Micro- and Nano-Mechanics of Surface Contact Plasticity

The science-based methodologies we introduce students to first should be those that provide for tackling the broadest possible classes of problems. In this seminar I will review some of the historical antecedents that underlie most of our current undergraduate science-based curricula and then, as an example, introduce a means of introducing basic mechanics in a way that gives students access to a very broad class of problems of professional interest.

As a demonstration that these methods can be used to solve problems of significant professional interest, I will show an application to the dynamics of a spinning satellite with long radial wire appendages.

Rough surface contact plasticity at microscale and nanoscale is of crucial importance in many new applic at ions and technologies, such as nano-imprinting and nano-welding. The multiscale n at ure of surface roughness, the structural and size-sensitive m at erial deform at ion 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 disloc at ion nucle at ion from surface sources and disloc at ion interaction underne at h. The disloc at ion nucle at ion process is studied by both at omistic simul at ions and the Rice-Thomson model. Depending on interface adhesion, roughness fe at ures and slip planes, we have a variety of surface deform at ion behaviors, such as anisotropic hardening and l at ent softening. As a consequence, the rough surface contact at mesoscale leads to the form at ion of a disloc at ion 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 disloc at ion plasticity and nanoscale at omistic simul at ions.