It is often crucial to control friction of soft material surfaces. For example, high sliding friction between rubber tires and the road surface enables quick braking. In the biological context, it is sometimes desirable to minimize friction, as between a contact lens and the eye. On other occasions high friction is needed, for example when designing hands of a soft robot for grasping objects. This Leading Engineering for America's Prosperity, Health, and Infrastructure (LEAP-HI) Grant Opportunity for Academic Liaison (GOALI) project will develop two novel mechanisms to improve friction of soft materials based on bio-inspired design of near-surface structures. The research will be carried out by a research team with members from Lehigh and Cornell Universities, and Michelin USA, with application to tires. Tire production is a major component of the US industrial profile. Dozens of plants produce over 150 million car, truck, bus and other tires per year. This research will support innovation that is needed to both increase vehicle safety and help the USA to maintain its position as a leading tire manufacturer.
Friction as an interfacial property is usually understood to be governed by interfacial intermolecular interactions, coupled to bulk deformation and energy dissipation at macroscopic length scales, for example by viscoelasticity. Recent work on bioinspired and biomimetic materials has shown how appropriately designed near-surface structures at a meso-scale (microns) intermediate between the molecular (nm) and continuum scales (mm and larger) can be used to strongly modulate surface properties like adhesion. This has opened up a new paradigm and mechanisms for design of soft material interfaces, which however has been little exploited for control of friction. Some of these mechanisms are meso-scale versions of molecular level phenomena that underlie the fundamental question of how friction arises between surfaces in the first place. The goal of this project is to study and develop two meso-scale mechanisms underlying frictional energy loss, a) Meso-Scale Dislocation Arrays: in which the interface comprises a periodic array of features that accommodate misorientation by generating meso-scale interfacial dislocations, which can be used to control friction, and b) Elastic Hysteresis: in which periodic near-surface patterning of elastic modulus can be used to set up a periodic resisting force that, in turn, sets up mechanical instabilities and hysteresis to yield large friction enhancement.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
