The modelling of large deformations of pre-oriented polyethylene

High temperature reversion tests have revealed a state of pre-existing mole cular orientation in extruded polyethylene sheet. This state is related to differences in stress-deformation behaviour when specimens of the sheet are stretched along different angles with respect to the extrusion direction. An established large deformation, rate-dependent constitutive equation has been developed to model this material, by incorporating the pre-orientation by the addition of a strained Gaussian network. The level of pre-orientati on is deduced from the dimensional changes on shrinkage. The constitutive e quation is incorporated into the finite element package ABAQUS, and the sha pes and drawing forces of tensile specimens extended at various angles to t he extrusion direction are modelled. (C) 2001 Elsevier Science Ltd. All rig hts reserved.