A thermodynamic analysis of Argon's yield stress model: Extended influence of strain rate and temperature

In amorphous polymers, the yield stress is strongly dependent on strain rate and temperature. It is demonstrated that the influence of strain rate and temperature can be studied from a thermodynamic point of view by defining activation parameters. These parameters allow for understanding the mechanisms that take place during plastic yielding. A comparative study based on this thermodynamic framework is conducted on the classical Argon's model for the yield stress. Different cases are investigated using different expressions of the elastic modulus as a parameter of this model: constant Young's modulus value, temperature dependent Young's modulus and temperature-and-strain-rate dependent Young's modulus. The corresponding activation parameters are derived and analysed for a wide range of temperatures and strain rates. The numerical predictions are also compared with experimental data taken from the literature. This analysis shows that the validity of Argon's model can be extended to dynamic strain rates and to higher temperature (up to the glass transition) when combined with appropriate models for the elastic modulus for these ranges of strain rates and temperatures.