A micro-mechanical dislocation model of contact-induced deformation of a surface step or ledge was offered for the study of meso-scale plastic deformation near to, and at, a rough surface. The onset of contact-induced surface yielding, controlled by single-dislocation nucleation from a surface step, was considered here. The Stroh formalism of anisotropic elasticity, and conservation integrals, were used to evaluate the driving force acting on the dislocation. This driving force, together with a dislocation nucleation criterion, was used to construct a contact-strength map of a surface step in terms of contact pressure, step-height, surface adhesion and lattice resistance. Atomistic simulations of atomic surface-step indentation on a Au(100) surface were also carried out using the embedded atom method. As predicted by the continuum dislocation model, the atomistic simulations also indicated that surface adhesion played an important role in dislocation nucleation. Instabilities due to adhesion and dislocation nucleation were revealed. The atomistic simulation was used to calibrate the continuum dislocation nucleation criterion, while continuum dislocation modeling reflected the dislocation energetics in the inhomogeneous stress-field of the surface-step under contact loading. The results showed that dislocations could be easily nucleated on certain slip planes, but remained in equilibrium positions which were very close to the surface step. The dislocations in some other slip planes easily moved away from the surface and into the bulk. This phenomenon was termed contact-induced near-surface dislocation segregation. The existence of a thin tensile-stress sub-layer, adjacent to the surface and within the boundary layer of near-surface plastic deformation, was predicted.

Micro-Plasticity of Surface Steps under Adhesive Contact - Part I - Surface Yielding Controlled by Single-Dislocation Nucleation. H.H.Yu, P.Shrotriya, Y.F.Gao, K.S.Kim: Journal of the Mechanics and Physics of Solids, 2007, 55[3], 489-516