Fundamental Study of Friction with Hierarchically Ruga-controlled Surfaces

该奖项支持适用于现代纳米技术以及岩土科学和工程的摩擦力学基础研究。自达芬奇时代以来，摩擦——两个物体之间的滑动阻力——一直是最具挑战性的主题之一，人们对它的理解仍然不完整，但对现代科学技术的进步至关重要。例如，它在控制纳米机械臂的滑动机制，以及测量和预测构造断层线上形成的力方面至关重要。在此，首席研究员计划开发一种创新的力学框架-摩擦的重整化，即用较小长度尺度的摩擦行为连续评估较大长度尺度的摩擦，并通过对照实验进行验证。本课题的基础研究将建立纳米尺度摩擦调控的系统框架，以控制宏观摩擦。摩擦力的多尺度框架不仅对纳米机械装置技术的发展，而且对机器人和生物医疗装置工程中的摩擦控制技术的发展，以及解决地质科学问题都是必不可少的。它还将提高对摩擦控制敏感的制造过程的计算建模和设计能力，这在生产行业中广泛遇到。此外，在这个项目下，首席研究员将在布朗大学制定一个外展计划，通过暑期实习计划教育代表性不足的学生，并开发新的课程材料。在过去的25年中，对多尺度摩擦过程的研究非常活跃，以揭示这些过程的分子起源，并在不同长度尺度上对现象的理解建立桥梁。最近，首席研究小组发现，摩擦的重整化软化/强化取决于分子粘接摩擦应力的减少、与尺度相关的凹凸不平的平坦化或表面的硬化。这种独特的摩擦重整化方案在研究粗糙表面的多尺度摩擦过程中非常有效。有了这笔奖金，首席研究员将研究：(1)粗糙表面摩擦的重整化强化；Ruga（表面波纹）控制等级粗糙度以研究摩擦的重整化；（iii）粗糙度谱的演变和由于粗糙塑性和磨损而产生的摩擦。

This award supports fundamental research on the mechanics of friction applicable to modern nanotechnology as well as geotechnical science and engineering. Since the time of Leonardo da Vinci, friction - sliding resistance between two objects - has been one of the most challenging subjects still incomplete in understanding but crucial in advancement of modern science and technology. For example, it is critical in controlling sliding mechanisms in nano-manipulators as well as in measuring and predicting forces building up at tectonic fault lines. Here, the principal investigator plans to develop an innovative mechanics framework - renormalization of friction, i.e. successive evaluation of larger length scale friction with smaller length scale friction behavior, and verify it with controlled experiments. The fundamental studies of this project will establish a systematic framework for regulating nanoscale friction to control macroscopic friction. The multi-scale framework of friction will be essential for developing not only nano-mechanical device technology but also friction-control technology in robotics and bio-medical device engineering, as well as for solving scientific problems in geology. It will also advance computational modeling and design capabilities for manufacturing processes sensitive to friction control, widely encountered in production industries. In addition, under this project, the principal investigator will develop an outreach program at Brown, to educate underrepresented students through summer internship programs, and to develop new course material.Over the past two and half decades, research on multi-scale frictional processes has been very active to uncover the molecular origin of these processes and to bridge understanding of the phenomena at different length scales. Recently the principal investigator's group revealed that renormalization softening/strengthening of friction develops depending on the reduction of molecular adhesive friction stress, scale-dependent flattening of asperities or stiffening of the surface. This unique scheme of friction renormalization is very powerful in investigating multi-scale friction processes of rough surfaces. With this award, the principal investigator will study (i) renormalization strengthening in rough-surface friction; (ii) Ruga (surface corrugation) control of hierarchical roughness to study renormalization of friction; (iii) evolution of roughness spectra and friction due to asperity plasticity and wear.