Physics of Friction

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，自古就有研究。微纳尺度下的摩擦研究起步较晚，引起了人们的广泛关注。在固体中观察到类似于固体表面滑动摩擦的摩擦现象，如密度波和磁通晶格的钉扎和动力学。这些各种各样的摩擦现象既有许多共同的性质，也有其特殊性。在这个研究项目中，我们研究了不同尺度的摩擦现象，试图以统一的方式理解它们，并通过采用适合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是固定的二维模型，得到了以下结果：运动方向可能偏离…更多的是外力。随机性可以使摩擦力变小。系统有一个特殊的顺序，即所谓的布拉格玻璃。运动中的系统对垂直于运动的外力有有限的静摩擦力。ii)我们发展了一个有效的模型，通过润滑剂分子的密度涨落来描述其行为。基于该模型，我们发现了一种新的现象，即润滑剂分子晶体有序性的增强减小了摩擦力。3)石墨是最重要的固体润滑剂之一，摩擦系数很小。通过对石墨片与石墨片之间摩擦的数值模拟，再现了实验中观察到的小摩擦系数，并对其机理进行了探讨。我们还解释了石墨石摩擦力显微镜实验的载荷依赖性。iv)各种摩擦现象可以用带钉扎的弹性流形模型来表示。然而，该模型不能考虑塑性的影响。通过对考虑塑性影响的模型的详细分析，明确了这些影响的特殊行为及其作用机理。较少

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