Yield stresses Argon model

The macroscopic upper yield stress is lineary related to Tg — T for a given strain rate, and can be adjusted with Argon s, Bowden s, and Kitagawa s models. The influence of strain rate is well represented by the phenomenological Eyring s equation. 

To assemble the sensor, the sandwich in Fig. 3 was compressed in an argon atmosphere at temperatures ranging from 1,250 °C to 1,290 °C in a universal testing machine (Instron, Model 1125) at crosshead speeds of 0.01-0.02 mm/min and a strain rate of 4 x 10 s At temperatures above 1,250 °C, this strain rate is expected to yield a total stress on a 1 cm sample of less than 40 MPa [24]. During the heating cycle, the load on the sample was balanced as not to exceed 5 N. Upon reaching the target temperature, the system was left under a 5 N load for 30 min to attain thermal... 

A final consideration is that the Argon theory essentially regards yield as nucleation controlled, analogous to the stress-activated movement of dislocations in a crystal produced by the applied stress, aided by thermal fluctuations. The application of the Eyring theory, on the other hand, implies that yield is not concerned with the initiation of the deformation process, but only that the application of stress changes the rate of deformation until it equals imposed rate of change of strain. The Eyring approach is consistent with view that the deformation mechanisms are essentially present at zero stress, and are identical to those observed in linear viscoelastic measurements (site model analyses in Section 7.3.1). Here, a very low stress is applied merely to enable detection of the thermally activated process, without modification of the polymer structure. 

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