Rubber friction: The contribution from the area of real contact.
Rubber friction: The contribution from the area of real contact.
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DOI：
10.1063/1.5037136
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发表时间：
2018-06
期刊：
影响因子：
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通讯作者：
A. Tiwari;N. Miyashita;N. Espallargas;B. Persson
中科院分区：
文献类型：
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作者：
A. Tiwari;N. Miyashita;N. Espallargas;B. Persson
当橡胶块在坚硬且粗糙的基底表面上滑动时，摩擦力有两个贡献，即来自真实的接触面积A的贡献Fad = τf A和来自基底粗糙体施加在橡胶块上的脉动力的粘弹性贡献Fvisc。在这里，我们提出了在不同的滑动速度和温度下获得的实验结果，我们表明，温度高于橡胶玻璃化转变温度Tg的剪切应力τf的温度依赖性比体积粘弹性模量弱。讨论了T > Tg时τf的物理来源，提出其温度依赖性是由滑动界面处橡胶分子链段的迁移率决定的，由于短波长表面粗糙度增加了自由体积效应，滑动界面处的橡胶分子链段迁移率高于本体中的橡胶分子链段迁移率。这与经常观察到的纳米厚玻璃状聚合物表面层的玻璃化转变温度降低是一致的。对于温度T < Tg，剪切应力τf几乎与速度无关，并且与玻璃态聚合物（如PMMA或聚乙烯）的观察结果相似。在这种情况下，橡胶在粗糙接触区域中经历塑性变形，并且接触面积由橡胶渗透硬度确定。对于这种情况下，我们建议，摩擦剪应力是由于在橡胶和转移膜之间的界面处的滑移吸附在混凝土表面上。
There are two contributions to the friction force when a rubber block is sliding on a hard and rough substrate surface, namely, a contribution Fad = τf A from the area of real contact A and a viscoelastic contribution Fvisc from the pulsating forces exerted by the substrate asperities on the rubber block. Here we present experimental results obtained at different sliding speeds and temperatures, and we show that the temperature dependency of the shear stress τf, for temperatures above the rubber glass transition temperature Tg, is weaker than that of the bulk viscoelastic modulus. The physical origin of τf for T > Tg is discussed, and we propose that its temperature dependency is determined by the rubber molecule segment mobility at the sliding interface, which is higher than in the bulk because of increased free-volume effect due to the short-wavelength surface roughness. This is consistent with the often observed reduction in the glass transition temperature in nanometer-thick surface layers of glassy polymers. For temperatures T < Tg, the shear stress τf is nearly velocity independent and of similar magnitude as observed for glassy polymers such as PMMA or polyethylene. In this case, the rubber undergoes plastic deformations in the asperity contact regions and the contact area is determined by the rubber penetration hardness. For this case, we propose that the frictional shear stress is due to slip at the interface between the rubber and a transfer film adsorbed on the concrete surface.