Effect of Surface Roughness on Nanocontact: Quasicontinuum Simulation

By using the two-dimensional quasi-continuum method, the nano-contact between Ni indenter and single crystal Cu substrate with a smooth or rough surface is simulated. The contact force varies in a nonlinear fashion with the increasing indenter displacement, which includs several force drops. The atomic-scale deformation mechanism in the Cu substrate during nano-contact process is monitored. Shockley partials, Lomer-Cottrel locks as well as twinning faults are observed at the force drops. The Lomer-Cottrel locks play an important role in smooth surface nano-contact process, and they insure that Cu substrate undergoes elastic deformation dominantly during nano-contact process. The contact forces calculated from the Maugis-Dugale (M-D) theory show a good agreement with those obtained by the QC simulation in the smooth surface nano-contact process. It must be noted that the M-D theory is no longer suitable to describe the rough surface nano-contact problem due to the severe plastic deformation in the asperities of the substrate when the characteristic size of roughness is on the order of the indenter depth.