Size Effects in Nanoindentation of Hard and Soft Surfaces

摘要

Nanoindentation experiments carried out with atomic force microscopes open the way to understand size-related mechanical effects that are not present at macro- or micro-scale. The shape and behaviour of the nanoindenter AFM tip is however crucial for a correct data analysis and it is currently the subject of a wide and open debate. We have recently developed a simple geometrical model to properly described the tip effect on the nanoindentation process. Here, we demonstrate that this model is valid for both soft and hard or relatively hard materials. Experiments on soft materials surfaces (PolyMethylMetaAcrylate PMMA, PolyStyrene PS) and hard or relatively hard (Si, Au, Al) surfaces are reported. By properly describing the tip geometry and by taking into account effects associated with material displacement during the indentation, we find that plastic and elastic effects can be investigated in truly nanosized indentations. Reliable discrimination between size effects inherent to the material properties and those associated with the instrumental methods is made.