Micro- and Nano-Mechanics of Surface Contact Plasticity

Yanfei Gao, Brown University

Rough surface contact plasticity at microscale and nanoscale is of crucial importance in many new applications and technologies, such as nano-imprinting and nano-welding. The multiscale nature of surface roughness, the structural and size-sensitive material deformation behavior, and the importance of surface forces and other physical interactions give rise to very complex surface phenomena at small scales. We first show the pathological behaviors of contact models based on fractal roughness and continuum plasticity theory. A micromechanical model of surface steps under adhesive contact examines dislocation nucleation from surface sources and dislocation interaction underneath. The dislocation nucleation process is studied by both atomistic simulations and the Rice-Thomson model. Depending on interface adhesion, roughness features and slip planes, we have a variety of surface deformation behaviors, such as anisotropic hardening and latent softening. As a consequence, the rough surface contact at mesoscale leads to the formation of a dislocation double layer, which cannot be predicted by existing continuum and nonlocal plasticity theories. The micromechanical analysis of surface plasticity could serve as the connection between microscale bulk dislocation plasticity and nanoscale atomistic simulations.