Micromechanically based formulation of the cooperative model for the yield behavior of semi-crystalline polymers

In this paper, a micromechanically based formulation of the cooperative model is proposed for the yield behavior of semi-crystalline polymers. The semi-crystalline polymer is considered as a two-phase material where the yield processes involved in the amorphous phase and in the crystalline phase are considered separately. By using homogenization methods, the yield behavior of polyethylene and poly(ethylene terephthalate) has been modeled. The Takayanagi model is used to compute an effective activation volume and an effective activation energy which is then implemented in the cooperative model. The predicted results are in good agreement with the experimental results of Truss et al. [Truss RW, Clarke PL, Duckett RA, Ward IM. Polym Phys Ed 1984;22:191] for polyethylene over the temperature range −30–85 °C, and of Lim et al. [Lim JY, Donahue HJ, Kim SY. Macromol Chem Phys 2003;204:653] for the poly(ethylene terephthalate) over the temperature range 20–125 °C.