The initiation of frictional sliding between a flat-bottomed indenter and a planar monocrystalline substrate was analyzed by using discrete dislocation dynamics. Plastic deformation was modeled by the motion of edge dislocations in an elastic solid. The lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and dislocation annihilation were incorporated via a set of constitutive rules. Adhesion between the indenter and the substrate was modeled by using a shear traction versus sliding displacement cohesive relationship. Two cohesive relationships were used. In both of them, the shear traction increased to a maximum value. In one relationship, the shear traction then decayed to zero with increasing sliding while, in the other relationship, the shear traction remained at its maximum value. The predictions which were obtained by using these 2 cohesive relationships did not differ qualitatively, and the quantitative differences were small. The shear stress which was required to initiate sliding was a function of the contact size. At large contacts, sliding was initiated at a value which was approximately equal to the tensile yield strength. At small contacts, sliding was initiated at the cohesive strength. The effects of a superposed normal pressure on the contact, of the cohesive strength and of the dislocation-source density were also investigated.

Discrete Dislocation Plasticity Analysis of Static Friction. V.S.Deshpande, A.Needleman, E.Van der Giessen: Acta Materialia, 2004, 52[10], 3135-49