Influence of Rolling Speed on the Mechanism of Adiabatic Shear Band Formation and Plastic Flow in Polyethylene Terephthalate Films

Amorphous polyethylene terephthalate was oriented by rolling at room temperature on laboratory rollers. During rolling, a system of shear bands appeared, which was observed using crossed polarizers. The effect of rolling speed and degree on the shear band system was studied. At low rolling speeds (6.5 mm/min), plastic flow occurs through numerous fine shear bands. At higher speeds (above 1300 mm/min), a single serrated deformation zone is observed. This is explained by thermal softening of the polymer and a decrease in yield strength, which suppresses the formation of competing shear bands. At intermediate rolling speeds, two, three, four, or five serrated zones appear, spaced approximately equally. Increasing the degree of rolling leads to an increase in the number of serrated shear zones and homogenization of the flow process. The temperature in the shear bands was estimated, and it was shown that very slight heating of the bands is sufficient to prevent the formation of multiple fine shear bands. A significant difference was noted between the adiabatic deformation of the sample and the adiabatic shear bands.