Computer simulation of nanoindentation into polymer films

We present computer simulations of nanoindentation into amorphous polymer films. The bulk polymer is treated through a united atom model in connection with molecular dynamics methods. The dynamics of the indenter is modeled as overdamped, such that the indentation velocity is proportional to the difference between the external force acting onto the tool and the resistance force built up in the polymer film. We concentrate on the initial, kinetic stage of the indentation process and give results for the motion of the indenter, the deformation field of the polymer film, the stress field, and the field of total monomer energy. We propose an effective coefficient as a new measure for the resistivity of a surface against indentation. Its value can be determined in an experiment with constant indentation velocity. In addition, we investigate the free drift behavior when the external driving force has been set to zero and the tool is expelled from the polymer film. For different polymer chain lengths, the tool’s motion is exponential in time and we determine the relaxation scale.