Yusuke Minami* Tomoaki Iwai, Yutaka Shoukaku * Graduate School of Natural Science and Technology...

Yusuke Minami* Tomoaki Iwai**, Yutaka Shoukaku**

* Graduate School of Natural Science and TechnologyKanazawa University

** College of Science and EngineeringKanazawa University

30th Annual Conference on Tire Science and TechnologySeptember 13-14, 2011Akron, Ohio, USA

1. Introduction and objective

2. Apparatus and methodFriction experiment and conditionObservation methodObservation area

3. Results and discussionsCoefficient of frictionObservation in leading areaObservation in trailing area

4. Conclusions

Table of contents




4. Conclusions

Table of contents

Studless Tire

Studless tires are designed for use in winter conditions, such as snow and ice

Soft tread compoundIncrease the contact area

A lot of sipes in the tread pattern

Wipe and evacuation the water

Characteristics of studless tires

FIG.1 Tread of studless tire

FIG.2 Porous rubber surface

Porous rubber is tread compound that has numerious pores both surface and inside.

The tread rubber of studless tire has been devised in various ways.

Design of tread pattern and sipesVarious hard materials in tread rubber

glass fibers, ceramics, nut shell ・・・Development of tread compound

・ The water removal between tire tread and road surface by water absorption effect of the pores.

Effect of the porous rubber

FIG.3 Water removal image

The real contact area between the tire and the wet road is believed to be increased

・ The decrease in elastic modulus of the rubber

The removal of the water for absorption by the pores on surface of porous rubber, as the details of the process was not clearly understood.

The purpose of this study was to clarify the effect of water absorption by the pores in contact area during sliding under wet conditions.

Objective




4. Conclusions

Table of contents

FIG. 4 Experimental apparatus:1, weight; 2, rubber specimen; 3, dove prism; 4, parallel leaf spring; 5, strain gauge; 6, prism holder;7, linear guide.

A rotating rubber specimen was rubbed against a mating prism.

➢The friction force was measured by strain gauges were attached to the parallel leaf spring.

➢The friction surface between rubber specimen and dove prism is observed through dove prism.

Friction experiment and experimental condition

60mm

12.5mm

Pore

Formulation of rubber specimen

Natural rubber filled with carbon black

Pore diameter, mmNo pore, 0.5, 1,

2

TABLE 1 Specification of the rubber specimen

FIG.5 Rubber specimen

Rolling direction

Rubber specimen

Mating prism

Syringe

FIG.6 Cross section of contact surface between the prism and the rubber specimen

Sliding speed v, mm/s

3-30

Normal load, N 14.7

TABLE 2 Experimental condition

Pure water

material calcium carbonate

diameter, m 50-80

TABLE 3 Specification of the fine particles

Observation method

FIG.7 Optical systems for the contact area measurement: 1, rubber specimen; 2, dove prism; 3, CCD camera; 4, light sources.

(a)Total internal reflection method (b) Orthographic method

To distinguish the contact surface against rubber, water, and air.

To observe and visualize the water flow



- The total internal reflection method -

When incident light as passes from a medium of high refractive index n1 to a medium of lower refractive index n2,

2211 sinsin nn ・・・ (1)

θ2Medium 2

FIG. 8 Refraction of light as passes from a medium of high refractive index (n1) to a medium of lower refractive index (n2)

θ1’θ1

n1

n2

Incident light Reflected light

Refraction light

Medium 1

n1 > n2

θ1’θ1

n1

n2

Incident light Reflected light


θ2=90°

1

21sinn

nc

Incident angle is increasing, the reflected angle becomes right angle and the incident light completely reflected.

Now, the incident angle is called the critical angle. Based on Eq. (1), the critical angle c was determined as follow:

・・・ (2)

Medium 1

Medium 2

FIG. 8 Refraction of light as passes from a medium of high refractive index (n1) to a medium of lower refractive index (n2)

n1 > n2

Incident medium Critical angle, °

Rubber 83-90

Water 61

Air 41

TABLE 5 Critical angle as the light passes from the prism

Prism 1.52

Rubber 1.51-1.52

Water 1.33

Air 1.0

TABLE 4 Refractive index


water airrubber

prism

θ1

(a) Cross section

(b) Total internal reflection image

41° < θ1 <61°

FIG. 9 Reflected light and the refracted light at the interface of various refractive indexes

θ1 θ1


water airrubber

prism

(a) Cross section

(b) Total internal reflection image

41° < θ1 <61°

FIG. 9 The reflected light and the refracted light at the interface of various refractive indexes

The differences of intensity of the reflected light allow distinction of contact surface variation

θ1 θ1 θ1

To distinguish the contact surface against rubber, water, and air.

To observe and visualize the water flow



(a) t1 (b) t2

(c) Particles at t2 superimposed on the image at t1

(d) Movement direction of each particles from t1 to t2

- Visualized water flow-

FIG. 10 Principle of the particle tracking velocimetry (PTV)

(x3. y3)

(x4. y4)(x1. y1)

(x2. y2)


(a) t1 (b) t2

(x1. y1)

(x3. y3)

(x4. y4)

(c) Movement direction of each particles from t1 to t2

FIG. 11 PTV considered relative displace between pore and particles

Δy

(x2. y2)


(a) t1 (b) t2

(x1. y1)(x2. y2)

(x3. y3)

(x4. y4)


(d) Superimposed image considering the relative distance between pore and particles

(x3. y3)

(x1. y1) (x2. y2)(x4. y4)

FIG. 11 PTV considered relative displace between pore and particles

(x3. y3)

(x4. y4)(x1. y1)

(x2. y2)

Δy

(x1. y1-Δy) (x2. y2-Δy)

Δy

Rubber specimen

The surface transitioned from noncontact to contact with the mating prism.

The surface of transitioned from contact to noncontact with the mating prism.

Leading area

Trailing area

Mating prism

FIG. 12 Definition of the area of contact

Observation area

Rolling direction




4. Conclusions

Table of contents

FIG. 13 Variation in coefficient of friction with the pore diameter under wet conditions

Coefficient of friction

Fig. 12 Variation in coefficient of friction with the pore diameter under wet conditions

Coefficient of friction

The coefficient of friction of the rubber specimen with pores was larger than that of the rubber specimen without pores.

2mm

2mm

(c) 0.6s (d) 0.8s

(b) 0.4s(a) 0.2s

FIG. 14 Rubber surface of leading area observed by the total internal reflection method

Observation in leading area

Slid

ing

dire

ctio

n of

rub

ber

2mm

(c) 0.6s (d) 0.8s

(b) 0.4s(a) 0.2s



Slid

ing

dire

ctio

n of

rub

ber

2mm

Front edge

2mm

(c) 0.6s (d) 0.8s

(b) 0.4s(a) 0.2s



Slid

ing

dire

ctio

n of

rub

ber

2mm

Rear edge

2mm

2mm

(c) 0.6s (d) 0.8s

(b) 0.4s(a) 0.2s

air

water

rubber

water and air exist coincide in the pore

The pore contained an air bubble during the sliding.


Slid

ing

dire

ctio

n of

rub

ber

2mm

2mm

(c) 0.6s (d) 0.8s

(b) 0.4s(a) 0.2s

Slid

ing

dire

ctio

n of

rub

berair

water

rubber

The front edge became noncontact with the mating prism.


2mm

Slid

ing

dire

ctio

n of

rub

ber

(a) Orthographic images of particles at time t2

(b) Displacement of particles and pore from t1 to t2

FIG. 15 Orthographic image of particles and the flow results of PTV in leading area

(iii) t2=0.6s (iv) t2=0.8s(ii) t2=0.4s(i) t2=0.2s

(iii) From t1=0.4s to t2=0.6s

(ii) From t1=0.2s to t2=0.4s

(i) From t1=0s to t2=0.2s

(iv) From t1=0.6s to t2=0.8s


FIG.16 Superimposed image considering the relative distance between pore and particles

The water did not intrude into the pore when the pore was rubbed.

The water flowing along the edge of pore was observed.


The water flow detouring the pore is due to the air bubble in the pore. The air bubble in the pore pushed aside the water.

The water flowing along the edge of pore was observed.

air

water

rubber

The pore contained the air bubble during the sliding.

2mm

2mm


2mm

2mm

(c) 0.6s (d) 0.8s

(b) 0.4s(a) 0.2s

FIG. 17 Rubber surface of trailing area observed by the total internal reflection method

Observation in trailing area

Slid

ing

dire

ctio

n of

rub

ber

2mm

2mm

(c) 0.6s (d) 0.8s

(b) 0.4s(a) 0.2s

The air in the pore remained even if the pore left the prism.


Slid

ing

dire

ctio

n of

rub

ber

2mm

2mm

(c) 0.6s (d) 0.8s

(b) 0.4s(a) 0.2s

Slid

ing

dire

ctio

n of

rub

ber

The front edge was not contact with the mating prism as with leading area, and the rear edge of the pore contacted with mating prism even if the pore left the mating prism.


2mm

Slid

ing

dire

ctio

n of

rub

ber

(a) Orthographic images of particles at the time t2

(b) Displacement of particles and pore from t1 to t2

FIG. 18 Orthographic image of particles and the flow results of PTV in trailing area

(iii) t2=0.6s (iv) t2=0.8s(ii) t2=0.4s(i) t2=0.2s

(iii) from t1=0.4s to t2=0.6s

(ii) from t1=0.2s to t2=0.4s

(i) from t1=0s to t2=0.2s

(iv) from t1=0.6s to t2=0.8s


FIG. 19 Superimposed image considering the relative distance between pore and particles

The water flowed along the pore edge.

No particles were observed to cross the rear edge.


The water flowed along the pore edge and didn’t cross the rear edge.

2mm

2m

mThe rear edge of the pore contacted with mating prism even if the pore left the mating prism.

The rear edge of the pore was probably rubbed strongly against the prism and wiped the water.


1. Introduction and Objective



4. Conclusions

Table of Contents

1. The coefficient of friction of the rubber specimen with pores was larger than that of without pores under wet condition.

2. The pore contained an air bubble during sliding under wet condition.

3. The front edge of the pore was not contact with the mating prism. On the other hand, the rear edge of the pore contacted with mating prism even if the pore left the mating prism.

4. The water flow detouring the air bubble in the pore was also observed.

Conclusions

Thank you for your kind attention

-Observation of contact area (Leading area)-

-Observation of contact area (Trailing area)-

(a) t1 (b) t2

(c) Particles at t2 superimposed on the image at t1

(d) Movement direction　　 of each particles from t1 to t2

・ Observation method- Visualized water flow-

・ Observation method- Visualized water flow-

(a) t1 (b) t2

(x1. y1)(x2. y2)

(x3. y3)

(x4. y4)


(d) Superimposed image considering the relative distance between pore and particles

Δy

(x3. y3)

(x1. y1) (x2. y2)

(x4. y4)

(x1. y1-Δy)

(x3. y3)

(x2. y2-Δy)

(x4. y4)

FIG. 7 PTV considered relative displace between pore and particles.

Studded Tire

Roughening the ice

Providing better frivtion between the ice and the soft rubber

Increased the road wear by the studs

Characteristics of studded tires

FIG Studded tireUse of studs is regulated in most countries, and even prohibited in some located

Studless tires are designed for use in winter conditions, such as snow and ice

Friction force of Studded Tire

Fig Concept of tread pattern design for snow and ice covered road

Fig Rate of frictional force under various road condition

Rubber friction force

Rubber friction force FF = FH + ( FA + FD)

FH : Hysteresis Friction

Energy loss caused by deformation of tread derived from road roughness

Rubber

Road surface

FA : Adhesion FrictionEnergy loss caused by adhesion between tread and road

Rubber

Road surface

FD : Digging FrictionEnergy loss caused by scratching road surface and wearing of rubber itself

Rubber

Road surface

: Friction improving coefficient developed by displacement of water friction

Fig. Variation in coefficient of friction with the pore diameter

(b)Aspect ratio AR=1(a)Aspect ratio AR=0.5

NR 100ISAF CB 2

ZnO 4Stearic acid 2Antioxidant 2

Oil 3Vulcanization accelerator

1

Sulfur 1.5

Composition of rubber specimen

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Yusuke Minami* Tomoaki Iwai**, Yutaka Shoukaku** * Graduate School of Natural Science and Technology...

Documents

Yusuke Minami* Tomoaki Iwai, Yutaka Shoukaku * Graduate School of Natural Science and Technology...