A theory of yielding of amorphous polymers at low temperature — a molecular viewpoint

Abstract

Nearly homogenous elastic shear on a molecular level rather than localized defect motion was considered to be the primary strain mechanism prior to yielding. The greatest or ideal value of the yield point for an amorphous polymer in the absence of the thermal activation was calculated. The theory involves a picture of the molecular motions under a shear stress involving three interconnected processes: 1. Shearons or intermolecular shear, 2. Rotons or intramolecular shear, 3. Tubons or motion along the covalent bond. The shear resistance was based on the stress to overcome the van der Waal's bond using a (6–12) potential. The model assumes that all atoms move co-operatively by the above motions, up to the point of yielding. Temperature was considered only as it affects the modulus, but the theory has not been extended to include thermal activation. The predicted value of shear yield point divided by shear modulus is <0.064 to 0.092; a review of all the experimental data obtained by extrapolations to 0 K gives an average value of 0.076±0.03.