On the tensile behaviour of oriented polyethylene

Abstract

Tensile tests of oriented, high-density, polyethylene films were carried out in order to assess how far the intrinsic molecular and textural features of the samples affected their mechanical behaviour, and to see whether this behaviour bore any resemblance to that of metals. Brittle fracture, ductile fracture or necking followed by drawing occurred, depending on the pretreatment used to orient the material, the angle between the tensile axis and the c axis, and the speed of testing. The feature of the crystalline texture (common to all the films) which was important in determining the geometry of deformation was the alignment of the c axis; the additional orientations present in some of the films did not significantly affect the deformation geometry. The results suggested that ductile deformation approximated to slip in the direction of the c axis, while brittle fracture was observed to occur on planes parallel to the c axis. There were some noticeable differences in behaviour between those films which had received a pre-anneal and those which had not; these differences appeared not to be due to differences in the crystalline texture. Several striking similarities to the mechanical behaviour of hexagonal single crystals were observed.