Physical aging nonlinear behavior

In the solid state deformation, the nonlinear viscoelastic effect is most clearly shown in the yield behavior. The activation volume tensor is a key parameter. In addition to the well known dependence of yield stress on temperature and strain rate, the functional relationships between yield, stress field, and physical aging are presented. 

The C-F model has been extensively used to compare the aging behavior of polymer blends to that of the corresponding homopolymers, because of its simplicity. However, it should be noted that this model does not adequately describe all of the phenomenology associated with the glass transition, namely, its nonlinear character. The consequences of this when describing the physical aging process have been recently discussed in the literature (Li and Simon 2006 Hutchinson and Kumar 2002). 

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