Bridging Atom-scale Dissipation and Surfaces Sliding – BADaS2

Friction is a phenomenon that takes root in the many, both in kind and in number, molecular interactions that occur when two surfaces are close enough. However, these interactions are greatly influenced by the roughness of these surfaces, and by the long distance dialog between micro-contact junctions that takes place through the medium of bulk interactions. This distortion of the molecular picture explains in part why macroscopic friction models, like Coulomb friction or the more general rate-and-state friction, remain empirical. Shortcomings of such models lie in lumping together different physical processes that contribute to the macroscopic friction force. For example, frictional aging, the increase of the force needed to slide an interface initially at rest, comes from different mechanisms (e.g. creep and structural aging) which may compete, leading to behavior that cannot be captured by these models. The aim of the proposed research is to develop and deploy a multiscale modeling strategy to make predictions on the interactions between roughness, surface structural properties, and bulk properties that underlie the competition between different sources of frictional aging within polymer glasses. The multiscale framework described in this proposal combines molecular models, which account for the friction behavior of contact junctions at the nanoscale, and continuum models of rough contacts with viscoelastoplastic bulk constitutive behavior, which, using the junction friction knowledge at the atomic level, will help upscale it to the macro-scale, thus combining the structural (glass-like) aging and geometric (viscoelastic) aging mechanisms observed in polymer frictional experiments. While aimed at polymers, this multiscale framework will break ground in a transferable approach to friction. Ultimately, this will impact how surfaces and materials are designed to frictional constraints, leading to better performance and lower energy consumption.