Dynamic Observation of Contact Behavior between Rubber for Tires and Ice by Refraction Contrast Imaging Studded tires were abolished in 1994 due to environmental problems, such as dust and noise pollution, in Japan. In order to run on ice or snow safely, winter tires called studless tires have been developed and sold. In recent years, many studless tires are available in the market. Studless tires make the surface of an icy road very smooth when they slip on the road, resulting in an icy road with a very low friction coefficient. In addition, the friction between a studless tire and ice is related to the characteristics of the ice, e.g., the crystal structure, the size, the dielectric constant and the concentration of impurities [1,2]. Also, the frictional heat generated between a studless tire and an icy road dissolved the surface of the icy road, and water serves as a lubricant [3]. These friction behaviors become complex under the conditions of the boundary and the fluid lubrication. Nihei et al. have reported about the effects of the surface roughness of a studless tire [4]. According to their report, when the surface roughness was about 50 the friction coefficient became maximum, and they expected that water is probably removed due to surface unevenness. Therefore, a systematic investigation and a detailed analysis of these behaviors are re q uired to improve the performance of studless tires. In this study, we observed and investigated the contact behavior between the rubber for tires and ice. The in situ observation of their behaviors by X- ray refraction contrast imaging caused by the reflection effect was carried out at the third hutch of beamline BL19B2 . A continuous X- ray from the synchrotron radiation source was monochromatized to 2 0 ke V by a Si ( 311 ) double crystal monochromator. In order to perform time - resolved observation, the X- ray detector adopted was a CCD camera with a pixel size of 1 0 μ m (C 4 880 , H amamatsu P hotonics K . K) . The CCD camera was coupled with the optical lens and the phosphor screen. The distance between the sample and the X- ray CCD detector was determined to be about 2 m using the formula [ 5 ], ∆ X = ( λ L ) 1 / 2 , where ∆ X is the space resolution of detection, λ the X- ray wavelength, and L the distance from the sample to the detector. The beam diffuser made by rotating a sandpaper was installed at the first hutch in order to remove interference patterns, probably caused by Fig. 1. Compression-testing machine equipped with a high-precision cooling function. B e windows. The compression - testing machine e q uipped with a high - precision cooling function was prepared (F ig. 1 ) . R ubbers of different surface roughnesses were obtained using various kinds of sandpaper based on the JIS standard. The surface roughnesses of the rubbers were ~ 2 0 μ m, ~ 4 5 μ m, ~ 60 μ m and ~ 9 0 μ m. The rubbers prepared were of 2 l × 1 5 w × 3h h mm 3 . The X- ray refraction contrast imaging data was stored during the process of compressing the sample at a speed of 5 mm / min until the load reached 2 kg / cm 2 . Rubber Rubber Chamber Chamber Compression Compression Ice μ m, 102 ( b) (d) (c) (a) Interfac e Hi royuki Kishimoto Material & Process Technology Research Dept., SRI Research and Development Ltd. E-mail: h-kishimoto.az@srigroup.co.jp Fig. 2. X-ray refraction contrast images under the condition of ice and rubbers contact. The surface roughnesses of the rubbers are (a) 20 μ m, (b) ~ 45 μ m, (c) ~ 60 μ m and (d) 90 μ m. References [ 1] M. Nihei et al. : J idousha G ijutsu Kai Ron b unsyu 25 ( 1 994) 1 4 1. [ 2 ] M. A . Rist: J . Phys. C hem B 101 ( 1 997) 6263 . [ 3 ] M. Nihei et al. : J idousha G ijutsu Kai Ron b unsyu 28 ( 1 997) 89 . [ 4 ] M. Nihei et al. : I nternational Tri b ology C on f e rence ( 1 998) . [ 5 ] Y . Suzuki e t al. : SPIE Proc. 13 ( 1 999) 3770 . T he i mages o f t he co ntact b ehavior b et w ee n ru bb ers o f di ff e rent sur f ace roughnesses and ice are sho w n in F ig. 2 . W hen the sur f ace r oughness is a b out 20 t he r u bb e r and ice are completely in contact, and there is almost no clearance. The de w atering e ff ect could not b e ac q uired at this sur f ace r oughness. A s the sur f ace r oughness increases, the clearance increases due to sur f ace une venness, and then it seems that passages f o r de w atering w ould b e f ormed. O n the other hand, w hen the sur f ace roughness is very large, the f riction coe ff icie nt is small b ecause o f the d rastic decrease in the contact area. Thus, it is very important to o b serve in s itu co ntact b ehaviors b et w ee n the ru bb ers and ice in order to improve the per f ormance o f studess tires. μ m, 3 3 3 3 3 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 103 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10
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