Counter-Intuitive Stress Relaxation Behavior of Glass Forming Materials and the Ability of Rheologically Simple “Material Clock” Nonlinear Viscoelastic Modeling to Represent it*

The observance of an increase in glassy polymer relaxation rates under a mechanical deformation is often referred to as deformation induced mobility (DIM). It has been argued that stress relaxation experiments can provide indirect evidence of this phenomenon. Recently, stress relaxation experiments have been interpreted as demonstrating a mobility decrease with increased deformation when very slow strain rates, 1.2 x 10^-5 s^-1, are used to apply the deformation. This would suggest against generality of DIM and would have significant implications to constitutive models founded on this principle. Here, we test the proposed interpretation by assessing the situation using an extensively validated, thermorheologically simple, “material clock” model, the Simplified Potential Energy Clock (SPEC) model.