Effect of tensile speed on mechanical characteristics of preliminary rolled polyethylene terephthalate films

The effect of tensile speed on the mechanical properties of amorphous polyethylene terephthalate films is studied. The films are oriented by rolling on laboratory rollers at room temperature. In the samples with the rolling degree of two, the subsequent tension with the velocity of 5 mm/min does not afford a neck. As the tensile speed increases to 500 mm/min, a neck results from instability of the deformation process, which is caused by the polymer heating. Upon high-speed tension, the temperature of the rolled samples exceeds the glass-transition point of polyethylene terephthalate. Despite the polymer heating, the rolling completely suppresses the formation of pores. The rolling leads to the delocalization of flow over the region of polymer transfer to the neck. While in the nonrolled films the flow occurs in the zone with the length on the order of the film thickness, after the rolling, the size of the flow zone increases, and the region with the length on the order of the film width is deformed.