Tests were conducted at Univ. Bourgogne Franche-Comte, FEMTO-ST Institute, Department of Applied Mechanics, Besancon, France. The tests were conducted under isothermal conditions at room temperature when the frequency of 5 Hz and stress ratio of 0.5 were applied (for a PC -polymer). The elongation of dumbbell -shaped PC-specimens versus the applied force F was measured. The elongation was measured by an extensometer. The stress was defined by F/A, where the area of the initial cross section (gauge section) is given by A. Hysteresis loops given in the paper are based on this stress vs strain -data.