Objective stress rate considerations for viscoelastic response of polymers

An important consideration in the analysis of the film cast process is the objectivity of the stress and strain rate. This paper addresses objectivity as it applies to the constitutive description of a visco-elastic material undergoing finite deformations. This paper briefly reviews the notion of objectivity and then goes on to question the practice of replacing strain rate with rate of deformation in order to accommodate finite strains. A more consistent approach is to make use of the same co-rotational rate for stress and strain. This paper also shows that it is not always necessary to explicitly introduce the objective rates when solving problems dealing with large deformations. Taking advantage of this property, an example is provided that demonstrates the value of the updated Lagrangian analysis for studying the film cast process.