Physics of Friction

两个固体表面之间的滑动摩擦是我们日常生活中的一个重要问题，自古以来就被研究过。微纳米尺度的摩擦研究是近年来才开始的，受到广泛关注。在固体中观察到类似于两个固体表面之间滑动摩擦的摩擦现象，如钉扎和密度波和磁通晶格的动力学。这些不同的摩擦现象有许多共同的性质，但也有其特殊性。这些现象的物理学甚至在基本方面也不清楚。在这个研究项目中，我们研究了不同尺度的摩擦现象，试图统一地理解它们，并通过适用于每个尺度的摩擦现象的有效模型来明确摩擦的普遍性和多样性。我们得到了以下结果。i)我们研究了一个固体中所有原子都固定的二维模型，得到了以下结果。运动的方向可能会偏离外力的方向。随机性可以使摩擦力变小。这个体系有一种特殊的秩序，即所谓的布拉格玻璃。运动中的系统对垂直于运动的外力具有有限的静摩擦力。ii)建立了一个有效的模型，通过密度波动来描述润滑油分子的行为。在此模型的基础上，我们发现了一种新的现象，即润滑油分子晶体有序度的提高使摩擦力减小。3)石墨是最重要的摩擦系数小的固体润滑剂之一。通过对石墨薄片与石墨衬底摩擦的数值模拟，再现了实验中观察到的小摩擦系数，并明确了其机理。并对石墨摩擦显微镜实验的载荷依赖性进行了解释。4)各种摩擦现象可以用带钉钉的弹性流形模型来表示。然而，在模型中不能考虑塑性的影响。通过对考虑塑性效应的模型进行详细分析，明确了塑性效应的特殊行为及其机理。少

Sliding friction between two solid surface is an important issue in our daily life and has been investigated from ancient age. Investigation of friction in micro and nano scales starts recently and attracts much attention. Frictional phenomena similar to the sliding friction between two solid surface are observed in solids, such as pinning and dynamics of density waves and magnetic flux lattice. These various frictional phenomena have many common properties but also particularities. Physics of these phenomena is not clear even in fundamental aspects.In this research project we studied frictional phenomena of various scales, attempt to understand them in a unified way and make clear the universality and variety of friction by employing effective model suitable to each scale of frictional phenomena. We got the following results.i) We investigated the 2-dimensional model, in which all atoms in one solid are fixed, and obtained the following results.The direction of motion can deviate from … More that of the external force.Randomness can make small the frictional force.The system has a peculiar order, the so called Bragg glass.The system in motion has finite static frictional force against the external force perpendicular to the motion.ii) We developed an effective model, which describes the behavior of the lubricant molecule by means of their density fluctuation. Based on the model we discovered a novel phenomena in which the enhancement of crystal order of the lubricant molecules diminishes the frictional force.iii) Graphite is one of the most important solid lubricants with small frictional coefficient. By numerical simulation of the friction of graphite flakes and graphite substrate we reproduced the small frictional coefficient observed in experiments and made clear its mechanism. We also explained the load-dependence of the frictional force microscope experiment of graphite.iv) Various frictional phenomena can be expressed by elastic manifold model with pinning. The effects of plasticity is, however, can not be taken into account in the model. By detailed analysis of the model which take into account the effects of plasticity, we made clear peculiar behavior of the effects and its mechanism. Less