test specimen. A significant range in porosity can be seen from a higher
texture depth on the upper left side to a lower texture depth on the lower right side.
42. 42
Figure 26 - Plan view of the area from which the ULTRA specimens were
made. Model created with Image Master, viewed in Mountains Map.
Figure 26 is a plan view of the 3D model of the area of the slab which was used for
ULTRA test specimen. The red areas indicate where the aggregate was and the
blue/green areas are where there is macro texture.
5.2 Zephyr
Figure 27 - Plan view of Zephyr model through Mountains Map
Shown in Figure 27 is a plan view of the area of the slab which was used for ULTRA
test specimen, it is taken from the 3D model of this which was made using the new
Zephyr software. This is one of the first times the software was used. The red areas
indicate where the aggregate is and the blue areas indicate the macro texture.
Unfortunately the model is not well scaled due what must have been an oversight in
the using of the software.
43. 43
Figure 28 - Isometric view of 3D Model created with Zephyr
software. Model is viewed in Mountains Map
This is an isometric view of the sample area for which the ULTRA test specimen was
modelled on. Down the sides of the aggregates there is some visible rippling, this is
possibly due to the fact that no isometric pictures were used for the modelling, although
there were 96 plan view photos used across this small 200mm × 125mm area to
ensure that the model would be high quality.
One of the best features of Zephyr is that control points do not need to be included
and that the software can recognise similarities in each picture and map out the
pictures in relation to how the model should look itself. This feature was taken
advantage of in the creation of this model, as the 96 consecutive pictures taken were
very close to the actual slab, meaning that it would be impossible to get the whole slab
into the picture but that the content of each photo was very detailed. It was thought
that this would give very good quality. The addition of some isometric view photos
would have given better quality, and also the addition of a scale, which would have
enabled some greater analysis for the purpose of this report.
The model that was made in Image Master is a better quality one, though it took much
longer to make and the control points process is tedious in comparison to the ease of
creating the drawing with Zephyr which virtually only needs three functions. With the
introduction of the extra camera angles for the Zephyr model and scaling, a better
representation of Zephyrs true potential could be realised.
45. 45
Figure 29 - Tyre temperature in heating up period at 20kph on low textured surface
18
22
26
30
34
38
42
0 100 200 300 400 500 600 700 800 900 1000
Temperature°
Elapsed Seconds
20kg
30kg
50kg
18
22
26
30
34
38
42
46
0 100 200 300 400 500 600 700 800 900 1000
Temperature°C
Elapsed Seconds
20kg
30kg
50kg
Figure 30 - Tyre temperature in the heating up period of the 50kph test on low
textured surface
6.1 Tyre Temperature
6.1.1 Low Textured Surface
Figure 29 shows the test at one of the lowest testing speeds specified in BS 7941-
2:2000, i.e. 20kph. The graph included the Standard Operating Load (SOL) of 20kg,
30kg and 50kg experimental results. It can be seen that the Standard operating load
reached the lowest temperature around 28°C with the two overloaded tests
significantly higher. The load was 30kg which has produced an intermediate
temperature of around 30°. The 50kg loaded tyre produced a temperature of around
32°C.
46. 46
18
22
26
30
34
38
42
0 100 200 300 400 500 600 700 800 900 1000
Temperature°C
Elapsed Seconds
20kg
30kg
50kg
Figure 31 - Tyre temperature in heating up period of the 65kph test on low textured
surface
This (Figure 30) is the test at 50kph on the old surface. There seems to be a lot of
variation on the Standard Operating Load test, which could be due to the wheel
bouncing on the surface, meaning that the distance between the camera and the tyre
changes slightly throughout the test, the significance of this only became apparent due
to the close observation of the tyre at close to the minimum operating range of the
camera. The load applied to the other test may have damped the vibration and
therefore there is a lot less oscillation on those results. The tyre heats up to above
30°and below 34°C with the Standard Operating Load. The 30kg test levels off around
the 36°C and the 50kg is higher, peaking at approximately 40°C.
Figure 31 is the old surface test at 65kph. The SOL test levels off below the 36°C
mark. The 30kg test levels off at a higher temperature of below 40°. The 50kg test
reaches just below 44° before it begins to level off.
47. 47
18.0
22.0
26.0
30.0
34.0
38.0
0 100 200 300 400 500 600 700 800 900 1000
Temperature°
Elapsed Seconds
20kg
30kg
50kg
Figure 32 - Tyre temperature during heating up period at 20kph on high textured
surface
18.0
22.0
26.0
30.0
34.0
38.0
0 100 200 300 400 500 600 700 800 900 1000
Temperature°C
Elapsed seconds
20kg
30kg
50kg
Figure 33 - Tyre temperature during heating up period at 50kph on high textured
surface
6.1.2 High textured surface
Shown in Figure 32 at 20kph the temperature of the tyre started at 22°C. The standard
loaded tyre initially heated up quicker than the overloaded tests but levelled off after
around 300 seconds, at which stage the loaded tyres were still steadily increasing in
temperature. Both loaded tyres ended up around the 30°C mark with the heavier
loaded test producing the slightly hotter temperature.
48. 48
18.0
22.0
26.0
30.0
34.0
38.0
0 100 200 300 400 500 600 700 800 900 1000
Temperature°C
Elapsed Seconds
20kg
30kg
50kg
Figure 34 - Tyre temperature during heating up period at 65kph on high textured
surface
Shown on Figure 33 at 50kph the temperature again started at around the 22° mark.
The temperature rises quickly on all tests, with the standard loaded tyre levelling off at
around the 32° mark and the overloaded tyres rising to higher temperatures and rising
more rapidly also. Both overloaded tyres rise to around 36° with the heaviest loaded
tyre slightly higher in temperature than the other.
At 65kph Figure 34 shows the temperature of the Standard loaded tyre and the
heaviest loaded tyre started off virtually the same at around 24° and the 30kg loaded
tyre started lower at around 20°. The increase in temperature is rapid on all tests but
the standard loaded tyre’s temperature levels off shortly after 200 seconds at around
33°. The overloaded tyres’ temperatures continue to rise with the 30kg loaded tyre
reaching around 36° and the heaviest tyre at almost 40°. The overloaded tyres level
off at virtually the same time.
6.1.3 Observations
From the graphs shown, it can be observed that on the low textured surface at 20kph,
the expected relationship between load and tyre temperature is found.
The 50kph and the 65kph tests on the same surface show very similar patterns of how
the tyre heats up under the different loads. The heavier loaded tyres show higher
temperatures than those that are not as heavily loaded.
On the new surface, on the 20kph test, the tyre temperatures are very similar, showing
small variation but the more heavily loaded the tyre is the higher the temperature is.
Increasing the speed produced much higher temperatures on the tyre for the 50kph
test and a small bit higher than that for the 65kph test. All tests on the new surface
showed the predicted relationship between increasing load and temperature.
49. 49
15
17
19
21
23
25
27
29
31
33
35
0 200 400 600 800 1000
Temperature°
Elapsed Seconds
High Texture
Low Texture
Figure 35 - Tyre temperature during heating up period of standard load and speed
(20kg and 20kph)
6.1.4 Comparisons
By comparison the first surface shows a lot less variation than the second. This could
be due to the fact that the first surface was quite worn, and therefore having less of an
effect on the tyre when the speed is increased. The second surface shows a lot more
variation and the immediate aspect that is noticed is that when the speed is increased,
the tyre temperature increases also. The predicted relationship between load and tyre
temperature is shown also, as the load on the tyre increases the temperature of the
tyre increases also.
The first surface shows a lot more variation in the temperature of single tests. This
may be due to the fact that it is so worn that it is not as smooth to drive on as the new
14mm asphalt, making the wheel bounce around and therefore changing distance
between the tyre and the camera, possibly causing it to be out of focus and
misreporting temperatures from areas a little closer to the undesired outside areas of
the tyre which are much hotter due to the deformation that they are experiencing with
the load.
Figure 35 shows the Tyre temperature as it heated up on the Standard Operating
Conditions over both surfaces, low textured and high textured. It can be seen that the
low textured surface pushed the temperature up a lot higher than the high textured
surface. It can also be seen that the rate at which the temperature rises over the first
200 seconds is much sharper.
50. 50
25
27
29
31
33
35
37
39
41
20 30 40 50
Temperature°C
Load kg
Low texture 20kph
Low texture 50kph
Low texture 65kph
High texture 20kph
High texture 50kph
High texture 65kph
Figure 36 - Tyre temperature after 300 seconds against load
From the previous tyre heating up period graphs, it can be seen that the temperature
of the temperature levels off and reaches equilibrium much sooner than 1000 seconds.
In fact around 300 seconds it appears to have been the most common time from which
the temperature level flattens. Figure 36 shows a graph which compares the
temperatures of all the tests after 300 seconds. There is great variation, especially in
the low textured surface. The high textured surfaces shows variation but in a more
phased way. The relationship is clear from both surfaces that the higher the speed,
the higher the temperature will increase.
51. 51
800
1000
1200
1400
1600
1800
2000
2200
8 13 18 23 28 33
AverageAreamm²
Inflation (PSI)
Figure 37 - Contact Area of T2 with different inflation pressures
800
1000
1200
1400
1600
1800
2000
2200
8 13 18 23 28 33
ContactAreamm²
Inflation (PSI)
Figure 38 - Contact Area of T4 with different inflation pressures
6.2 Contact Patch
6.2.1 Inflation
As shown on Figure 37, the tyre was overinflated to 30psi. The average contact area
decreased slightly below the average contact under the standard inflation; which was
close to 1250mm². The tyre was then deflated to 15psi, and the average contact area
increased above 1500mm². Further deflation of the tyre to 10psi resulted in an average
contact area even larger at approximately 2000mm².
52. 52
800
1000
1200
1400
1600
1800
2000
2200
0 1 2 3 4 5 6
ContactAreamm²
Load kg
Figure 39 - Average contact area of the T4 with varying load
800
1000
1200
1400
1600
1800
2000
2200
0 1 2 3 4 5 6
ContactAreamm²
Load kg
Figure 40 - Average contact are of the T2 with varying load
Figure 38 shows the variation in Contact patch area. At the lowest inflation, the contact
area is at its highest at under 1800mm². At the next higher inflation level 15psi, the
contact area is lower at just under 1600mm². At the standard inflation 20psi, the
contact area was over 1000mm². The overinflated tyre at 30psi had a contact area of
just under 1200mm² but was still higher than expected, showing an increase from
standard inflation.
6.2.2 Load
This is the average contact area of the T4. Decreasing from the SOL (3.3kg) brings
the average contact area down to 1000mm². The SOL produces a contact area of
approximately 1100mm². While increasing the load up to 4.3kg brings the contact area
to 1400mm².
53. 53
1000 1100 1200 1300 1400 1500
New T2
Worn T2
Contact area mm²
4
3
2
1
Figure 41 - Average Contact patch area of T2 over four tyre locations
0 500 1000 1500
New T4
Worn T4
Contact area mm²
4
3
2
1
Figure 42 - Average contact patch area of T4 over four tyre locations
As shown, the standard load (3.3kg) produces an average contact area of about
1200mm². Moving lower than the standard load, by removing the 3.3kg load, the
average contact area drops to around 800mm². Adding an extra kg to the standard
load brings it up to 4.3kg and the average contact area increases to around 1400mm².
Adding another 1.5kg to this brings the load up to 5.8kg and the average contact area
increases approximately another 200mm² to about 1600mm².
6.2.3 Comparisons
The average contact patch area of the T2 tyre when it was new and unworn was
1219mm². After the tyre had been used for the ULTRA testing its average contact
patch area was 1400mm².
54. 54
Figure 43 - Contact patch analysis on an under inflation tyre
The average contact patch area of the T4 tyre when it was new and unworn was
1364mm² as shown in Figure 42. After the tyre had been used for ULTRA testing its
average contact patch area was 1119mm².
This test has produced an anomaly with the contact area of the worn T4. It appears
that two of the locations on the tyre have much lower contact areas than the other two.
This appears to be an operator error.
6.3 X3 images
6.3.1 Inflation
Figure 43 shows the contact patch of an under inflated T2. The area is very large but
the blue colour indicates that is not pressing hard on the pressure mat. The yellow
areas at either side indicate that it is pushing down harder on the outsides of the tyre
than on the inner area.
55. 55
Figure 44 - Standard loaded tyre with standard inflation
pressure
.
The red areas in Figure 44 show that the inner area of the tyre is causing more
downward pressure on the pressure mat. It can be seen that the contact area is smaller
with the standard inflation.
Figure 45 shows the same tyre overinflated. There is a much smaller contact area,
which was expected, and the smaller area has a large red region indicating that the
pressure in the middle is much higher than previously.
57. 57
Figure 46 - Tyre contact area with standard inflation and
no load
6.3.2 Load
Figure 46 shows the tyre without the standard loading applied, and a red area in the
middle can be seen with yellow areas surrounding it, and blue areas on the outside.
This indicates that the pressure is being applied to the pressure mat the most in the
middle of the contact area, and the further out from there, the less pressure being
applied.
Figure 47 shows a much larger contact area as the standard load has been applied
and is pushing the tyre down to flatten the contact patch on the pressure pad.
The overloaded tyre shows a much larger tyre contact patch area as shown in Figure
48.
58. 58
Figure 47 - Tyre contact area with standard inflation and
standard load
59. 59
Figure 48 - Contact patch of overloaded tyre with standard inflation
pressure
The pressure maps show that the relationship between inflation and contact area is
that lower inflation means higher contact area, and that the relationship between load
and contact area is that the higher the load, the higher the contact area.
61. 61
Figure 49 - Thermal image of tyre showing the heat imprint of the road surface
Discussion
As the load increases on the tyre, and the tyre becomes overloaded, the force pushes
the tyre from a circular shape into a more elliptical one. The deformation as the wheel
spins under load causes the rubber in the tyre to heat up, and also causes the tyre
contact area to increases. The results shown have further evidenced this, clearly when
the load increased on the Griptester wheel the camera picked up higher temperatures
on the tyre and the contact area increased as measured by the pressure mat.
Increasing the speed and the load of the test forces the tyre to change shape at a
quicker rate, as it is constantly being pushed down by the load and pushed on by the
drum speed, meaning that the internal forces of the tyre cause it to get even hotter.
It was discovered on an image of the tyre slowing down, that there is a pattern on the
tyre which shows a heat imprint that almost mirrors the sampling texture that was used
on the ULTRA testing, shown in Figure 39. The hotter brighter areas are assumed to
be the areas of the sample with prominent aggregates that have touched the contact
patch of the tyre, which presumably cause friction on the wearing surface and
resultantly heat these areas up. The darker patches on the tyre are then the gaps
between the aggregates were the macro texture is. These areas looked to be cooler
in relation to the hotter parts as a result of there being no aggregates causing friction
to them, therefore less heating up. It might be assumable that the areas that are hotter
and therefore being caused more friction are the areas that are wearing away faster
62. 62
than the others. It may be possible to draw a relationship between the hotter parts of
the tyre, the parts of the tyre that are being worn most, and how heat is dissipating
from these areas down through the road surface. How this transferred heat then
affects the road surface could also be studied.
One limitation of the experiment is in the creation of merged images as this function
on the X3 software will also merge any anomalies in the 100 images also. This means
that the anomalies will not be taken into account and that they will be used. Perhaps
there were no anomalies on the testing but never-the-less the 100 images and snaps
were all different, meaning that there must some variation. It may have been better to
make a judgement and choose the one out of the 100 that best represents that status
quo than to create an average with possibly flawed data. However, this did not seem
to affect the results significantly as the predicted relationships were still evident in the
results.
64. 64
Conclusions
It appears from the results found through ULTRA testing that there is a consistent
relationship between load and tyre temperature; as the load increases, the tyre
temperature increases. The same can be said for a relationship between speed and
tyre temperature, as the tyre reached higher temperatures as speed was increased.
It would appear that there is a positive relationship between the speed of the test and
the rate at which the tyre heats up.
The relationship between inflation and contact patch is demonstrated with the lower
the inflation, the higher the contact area on the tyre is. There is also a relationship
demonstrated with load and tyre contact patch, as the higher the load was increased,
the higher the area of contact patch was recorded.
66. 66
Recommendations
• An area that could be further researched is the wearing surface of the tyre, in
the way that the heat imprint of road can be seen through a thermographic camera,
and what affect this could have on the wearing of the tyre and the road surface.
• Decreasing the inflation of the tyre should cause more internal flexing on the
wearing surface as it flattens to touch the surface, this means that there will be more
flexing in the tyre and more internal forces heating the tyre up. A study should be
completed to investigate this, with different inflation pressures on a tyre running on the
ULTRA machine.
• Depending on the ambient temperature that the tyre’s environment is, the tyre
will either be hotter or colder to start with. With a tyre starting off at a higher
temperature, say 30°, the temperature should rise higher than what has been shown
here. A study should be completed to investigate whether this is true, and also to see
if the ambient temperature being lowered has a corresponding effect in the opposite
direction.
• How tyre temperature affects the tyre’s elasticity and therefore its skid
resistance.
68. 68
References
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temperature field of steady-state rolling tyres. Journal of Applied Mathematical
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http://www.sciencedirect.com/science/article/pii/S0307904X1300560X.
[Accessed 02 December 2013].
Lei ZHANG, Ghim Ping ONG, Tien Fang FWA, 2013. A Numerical Study on
the Influence of Aggregate Size on Skid Resistance Performance of Porous
Pavements. Proceedings of the Eastern Asia Society for Transportation
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line/proceedings/vol9/PDF/P296.pdf. [Accessed 02 December 2013].
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