THE DUCTILE BRITTLE TRANSITION IN A POLYETHYLENE COPOLYMER

The ductile-brittle transition of an ethylene-hexene copolymer was measured from 80 to 24° C. The basic curves of stress against time to failure could all be unified in terms of a single equation based on normalizing the stress relative to the transition stress between the ductile and brittle regions and using a single thermal activation parameter. This unity is based on the observations which show that the ductile and brittle failure processes are both associated with a shear process. The unifying equation is {Mathematical expression} where σc is the minimum stress for ductile failure at an arbitrary temperature, TR; tR is the time to failure at an arbitrary reference temperature TR; n equals 34 and 3.3 for the ductile and brittle regions, respectively and R is in J mol-1 K-1. © 1990 Chapman and Hall Ltd.