Twinning and martensitic transformations in oriented high-density polyethylene

Abstract

The deformation of high-density polyethylene with a single crystal texture by shear in directions perpendicular to the chain direction has been examined by wide-angle X-ray diffraction. It is found that samples can undergo either a martensitic transformation to a monoclinic cell, (100) [010] slip or (110) twinning depending upon the orientation of the specimen to the compression direction. A specific orientation relationship has been found between the new monoclinic cell and the parent orthorhombic cell and this has been compared with relationships found by other workers. Stress-strain curves have been obtained from other specimens and it is suggested that for specimens in certain orientations yield may take place by means of a martensitic transformation at a critical resolved shear stress of 14 ± 1 MNm-².