Effect of Indenter-Radius Size on Au(001) Nanoindentation

We address the question of whether results obtained for small indenters scale to indenter sizes in the experimental range. The quasicontinuum method is used in order to extend the computational cell size to $2\times 2\times 1\mu {\mathrm{m}}^3$, nominally containing of order $2.5\times {10}^{11}$ atoms, and in order to permit consideration of indenter radii in the range $70-700\mathrm{\AA }$. The dislocation structures for the large indenter are found to be less sharp and to extend over a larger region than for the small indenter. In addition, the large-indenter force-displacement curve differs from that corresponding to the small indenter in one important respect, namely, the absence of force drops during indentation, despite profuse dislocation activity. Based on these observations, we conclude that the indenter force is not a reliable indicator of the onset of dislocation activity and plastic deformation for indenter sizes in the experimental range.