Self-Oscillatory Neck Propagation in Polymers

The oscillatory neck propagation during cold drawing of PET was studied. The mechanism of self-oscillations is heat instability of neck propagation. Oscillations are observed at high velocities when the draw stress increases with an increase in cross-head speed. Neck propagation is described by three equations, which were solved numerically. The solution of these equations predicts appearance of oscillations at high elongation velocities in agreement with experimental observations. The necessary condition of appearance of oscillations in any polymer is existence of some interval of cross-head speeds V, where the draw stress decreases with an increase in V. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 654-661, 2011