Bergstroem Boyce Model - inelastic part

Hi, 

 I was wondering if anyone has experience in implementing the Bergstroem-Boyce Model (Constitutive modeling of the time-dependent and cyclic loading of elastimers and application to soft biological tissue, 2001)? I am struggling with the implementation of the viscoplastic part (Network B) of the model:

I’m not really sure at the moment how to implement the stress.  I
understand that you can decompose the deformation gradient F into an elastic and
plastic component.  In the stress formulation they use the elastic part  of F (Eq 2)
to get dev(Be*) and Je.  From all these equations I am not sure how to get Fe
and Fp.  I tried to go backward starting with the effective strain rate (Eq 3).
 However, the rate uses the plastic effective stretch, which is based on the
plastic Bp*, which in term comes from Fp… I understand that the effective strain
rate is an important part of these kinds of models.  

Basically the only thing
known at the beginning of the step is F=FA=FB=Fe=Fp=1.  I’ve tried to find
references/books that explain similar procedures, but couldn’t. 

 Is anyone aware of a describtion of the implementation of a this or a similar model?

 Thanks,

Andreas