This award supports the study of the physical mechanisms that underlie friction using mathematical modeling and experiments. Friction is the resistance to sliding between two solid surfaces that are in mechanical contact. These mechanisms operate at sub-micrometer length scales and involve complex mechanical interactions that are dictated by the surfaces' adhesion and roughness. The specifics of these mechanisms, however, remain poorly understood. The new knowledge will lead to new strategies that can reduce energy wastage, for example in engines, due to friction. Additionally, the new knowledge in alliance with micro-fabrication techniques will allow engineers to create surfaces with tailored or tunable surface properties. Specifically, it will inform them which sizes, shapes and arrangements of surface features should be used in order to produce the desired frictional effects. Such "structural surface engineering" has the potential to galvanize scientific and technological breakthroughs in many disciplines. For example, it can drive the development of prosthetics that are capable of the human sense of touch, and increase the agility of the next generation of climbing robots for search and rescue missions.
The new knowledge will be derived by investigating the hypothesis that a significant fraction of friction involving elastomeric material surfaces is caused by the energy dissipated by mechanical instabilities that take place at the small-scale due to adhesion and surface roughness. The hypothesis will be investigated by studying a model family of continuum mechanics-based contact problems. Equations that connect the mean transverse contact force to the net normal contact force, adhesion and roughness parameters will be derived. By performing an asymptotic analysis of these equations it will be determined whether the mean transverse force remains finite, that is, whether friction type behavior emerges at the large-scale, as the roughness length scale in the problem is made infinitesimally small. New adhesive contact simulation techniques and experiments will be developed and used to guide and verify the theoretical work. Currently, surface mechanical phenomena, such as friction, are considered intrinsic properties and are described with phenomenological models. There is a very limited understanding of how surface phenomena are connected to small-scale mechanisms and parameters. The project aims to derive a micro-mechanics based, mathematical theory of friction. It will lead to fundamental advances required for creating a general, theoretical methodology for understanding how surface properties emerge at the large-scale as the smeared out effects of complex interactions that are hidden at the small-scale.
