Parameter re-identification in nanoindentation problems of viscoelastic polymer layers: Small deformation

Abstract

Recently, nanoindentation became a new but all the same a primary testing technique of thin layers. A wide application of nanoindentation in polymeric layers is obstructed by the analysis method, which is used to extract the rate-dependent properties. In the present paper, the inverse method based on the finite element simulation and numerical optimisation is used to characterise the viscoelastic properties of polymers from nanoindentation. First of all, the boundary value problems using nanoindentation of polymer layers considering real geometry, is simulated with the FE code ABAQUS®. A linear viscoelastic model for small strain, based on a general Maxwell rheological model is currently applied to describe the rate-dependent material behaviour. The rate-dependent properties of the polymer layer under nanoindentation is investigated with various loading histories: cyclic testing, single step relaxation, monotonic testing, and sinusoidal oscillatory testing. A parameter re-identification strategy offers a deep insight into the relationship between the accuracy of identification and the loading history associated with the rate-dependent material model. A method to choose a suitable loading history to identify the parameters more accurately is recommended. In the present paper, the inverse method based on the finite element simulation and numerical optimisation is used to characterise the viscoelastic properties of polymers from nanoindentation. First of all, the boundary value problem of nanoindentation considering real geometry, is simulated with the FE code ABAQUS®. A linear viscoelastic model for small strains is currently applied to describe the rate-dependent material behaviour. The rate-dependent properties of the polymer layer under nanoindentation is investigated with various loading histories: cyclic testing, single step relaxation, monotonic testing and sinusoidal oscillatory testing. A parameter re-identification strategy offers a deep insight into the relationship between the accuracy of identification and the loading history. A method to choose a suitable loading history to identify the parameters more accurately is recommended. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.