HIGH-SPEED DEFORMATION OF THE POLY(ETHYLENE-TEREPHTHALATE)

Mechanical behaviour of amorphous and semi-crystalline polyethylene te rephthalate films is studied over five decades of strain rates, at tem peratures below and above the glass transition. The data were obtained by combining measurements from conventional Instron machine with data from a high-speed tensile machine. The activation parameters are dete rmined and compared with the activation process of the beta relaxation . Different modes of failure have been identified and the occurrence o f an intermediate mode between ductile and brittle failure is shown. T he brittle-ductile transition is estimated for each testing conditions and compared to the adiabatic-isothermal transition.