A numerical study on pile-up in nanoindentation creep

In this paper, we simulate materials of variable hardness, work hardening exponent, χ = ∂1nσ/∂1nε of 0.1?0.3 and a strain rate sensitivity of von Mises stress, vσ = ∂1nσ/∂1nε of 0.08?0.16 to estimate pile-ups and sink-ins during indentation creep and compare the results with literature data. We report that materials pile-up for vΗ/vσ ≥ 1.0 and sink-in for vΗ/vσ < 1.0, vσ is the strain rate sensitivity of the hardness. vΗ/vσ approaches 1 for small Η/Ε*, i.e., soft materials and deformation is dominated by pile-up, whereas when vΗ/vσ approaches 0 for large Η/Ε* corresponds to purely elastic deformation which is apparently dominated by sink-in in a manner prescribed by Hertzian contact mechanics.