abaqus indentation viscoelastic

Hello,

I'm trying to model indentation of a viscoelastic material in Abaqus.

I have (1) stress-relaxation curves for the material and (2) force-displacement curves for the material from a real indentation experiment.

From this I can readily calculate the elastic modulus (infinite) and the elastic modulus (instantaneous) for the material.

I'd like to fit a Prony series based on this data that I can enter into Abaqus to model the material.

How would I go about fitting the Prony series from the force-displacement and stress-relaxation curves?