A theory for the low-temperature plastic deformation of glassy polymers

Abstract

Abstract A theory of yielding of glassy polymers by thermally-activated production of local molecular kinks is described. It is possible to obtain the activation free enthalpy of this process by modeling the intermolecular energy barrier as resulting from the stress fields of two equal and opposite closely spaced wedge disclination loops extending over the molecular cross section at the points of rotation of the molecular kinks. The theory predicts the yield stress at absolute zero to be dependent only on the shear modulus and the Poisson's ratio, and is capable of describing the temperature, pressure, and strain rate dependences of the flow stress from absolute zero to near the glass transition temperature. Comparison of the theory with the available experimental, results on polystyrene, polyethylene-terephthalate, polycarbonate of bisphenol A, and poly-methyl-methacrylate shows excellent agreement in nearly all respects.