Creep rupture of a linear polyethylene: 1. Rupture and pre-rupture phenomena

The creep rupture behaviour of a high-density polyethylene was studied for material prepared at two different cooling rates. The rupture phenomena were dependent upon the morphology. The slow-cooled specimens had a degenerated spherulitic structure and all underwent brittle rupture. The fast-cooled specimens had a banded spherulitic structure and exhibited either ductile or brittle rupture depending upon the applied stress. Ductile creep rupture was associated with a large tertiary creep strain, with macro-necking and a stress whitening which corresponded to an increase in volumetric strain. Brittle creep rupture was associated with an absence of macro-necking, and either an absence or a small amount of tertiary creep. Stress whitening corresponding to a decrease in volumetric strain was a feature of both forms of failure above a threshold value of stress.