【中文摘要】表面是物体间力传递的重要渠道。随着现代材料的复杂化和微型化，表面和界面也往往成了能量耗散、结构失效等众多关键力学现象最集中发生的地方。申请人近些年通过微纳米尺度力学实验与理论和数值模拟相结合的手段，对不同材料（如二维材料、岩石、石墨等）表面摩擦的微观机制进行了研究。研究在摩擦行为的实验表征以及微观机制的揭示方面取得了一些新的进展，成果发表在Science、Nature、Nature Materials、Physical Review Letters等期刊。基于前期研究，本项目拟从岩石材料入手对接触界面的一种重要演化行为——摩擦“老化”现象展开进一步研究。本课题将从实验上进一步区分和确定摩擦“老化”现象的不同物理机制，并尝试建立多尺度力学模型来描述摩擦“老化”这一具有尺寸效应的力学行为。研究结果将有助于人们进一步认识和改进现有的唯象摩擦模型，为建立基于物理微观机制的新一代摩擦理论提供支持。【英文摘要】Materials interact with each other primarily through their surfaces. As modern materials and systems are getting more and more complicated and miniaturized, surfaces and interfaces are becoming the places where a substantial degree of energy dissipation, structural instabilities, and other interesting mechanical phenomena take place. In recent years, the applicant has explored the physical mechanisms of friction of various materials (e.g. 2D materials, rock, graphite, etc) via combining micro- and nano-scale experiments with theoretical modeling and numerical simulations. Research studies have led to discovery of many unique frictional behaviors and development of several new friction theories. The results have been published on journals like Science, Nature, Nature Materials and Physical Review Letters. In this proposed work, frictional ageing, the key evolution behavior of friction, will be systematically studied using rock materials as a typical example. More specifically, we will validate different mechanisms that were proposed to govern the ageing behavior through multi-scale friction experiments. Based on the discovered physical mechanism(s), we aim to construct a multi-scale mechanics model to describe the length-scale-dependent frictional ageing behavior. These results may lead to better understandings of the existing empirical rate-and-state friction laws, which eventually will be beneficial for establishing more consistent and physically-meaningful friction theories in the future.