A simple phenomenological approach to nanoindentation creep

Nanoindentation is frequently used to measure elastic modulus and hardness of structural materials such as ceramics, metals and thin films. The assumption behind conventional nanoindentation analysis methods, where the unloading data is analysed, is that the material behaves in an elastic-plastic manner. However, many materials can also exhibit a visco-elastic and visco-plastic response which is commonly termed “creep”. In a nanoindentation test, this is usually observed as an increase in depth during a hold period at maximum load in the load-displacement data. Creep is not accommodated in conventional nanoindentation analysis methods. The present work shows how conventional linear spring and dashpot elements can be used to model the creep response of a wide range of materials using the hold period force-displacement data. The method shown can be readily incorporated into a computer program and can be used with any conventional nanoindentation test instrument using either spherical or sharp indenters.