WIT Transactions on Engineering Sciences vol:77 pages:3-15
Materials Characterisation edition:6 location:Siena date:4-6 June 2013
In this study a comparison between the characterisation of material properties on micro and macro scale was made. Spherical indentations were performed at the micro scale while tensile experiments represent the macro scale behaviour. The samples for both types of experiments were made of the same polyurethane elastomer sheet film. The experimental test setups were load controlled and consisted of a loading phase followed by a holding phase in which the material exhibited a creep response under a fixed load. In order to visualise and quantify the occurring strain levels during the indentation experiment, a FE-model was build. Based on the outcome of this FE-model, the macro tensile test setup was established. According to this procedure, the material experienced a similar level of deformation during both types of testing.
As described by M. Oyen (J. Mater Res., 20, 2094-2100, 2005) the standard linear solid model was applied to capture the material behaviour during indentation testing. The model was adapted for macro tensile testing and applied to fit the experimental data. This fitting procedure was executed through the use of different scripts and revealed quantitative values for all components (spring and time constants) of the standard linear solid model.
The dependence of the results on different loading rates and hold values was investigated. The results of these experiments indicate an overall stiffer response of the material during the nanoindentation tests compared to the macro tensile tests. This observation can be explained by the obstruction of the poisson effect during the indentation test. An extra boundary condition like biaxial tensile tests could be introduced in the future in the macro scale tests. The influence of the loading rate and hold value was minimal and validated the use of a linear viscoelastic analysis.