Rapid mechanical deformation of poly(ethylene terephthalate) fibers at temperatures above the glass transition

The mechanical properties of poly(ethylene terephthalate) (PET) fibers at temperatures above the glass transition are investigated by means of a specially constructed device. Measurements of the deformation rate and of the “dynamic” stress‐strain curves of the fibers are performed in nearly isothermal regime (after initial rapid heating) in a temperature interval 100–200°C. The results reported in the present work demonstrate that the high‐temperature mechanical characteristics of rapidly crystallizing polymers can be deduced to a satisfactory precision, while keeping the crystallinity development at low level. Our investigations indicate that if the high‐temperature deformation is sufficiently fast, the polymer behavior is similar to the deformation at sub‐Tg temperatures. Based on this similarity, a qualitative model of the deformation in the high‐temperature region is proposed. The proposed model is fundamentally equivalent to the models describing mechanical deformation of glassy polymers at temperatures below the glass transition.