Visualising Tread Wear - Guildford TYRE... · • Bulk of tyre treads and Akron test pieces retain good rubber-filler interaction • Wear mechanism for on-the-road tyres not replicated

www.tarrc.co.uk www.rubberconsultants.com

Tun Abdul Razak Research Centre (TARRC) A RESEARCH & PROMOTION CENTRE OF THE MALAYSIAN RUBBER BOARD

Visualising Tread Wear Dr Pamela Martin, Materials Scientist

4th International Tyre Colloquium, April 2015


• Consumers want fuel economy, safety, low cost and long service life.

• Legislators are introducing steps to reduce the impact of transport.

• Growing concerns about climate change and oil price/availability

demands for renewable materials with low carbon footprints.

Tyre Performance

• Resistance to wear is a critical

attribute for tyre performance

EU Tyre label 2012


Passenger tread compounds: • Carbon black substituted with silica filler fuel efficient tires • sSBR/BR silica/silane technology low rolling resistance and improved wet grip • Free of aromatic oil (PAHs) Health and environment

Last 25 Years of Tire Tread Technology

Truck/Bus tread compounds: • NR/BR or NR/SBR blends • Black-filled (Non-rubbers in NR consume or block coupling silane during

silica mixing)


• An ecologically sustainable rubber from renewable resource

• Is more polar than any other tire rubber inherently good interaction with silica

• Has a large negative carbon footprint Rubber trees sequester carbon dioxide

• Suitable for both passenger and commercial vehicles

• Ekoprena-25: Commercial grade 25% epoxidised natural rubber

• Produced by epoxidation of natural rubber latex

Current Developments Tire Tread Technology Industry aims:

• Continual improvements in rolling resistance and wet grip

• Environmental sustainability

Solution:


Truck/Bus Tyre Tread Formulations

Truck/Bus tread compounds: • Ekoprena-25 with 55 phr silica filler, low level of coupling silane • NR/BR (70:30) with 53 phr N234 black

Physical properties matched: • Hardness • Modulus • Tensile strength


• Used in silica-filled tyre treads Ekoprena provides

Silica-filled Ekoprena Tyre Treads

Significantly improved ice grip possibly extending the range of

useable temperatures of low rolling resistance tyres

Very low rolling resistance good fuel economy

Exceptionally high wet grip good safety


Service data

Coach trials – rear drive axle Ca. 18,000 km

52 km/day urban

Akron Abrasion Test

BS 903 A9 1988 Method B 5500 cycles per test at 15° slip angle

250 rpm ± 5 rpm Carborundum & fuller’s earth (2:1)

Techniques Used for Assessing Wear

Correlation of laboratory results to in-service road test results is notoriously poor!


Coach Wear Trials

Tyres fitted on rear drive axle

Tread samples removed after ca. 18,000 km urban usage (52 km/day)

Tyres retreaded at TARRC


Circumferential

direction NR/BR black Ekoprena silica

Worn Truck/Bus Tyre Tread Samples

ca. 0.80 nm depth loss per cycle ca. 1.26 nm depth loss per cycle

LM Macro-texture

Ra = 3.3 μm Ra = 7.3 μm

Periodic abrasion pattern observed No abrasion pattern

Dust and debris on surface


Rubber-silica Interaction by ‘Network Visualization’–TEM: methodology

• Swell vulcanisate in polymerisable monomer, e.g. styrene • Polymerize monomer • Cut ultrathin sections of embedded ‘swollen’ vulcanizate • Stain section to identify rubber unsaturation, or unstained

for estimation of microdispersion • Image via TEM


Sections not stained to see only filler particles Example: Network Visualization TEM

Ekoprena silica

0

20

40

60

80

100

100 1000 10000 100000

Cu

mu

lati

ve f

req

ue

ncy

, %

Aggregate area, nm2

Ekoprena

NR

Particle size distribution


Sections stained to see rubber network

Example: Network Visualization TEM

NR Rubber

Network

Polystyrene

Mesh size relates to physical cross-link density


Sections stained to see rubber network and rubber-filler Interactions Example: Network Visualization TEM

Polystyrene Vacuoles

NR Rubber

Network

Zinc oxide


Vacuole

SBR Rubber Network

Silica

No silane coupling agent Silane coupled


Ladouce, Bomal, Flandin and Labarre

Paper No. 33, ACS Rubber Division Meeting, April 4-6 2000

Rubber Chem. Technol., Vol 76, 145, (2003)

Sections stained to see rubber network and rubber-filler Interactions



SBR

Silica

Relative surface occupied by vacuoles decreased with increasing silane content.

Ladouce, Bomal, Flandin and Labarre

Paper No. 33, ACS Rubber Division Meeting, April 4-6 2000

Rubber Chem. Technol., Vol 76, 145, (2003)

Vacuole

No silane coupling agent

Sections stained to see rubber network and rubber-filler Interactions


Ekoprena silica NR/BR black


• Detached and partially detached particles observed • Larger particle in CB NR/BR sample

TEM (unstained)

Samples styrene swollen and polymerised

Polystyrene

Road dirt




• Voids observed around filler particles – weakened rubber-filler interactions

TEM (stained)


Vacuoles

NR/BR black Ekoprena silica

BR phase

CB

NR phase



• Voids around filler – weakened rubber-filler interactions

Vacuoles

TEM (stained)



Worn Truck/Bus Tyre Tread Samples TEM (stained)

• Voids around filler – weakened rubber-filler interactions

Vacuoles




• Bulk does not show weakened rubber-filler interactions

NR/BR black Ekoprena silica TEM (stained)


Circumferential

direction

Laboratory Wear Performance – Akron

Abrasion Resistance Index 119% ca. 1.3 nm depth loss per cycle

Abrasion Resistance Index 220% ca. 0.7 nm depth loss per cycle

Akron Abrasion Resistance Index relative to Standard 50 phr black-filled NR

LM macro-texture

• Coarser/rougher surface corresponds to higher wear rate • Pitch of ridges changes across test piece




Carborundum & fuller’s earth

Laboratory Wear Performance – Akron

Polystyrene

Filler

Abrasion Resistance Index 119% Abrasion Resistance Index 220%

TEM (stained)


Modeling Tyre Wear Processes

Model: • Movement of tread block surface during revolution of tyre • Deformations of tread surface by road asperities

• Heat generation at surface during tyre use

• Contact and slippage between tyre and road

What might we model for the surface layer?

Image taken from www.thermal-cameras.com

Load


Modeling a Tyre Going Over an Asperity

1 mm radius rigid spherical asperity

Results: • Asperity penetrates rubber by 0.5 mm

vertical displacement (mm)

Model parameters: • Rubber dimensions much larger than contact region • Frictionless contact • Neo-Hookean rubber model


Conclusions

• Wear pattern seen for worn CB-filled NR/BR tyre tread samples

significantly different to that observed for Akron test pieces

• Reduced rubber-filler interaction observed at or near surface of on-

the-road worn tyres not observed for Akron test pieces

• Initiated weaknesses in rubber-filler interaction close to the surface

of on-the-road worn tyres lead to particle detachment

• Bulk of tyre treads and Akron test pieces retain good rubber-filler

interaction

• Wear mechanism for on-the-road tyres not replicated by Akron test

• Modelling the surface layer is of interest


Dr Pamela Martin, Dr Stuart Cook and Mr Paul Brown Thanks to Dr Robin Davies, Kathy Lawrence & Jolanta Bonfante for TEM images

Thanks to Dr Julia Gough for modelling

Visualising Tread Wear

@pmartinTARRC

Tun Abdul Razak Research Centre (TARRC) A RESEARCH & PROMOTION CENTRE OF THE MALAYSIAN RUBBER BOARD

Visualising Tread Wear - Guildford TYRE... · • Bulk of tyre treads and Akron test pieces retain good rubber-filler interaction • Wear mechanism for on-the-road tyres not replicated

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