To take into account the significance of activation volumes, Fotheringham and Cherry have introduced the concept that yielding involves a cooperative motion of polymer chain segments [1]. According to the strain rate-temperature superposition principle [2], a recent development [3] has shown that this type of models can give outstanding results for the determination of the yield stress at high strain rates, as well as above the glass transition temperature. Many phenomena associated with plastic deformation are considered, among these are: the temperature and the strain rate dependence of the yield stress, the correlation with physical processes (beta-transition) and the distinction between the effective and internal stresses. The stress-strain response of the polymer is obtained by implementing the cooperative model in the formalism of the large deformations of solid polymers developed by Boyce, Parks and Argon [4]. Instead of using the Argon model [5] for the plastic flow rule, our proposed new form of the cooperative model is used. The numerical simulations were performed under adiabatic conditions for the polycarbonate and the polymethylmethacrylate for a large range of strain rates and temperatures.
[1] Fotheringham D, Cherry BW. J Mater Sci 1976;11:1368. [2] Bauwens-Crowet C, Bauwens JC, Homès G. J Polym Sci A2 1969;7:735. [3] Richeton J, Ahzi A, Daridon L, Rémond Y. to be submitted to Macromolecules [4] Boyce MC, Parks DM, Argon AS. Mech. Mater 1988;7:15. [5] Argon AS. Phil Mag 1973;28:839.
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