High strain rate testing at the nano-scale: A proposed methodology for impact nanoindentation

Hard, brittle materials are often subjected to mechanical loading on the nano-scale at high strain rates, and while high loading rates can be achieved on the macroscopic scale, there are few methods in the micro-mechanical regime in which these materials can be plastically deformed. Impact nanoindentation is a possible method which retains the flexibility of quasi-static nanoindentation, namely that it is useable for a wide range of materials and can be used to test small phases in a site-specific manner while still applying high strain rates. It therefore helps elucidate deformation mechanisms in regimes that were not accessible up to now. However, previous investigations suffered from limitations regarding the data acquisition, subsequently reducing the scope and accuracy of the determined properties. Here, an improved experimental setup is used and a systematic analysis is described which analyses the energy loss, indentation depth recovery and dynamic hardness over a wide range of strain rates. The accuracy of the results is investigated by atomic force and optical microscopy, compared to the accuracy of other approaches and discussed. (C) 2018 Elsevier Ltd. All rights reserved.