Nonlinear dynamics and the problem of slip at material interfaces

The problem of dry friction between two metallic interfaces is discussed fr om the perspective of large scale molecular dynamics (MD) simulations. For flat interfaces between identical metals, two-dimensional MD simulations us ing embedded-atom-method potentials for copper have shown a variety of phen omena associated with a velocity weakening of the tangential force at high relative velocities (approaching significant fractions of the transverse so und speed). These include dislocation generation, dislocation motion both p arallel and normal to the sliding interface, large plastic deformation, nuc leation of microstructure, diffusive coarsening of microstructure, and mate rial mixing. The early time behavior of a flat sliding interface is dominat ed by dislocation motion parallel to the interface. For this early stage, l ower-dimensional models are useful in interpreting some of the simulation d ata. A two-chain forced Frenkel-Kontorova model reproduces some of the beha vior of the larger scale simulations when the phenomenological damping is t aken to be consistent with the MD simulations. This model exhibits four vel ocity regimes of steady state flow which will be discussed. Some of the imp lications for the nucleation of microstructure will be addressed. Copyright (C) 1998 Published by Elsevier Science B.V.