Nonlinear UEL and UMAT

Hi,

I've been learning how to implement material models using UMAT in ABAQUS and I have

some simple questions:

I've been trying to implement the viscoelastic models in the paper:

Formulation and implementation of three-dimensional viscoelasticity at small and finite strains

Kaliske, M.; Rothert, H., Computational Mechanics, Volume 19, Issue 3, pp. 228-239 (1997) .