Modelling and parameter re-identification of nanoindentation of soft polymers taking into account effects of surface roughness

In this paper the characterisation of polymers by nanoindentation is investigated numerically by the use of the inverse method. Effects of the surface roughness are explicitly considered. The boundary value problems of the nanoindentation of two polymers, PDMS and silicone rubber, are modelled with the FE code ABAQUS (R). The model parameters are re-identified by using an evolution strategy based on the concept of the numerical optimisation. The surface roughness effects are investigated numerically by explicitly taking into account the roughness profile in the model. At first the surface roughness is chosen to have a simple representation considering only one-level of asperities described by a sine function. The influence of the surface roughness is quantified as a function of the sine parameters as well as of the indentation parameters. Moreover, it is verified that the real surface topography can be characterised by using multi-level or simple one-level of protuberance-on-protuberance sinusoidal roughness strain-energy function. profiles. The effects of the surface roughness are investigated with respect to the force-displacement data and the identified model parameters. These numerical results are expected to offer a deep insight into the influence of the real surface roughness at the results of indentation tests. (c) 2012 Elsevier Ltd. All rights reserved.