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.
