An indentation method to determine the constitutive parameters of hyperelastic films under large deformation: Theoretical model, experiments and simulations

The characterization of the mechanical properties of soft films is of great importance for their applications. In our previous research, we demonstrate the existence of a maximum load occurring during the indentation process of a perforated film by a spherical indenter. Based on this result, an approach to obtain the shear modulus of the film material using the method of finite element analysis has been proposed. However, our previous work does not consider the effect of friction between the film and the indenter, which has a significant influence on the value of the maximum load. Here, a theoretical model is presented which takes into account the role of friction. The reliability and accuracy of the theoretical model are validated by comparison with simulations and experimental results. In addition, the indenter eccentricity and round hole shape deviations which commonly occur in actual indentation tests, are investigated by combining indentation test measurements with finite element analysis. The performance of this method on porous films is also analyzed experimentally and numerically. The results reveal that this indentation method is still effective for porous films. This work provides a fundamental understanding of the mechanism of the indentation method and is expected to provide a new perspective for local characterization of films, even with multiple holes.