The effect of glass transition on the self-oscillation regime of tensile drawing of a polymer

The effect of the transition of a polymer into its rubbery state at the glass-transition temperature on the character of the excitation of self-oscillation neck propagation is studied with numerical methods. To describe the rate of plastic yielding near the glass-transition temperature, the Eyring equation is modified by the introduction of the temperature dependence of the parameter related to the free volume. There are three intervals of strain rates. At low strain rates when the yield stress increases with an increase in the strain rate, neck propagation is stable and no oscillations are excited. At high strain rates, when the glass-transition temperature is achieved during stationary neck propagation, the excitation of oscillations shows a mild character and there exists a certain critical length of the samples below which no oscillations are excited. In the intermediate interval of strain rates, the excitation shows a severe character. In this case, the oscillations are excited when, in the transition region, the glass-transition temperature of the polymer is achieved owing to excitations. In strain-rate-sample-length coordinates, the diagram describing the regions of various oscillation behaviors of the samples is constructed.