Viscoelastic behavior -prony parameters vs volume data specification

[FSOL]

I have tried to simulate viscoelastic behavior in Abaqus by using volume data from creep expirements. Abaqus then determines the prony parameters and wirte them in the dat file. I tried using these data instead of the volumetric ones. However, the deformation was completely different for the two cases. So i believe that Abaqus uses the volume data for something more than just determining the pronye parameters. Does anyone know what is going on in Abaqus when using these volume data?