On the Effect of Heat Transfer on Self-Oscillating Neck Propagation

The effect of the surroundings on stress and temperature self-oscillations during stretching of polyethylene terephthalate films has been studied. The tests were carried out in air, helium, and sulfur hexafluoride. Spontaneous acceleration of plastic flow is due to the conversion into heat of elastic energy stored by the specimen during stretching. It has been shown that an increase in the thermal conductivity coefficient of the gas leads to an increase in the average stress and oscillation amplitude and a decrease in the oscillation frequency. These changes are explained by an increase in heat transfer and, accordingly, a decrease in the temperature of the polymer flow zone. A decrease in the film thickness leads to an increase in the heat transfer to heat release ratio, which is similar to an increase in the heat transfer coefficient.