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

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Presentation on theme: "Yusuke Minami* Tomoaki Iwai**, Yutaka Shoukaku** * Graduate School of Natural Science and Technology Kanazawa University ** College of Science and Engineering."— Presentation transcript:

1 Yusuke Minami* Tomoaki Iwai**, Yutaka Shoukaku** * Graduate School of Natural Science and Technology Kanazawa University ** College of Science and Engineering Kanazawa University 30 th Annual Conference on Tire Science and Technology September 13-14, 2011 Akron, Ohio, USA

2  1. Introduction and objective  2. Apparatus and method Friction experiment and condition Observation method Observation area  3. Results and discussions Coefficient of friction Observation in leading area Observation in trailing area  4. Conclusions Table of contents

3  1. Introduction and objective  2. Apparatus and method Friction experiment and condition Observation method Observation area  3. Results and discussions Coefficient of friction Observation in leading area Observation in trailing area  4. Conclusions Table of contents

4 Studless Tire Studless tires are designed for use in winter conditions, such as snow and ice Soft tread compound Increase 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

5 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 sipes Various hard materials in tread rubber glass fibers, ceramics, nut shell ・・・ Development of tread compound

6 ・ 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

7 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

8  1. Introduction and objective  2. Apparatus and method Friction experiment and condition Observation method Observation area  3. Results and discussions Coefficient of friction Observation in leading area Observation in trailing area  4. Conclusions Table of contents

9 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

10  60mm 12.5mm Pore Formulation of rubber specimen Natural rubber filled with carbon black Pore diameter, mm No pore,  0.5,  1,  2 TABLE 1 Specification of the rubber specimen FIG.5 Rubber specimen

11 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 TABLE 3 Specification of the fine particles

12 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

13 To distinguish the contact surface against rubber, water, and air. To observe and visualize the water flow 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

14 - The total internal reflection method - When incident light as passes from a medium of high refractive index n 1 to a medium of lower refractive index n 2, ・・・ (1) θ2θ2 Medium 2 FIG. 8 Refraction of light as passes from a medium of high refractive index (n 1 ) to a medium of lower refractive index (n 2 ) θ1’θ1’ θ1θ1 n1n1 n2n2 Incident lightReflected light Refraction light Medium 1 n 1 > n 2

15 θ1’θ1’ θ1θ1 n1n1 n2n2 Incident lightReflected light - The total internal reflection method - θ 2 =90° 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 (n 1 ) to a medium of lower refractive index (n 2 ) n 1 > n 2

16 Incident mediumCritical angle, ° Rubber Water 61 Air 41 TABLE 5 Critical angle as the light passes from the prism Prism 1.52 Rubber Water 1.33 Air 1.0 TABLE 4 Refractive index

17 - The total internal reflection method - water air rubber prism θ1θ1 (a) Cross section (b) Total internal reflection image 41 ° < θ 1 <61 ° FIG. 9 Reflected light and the refracted light at the interface of various refractive indexes θ1θ1 θ1θ1

18 - The total internal reflection method - water air rubber prism (a) Cross section (b) Total internal reflection image 41 ° < θ 1 <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 θ1θ1 θ1θ1 θ1θ1

19 To distinguish the contact surface against rubber, water, and air. To observe and visualize the water flow 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

20 (a) t 1 (b) t 2 (c) Particles at t 2 superimposed on the image at t 1 (d) Movement direction of each particles from t 1 to t 2 - Visualized water flow- FIG. 10 Principle of the particle tracking velocimetry (PTV)

21 (x 3. y 3 ) (x 4. y 4 ) (x 1. y 1 ) (x 2. y 2 ) - Visualized water flow- (a) t 1 (b) t 2 (x 1. y 1 ) (x 3. y 3 ) (x 4. y 4 ) (c) Movement direction of each particles from t 1 to t 2 FIG. 11 PTV considered relative displace between pore and particles Δy (x 2. y 2 )

22 - Visualized water flow- (a) t 1 (b) t 2 (x 1. y 1 ) (x 2. y 2 ) (x 3. y 3 ) (x 4. y 4 ) (c) Movement direction of each particles from t 1 to t 2 (d) Superimposed image considering the relative distance between pore and particles (x 3. y 3 ) (x 1. y 1 ) (x 2. y 2 ) (x 4. y 4 ) FIG. 11 PTV considered relative displace between pore and particles (x 3. y 3 ) (x 4. y 4 ) (x 1. y 1 ) (x 2. y 2 ) Δy (x 1. y 1 -Δy) (x 2. y 2 -Δy) Δy

23 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

24  1. Introduction and objective  2. Apparatus and method Friction experiment and condition Observation method Observation area  3. Results and discussions Coefficient of friction Observation in leading area Observation in trailing area  4. Conclusions Table of contents

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

26 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.

27 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 Sliding direction of rubber

28 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 Sliding direction of rubber 2mm Front edge

29 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 Sliding direction of rubber 2mm Rear edge

30 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. Observation in leading area Sliding direction of rubber

31 2mm (c) 0.6s(d) 0.8s (b) 0.4s (a) 0.2s Sliding direction of rubber air water rubber The front edge became noncontact with the mating prism. Observation in leading area

32 2mm Sliding direction of rubber (a) Orthographic images of particles at time t 2 (b) Displacement of particles and pore from t 1 to t 2 FIG. 15Orthographic image of particles and the flow results of PTV in leading area (iii) t 2 =0.6s (iv) t 2 =0.8s (ii) t 2 =0.4s(i) t 2 =0.2s (iii) From t 1 =0.4s to t 2 =0.6s (ii) From t 1 =0.2s to t 2 =0.4s (i) From t 1 =0s to t 2 =0.2s (iv) From t 1 =0.6s to t 2 =0.8s Observation in leading area

33 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. Observation in leading area

34 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 Observation in leading area

35 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 Sliding direction of rubber

36 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. Observation in trailing area Sliding direction of rubber

37 2mm (c) 0.6s(d) 0.8s (b) 0.4s (a) 0.2s Sliding direction of rubber 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. Observation in trailing area

38 2mm Sliding direction of rubber (a) Orthographic images of particles at the time t 2 (b) Displacement of particles and pore from t 1 to t 2 FIG. 18Orthographic image of particles and the flow results of PTV in trailing area (iii) t 2 =0.6s (iv) t 2 =0.8s (ii) t 2 =0.4s(i) t 2 =0.2s (iii) from t 1 =0.4s to t 2 =0.6s (ii) from t 1 =0.2s to t 2 =0.4s (i) from t 1 =0s to t 2 =0.2s (iv) from t 1 =0.6s to t 2 =0.8s Observation in trailing area

39 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. Observation in trailing area

40 The water flowed along the pore edge and didn’t cross the rear edge. 2mm The 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. Observation in trailing area

41  1. Introduction and Objective  2. Apparatus and method Friction experiment and condition Observation method Observation area  3. Results and discussions Coefficient of friction Observation in leading area Observation in trailing area  4. Conclusions Table of Contents

42 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

43 Thank you for your kind attention

44

45 -Observation of contact area (Leading area)-

46

47 -Observation of contact area (Trailing area)-

48

49 (a) t 1 (b) t 2 (c) Particles at t 2 superimposed on the image at t 1 (d) Movement direction of each particles from t 1 to t 2 ・ Observation method - Visualized water flow-

50 ・ Observation method - Visualized water flow- (a) t 1 (b) t 2 (x 1. y 1 ) (x 2. y 2 ) (x 3. y 3 ) (x 4. y 4 ) (c) Movement direction of each particles from t 1 to t 2 (d) Superimposed image considering the relative distance between pore and particles Δy (x 3. y 3 ) (x 1. y 1 ) (x 2. y 2 ) (x 4. y 4 ) (x 1. y 1 -Δy) (x 3. y 3 ) (x 2. y 2 -Δy) (x 4. y 4 ) FIG. 7 PTV considered relative displace between pore and particles.

51 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 tire Use 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

52 Friction force of Studded Tire Fig Concept of tread pattern design for snow and ice covered road

53 Fig Rate of frictional force under various road condition

54 Rubber friction force Rubber friction force F F = F H +  ( F A + F D ) F H : Hysteresis Friction Energy loss caused by deformation of tread derived from road roughness Rubber Road surface F A : Adhesion Friction Energy loss caused by adhesion between tread and road Rubber Road surface F D : Digging Friction Energy loss caused by scratching road surface and wearing of rubber itself Rubber Road surface  : Friction improving coefficient developed by displacement of water friction

55 Fig. Variation in coefficient of friction with the pore diameter (b)Aspect ratio AR=1 (a)Aspect ratio AR=0.5

56 NR100 ISAF CB2 ZnO4 Stearic acid 2 Antioxidant 2 Oil3 Vulcanization accelerator 1 Sulfur1.5 Composition of rubber specimen


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