Attempt to correlate the yield processes above and below the glass transition in glassy polymers

This paper is concerned with a model which attempts to describe quantitatively, by the same elementary process, the yield behaviour above and below T_g, as well as the effect of annealing on the yield stress. This model links together theories we have previously proposed and relies on the following main assumptions: the deformation processes imply the cooperation of n activated segments and that the free energy increase of an activated segment depends on the structural state of the polymer. A satisfactory agreement is found with yield stress data on polycarbonate (PC), over a very large range of temperatures and strain rates. The correlation between the yield stress and the annealing treatment is also reasonable.