Plastic deformation of oriented polyethylene

• Main Author: Simpson, Leslie Ainsley
• Published: University of Surrey 1972
• Subjects: 530.412
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.472746

Tensile test specimens were cut from high density polyethylene sheet that had been fully cold drawn. The angle (lambdao) between the tensile axis and the initial draw direction was varied from 0° to 90° and the specimens deformed between the temperatures of -10°C and 120°C. With the aid of a dot printing technique, analysis of the macroscopic strains revealed an approximate simple shear process, for specimens with angles of less than 90° and greater than 0°. Deviation from simple shear, which was accounted for in terms of a shear reorientation model, was found to be approximately independent of lambdao, although temperature sensitive. It is shown that the shear process beyond yield can be described in terms of a flow criterion, the parameters of which were dependent upon lambdao and temperature. The elastic and pre-yield deformation behaviour for specimens with angles between 70° and 30° was investigated at 22°C, and it appeared that the onset of the flow criterion occurred before the yield point (load maxima) at a critical shear strain. Specimen deformation was also analysed in terms of the relationship between resolved shear stress and shear strain, and this was found to be independent of lambdao. Changes in the morphology during redrawing were revealed by using a combination of wide and low angle X-ray diffraction techniques together with macroscopic strain measurements. Assuming a principle of superposition of shear strains, two modes of slip parallel to the oriented chain axis, intracrystalline slip and fibrillar slip, were postulated in order to account for the observed macroscopic shear strain. It was found that both modes were temperature sensitive.