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。自列奥纳多达芬奇时代以来，摩擦力--两个物体之间的滑动阻力--一直是最具挑战性的课题之一，尽管人们对它的认识还不完全，但它对现代科学技术的进步至关重要。例如，它在控制纳米操纵器的滑动机制以及测量和预测构造断层线上的作用力方面至关重要。在这里，首席研究员计划开发一个创新的力学框架-摩擦重整化，即用较小的长度尺度摩擦行为连续评估较大的长度尺度摩擦，并通过受控实验进行验证。本项目的基础研究将建立一个调控纳米尺度摩擦力以控制宏观摩擦力的系统框架。摩擦的多尺度框架将是必不可少的，不仅发展纳米机械设备技术，而且在机器人和生物医疗设备工程中的摩擦控制技术，以及解决地质科学问题。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存在。此外，在该项目下，首席研究员将在布朗大学开展一项外展计划，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年里，多尺度摩擦过程的研究一直非常活跃，以揭示这些过程的分子起源，并在不同长度尺度上理解现象。最近的主要研究人员的小组透露，重整化软化/加强摩擦的发展取决于分子粘附摩擦应力的减少，尺度相关的平坦化的凹凸不平或硬化的表面。这一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是非常有效的。凭借该奖项，首席研究员将研究（i）粗糙表面摩擦的重整化强化;（ii）分级粗糙度的Ruga（表面粗糙度）控制，以研究摩擦的重整化;（iii）粗糙度谱的演变和由于粗糙度塑性和磨损引起的摩擦。

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.