  We report a method for describing plasticity in a broad class of amorphous
materials. The method is based on nonlinear (geometric) deformation theory
allowing the separation of the plastic deformation from the general deformation
tensor. This separation allows an adequate pattern of thermodynamical phenomena
for plastic deformations in polymers to be constructed. A parameter describing
the stress relaxation rate of the material is introduced within the frame of
this approach. Additionally, several experimental configurations to measure
this parameter are discussed.
