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

30 th Annual Conference on Tire Science and Technology September 13-14, 2011 Akron, Ohio, USA. Observation of Water Behavior in the Contact A rea between Porous R ubber and Mating Surface during Sliding. Yusuke Minami* Tomoaki Iwai**, Yutaka Shoukaku**

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

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  1. 30th Annual Conference on Tire Science and Technology September 13-14, 2011 Akron, Ohio, USA Observation of Water Behavior in the Contact Areabetween Porous Rubber and Mating Surface during Sliding • Yusuke Minami* Tomoaki Iwai**, Yutaka Shoukaku** • * Graduate School of Natural Science and Technology • Kanazawa University • ** College of Science and Engineering • Kanazawa University

  2. Table of contents • 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

  3. Table of contents • 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

  4. Studless Tire Studless tires are designed for use in winter conditions, such as snow and ice Characteristics of studless tires • Soft tread compound • Increase the contact area • A lot of sipes in the tread pattern • Wipe and evacuation the water FIG.1 Tread of studless tire

  5. 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 • Porous rubber is tread compound that has numerious pores both surface and inside. FIG.2 Porous rubber surface

  6. Effect of the porous rubber ・The decrease in elastic modulus of the rubber ・The water removal between tire tread and road surface by water absorption effect of the pores. FIG.3 Water removal image The real contact areabetween the tire and the wet road is believed to be increased

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

  8. Table of contents • 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

  9. Friction experiment and experimental condition A rotating rubber specimen was rubbed against a mating prism. ➢The friction surface between rubber specimen and dove prism is observed through dove prism. 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. ➢The friction force was measured by strain gauges were attached to the parallel leaf spring.

  10. 12.5mm Pore TABLE 1 Specification of the rubber specimen f 60mm FIG.5 Rubber specimen

  11. Syringe TABLE 2 Experimental condition Pure water TABLE 3 Specification of the fine particles Rolling direction Mating prism Rubberspecimen FIG.6 Cross section of contact surface between the prism and the rubber specimen

  12. Observation method (a)Total internal reflection method (b) Orthographic method FIG.7 Optical systems for the contact area measurement: 1, rubber specimen; 2, dove prism; 3, CCD camera; 4, light sources.

  13. To observe and visualize the water flow To distinguish the contact surface against rubber, water, and air. (a)Total internal reflection method (b) Orthographic method FIG.7 Optical systems for the contact area measurement: 1, rubber specimen; 2, dove prism; 3, CCD camera; 4, light sources.

  14. - The total internal reflection method - n1 > n2 When incident light as passes from a medium of high refractive index n1 to a medium of lower refractive index n2, Medium1 Incidentlight Reflectedlight θ1 θ1’ ・・・(1) n1 n2 θ2 Medium 2 Refractionlight FIG. 8 Refraction of light as passes from a medium of high refractive index (n1) to a medium of lower refractive index (n2)

  15. - The total internal reflection method - n1 > n2 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 qc was determined as follow: Medium1 Incidentlight Reflectedlight θ1 θ1’ n1 n2 θ2=90° 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) ・・・(2)

  16. TABLE 4 Refractive index TABLE 5 Critical angle as the light passes from the prism

  17. - The total internal reflection method - rubber water air prism θ1 θ1 θ1 41° < θ1 <61° (a) Cross section (b) Total internal reflection image FIG. 9 Reflected light and the refracted light at the interface of various refractive indexes

  18. - The total internal reflection method - rubber water air prism θ1 θ1 θ1 41° < θ1 <61° (a) Cross section (b) Total internal reflection image The differences of intensity of the reflected light allow distinction of contact surface variation FIG. 9 The reflected light and the refracted light at the interface of various refractive indexes

  19. To observe and visualize the water flow To distinguish the contact surface against rubber, water, and air. (a)Total internal reflection method (b) Orthographic method FIG.7 Optical systems for the contact area measurement: 1, rubber specimen; 2, dove prism; 3, CCD camera; 4, light sources.

  20. -Visualized water flow- (a) t1 (b) t2 (c) Particles at t2 superimposed on the image at t1 (d) Movement direction ofeach particles from t1 to t2 FIG. 10 Principle of the particle tracking velocimetry (PTV)

  21. -Visualized water flow- (x2. y2) (x2. y2) (x1. y1) (x1. y1) (x4. y4) (x4. y4) (x3. y3) (x3. y3) (a) t1 (b) t2 Δy (c) Movement direction of each particles from t1 to t2 FIG. 11 PTV considered relative displace between pore and particles

  22. -Visualized water flow- (x2. y2) (x1. y1) (x4. y4) (x3. y3) (a) t1 (b) t2 (x4. y4) (x2. y2) (x2. y2) (x1. y1) (x1. y1) (x4. y4) Δy Δy (x3. y3) (x3. y3) (x2. y2-Δy) (x1. y1-Δy) (c) Movement direction of each particles from t1 to t2 (d) Superimposed image considering the relative distance between pore and particles FIG. 11 PTV considered relative displace between pore and particles

  23. Observation area Mating prism Leading area The surface transitioned from noncontact to contact with the mating prism. Trailing area The surface of transitioned from contact to noncontact with the mating prism. Rolling direction Rubberspecimen FIG. 12 Definition of the area of contact

  24. Table of contents • 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

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

  26. Coefficient of friction The coefficient of friction of the rubber specimen with pores was larger than that of the rubber specimen without pores. Fig. 12 Variation in coefficient of friction with the pore diameter under wet conditions

  27. Observation in leading area 2mm (a) 0.2s 2mm (b) 0.4s Sliding direction of rubber (c) 0.6s (d) 0.8s FIG. 14 Rubber surface of leading area observed by the total internal reflection method

  28. Observation in leading area Front edge 2mm (a) 0.2s 2mm (b) 0.4s Sliding direction of rubber (c) 0.6s (d) 0.8s FIG. 14 Rubber surface of leading area observed by the total internal reflection method

  29. Observation in leading area Rear edge 2mm (a) 0.2s 2mm (b) 0.4s Sliding direction of rubber (c) 0.6s (d) 0.8s FIG. 14 Rubber surface of leading area observed by the total internal reflection method

  30. Observation in leading area water air rubber (a) 0.2s (b) 0.4s 2mm 2mm Sliding direction of rubber (c) 0.6s (d) 0.8s water and air exist coincide in the pore The pore contained an air bubble during the sliding.

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

  32. Observation in leading area (iv) t2=0.8s (i) t2=0.2s (ii) t2=0.4s (iii) t2=0.6s 2mm (a) Orthographic images of particles at time t2 Sliding direction of rubber (i) From t1=0s to t2=0.2s (ii) From t1=0.2s to t2=0.4s (iv) From t1=0.6s to t2=0.8s (iii) From t1=0.4s to t2=0.6s (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

  33. Observation in leading area The water did not intrude into the pore when the pore was rubbed. The water flowing along the edge of pore was observed. FIG.16 Superimposed image considering the relative distance between pore and particles

  34. Observation in leading area water air rubber 2mm 2mm The pore contained the air bubble during the sliding. 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.

  35. Observation in trailing area 2mm (a) 0.2s 2mm (b) 0.4s Sliding direction of rubber (c) 0.6s (d) 0.8s FIG. 17 Rubber surface of trailing area observed by the total internal reflection method

  36. Observation in trailing area 2mm (a) 0.2s (b) 0.4s 2mm Sliding direction of rubber (c) 0.6s (d) 0.8s The air in the pore remained even if the pore left the prism.

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

  38. Observation in trailing area (iv) t2=0.8s (i) t2=0.2s (ii) t2=0.4s (iii) t2=0.6s 2mm (a) Orthographic images of particles at the time t2 Sliding direction of rubber (i) from t1=0s to t2=0.2s (ii) from t1=0.2s to t2=0.4s (iv) from t1=0.6s to t2=0.8s (iii) from t1=0.4s to t2=0.6s (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

  39. Observation in trailing area The water flowed along the pore edge. No particles were observed to cross the rear edge. FIG. 19 Superimposed image considering the relative distance between pore and particles

  40. Observation in trailing area 2mm 2mm The rear edge of the pore contacted with mating prism even if the pore left the mating prism. The water flowed along the pore edge and didn’t cross the rear edge. The rear edge of the pore was probably rubbed strongly against the prism and wiped the water.

  41. Table of Contents • 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

  42. Conclusions 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.

  43. Thank you for your kind attention

  44. -Observation of contact area (Leading area)-

  45. -Observation of contact area (Trailing area)-

  46. ・Observationmethod -Visualized water flow- (a) t1 (b) t2 (c) Particles at t2 superimposed on the image at t1 (d) Movement direction ofeach particles from t1 to t2

  47. ・Observationmethod -Visualized water flow- (x2. y2) (x1. y1) (x4. y4) (x3. y3) (a) t1 (b) t2 (x4. y4) (x4. y4) (x2. y2) (x1. y1) Δy (x3. y3) (x3. y3) (x2. y2-Δy) (x1. y1-Δy) (c) Movement direction of each particles from t1 to t2 (d) Superimposed image considering the relative distance between pore and particles FIG. 7 PTV considered relative displace between pore and particles.

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