This study is conducted on the two

This study is conducted on the two polymers PP/EPR and PET Fig.1 shows the true mechanical curves ofthese two materials obtained by the Video Traction system intension for three different true strain rates. For both materials, an increase ofstress is observed up to moderate strain levels with increasing the stretching rate. The yield point is higher in the case ofРЕTthan in the case of PP/EPR whatever the studied strain rate. After the yield point, different amplitudes of softening appearbetween these two polymers, since PP/EPR is semi-crystalline and stretched at a temperature higher than its glass temperatures (Tg PP= 10 °Сand Tg EPR = 45 °C) and PET is amorphous and stretched in its glassy state (Tg = 75 °С). Then, plasticitystage is characterized by a quite large plateau. Finally , strain-hardening takes place to large strain level. However, duringthe strain-hardening stage, the stress-strain curves are not parallel anymore for the two materials, as indicated in Fig. 1. Thisphenomenon does not enable to predict the tensile behavior at large strain level using phenomenological constitutive equations as the one proposed by G’sell and Jonas (1979).