Indenter Size Effect on the Reversible Incipient Plasticity of Al (001) Surface Studied via Quasicontinuum Simulations

Indenter size effect on the reversible incipient plasticity of Al (001) surface is studied by quasicontinuum simulations. Two cylindrical indenters with the radii 2.5nm and 17.5nm are used to penetrate the surface respectively, in displacement-control in steps of 0.02 nm. Results show that the plasticity under the small indenter is reversible, since it is dominated by the nucleation of a thin deformation twin, which can be fully removed after withdrawal of the indenter, due to the imaging force and stacking fault energy. Under the large indenter, multiple slip systems are activated simultaneously when incipient plasticity occurs, a few twin, dislocation and stacking fault ribbons still remain under the surface when the indenter has been completely retracted, thus the plasticity is irreversible.