nonlinear viscoelasticity

In this paper we revisit the mathematical foundations of nonlinear viscoelasticity. We study the underlying geometry of viscoelastic deformations, and in particular, the intermediate configuration. Starting from the multiplicative decomposition of deformation gradient into elastic and viscous parts F=FeFv, we point out that Fv can be either a material tensor (Fe is a two-point tensor) or a two-point tensor (Fe is a spatial tensor).

A research paper published in Vol. 83 of Journal of Applied Mechanics

http://appliedmechanics.asmedigitalcollection.asme.org/article.aspx?arti...

Abstract

  I have written a Fortran code for nonlinear viscoelasticity according to the Hughes' recurrence algorithm based on a total Lagrangian formulation.  And a relaxation test is made. There is some deviation from the analytical solution(Theoretically the stress response should be an exponential decay plus a constant, isn't it?). The numerical ultimate stress is larger than the analytical one. As a larger initial strain is applied, the deviation is smaller. For a inital strain of 10%, there is almost no difference between the num. and analy. solution. What can account for this?