Effect of viscoplastic material parameters on polymer indentation

The effect of material parameters characterizing viscoplastic flow on the indentation response of polymers is investigated using three-dimensional finite element analyses and a one-dimensional expanding spherical cavity model. The polymer is characterized by a finite strain elastic–viscoplastic constitutive relation and two indenter shapes are considered; a conical indenter and a pyramidal indenter.

The ability of the simpler expanding spherical cavity model to reproduce the trends obtained from the finite element solutions is assessed for both indenter shapes. Within the range of parameter variations considered, it is found that two material stress parameters characterizing the plastic flow resistance have the largest effect on the value of the indentation hardness although variations in other material parameters can lead to significant variations.