Structure Change and Voids Creation at the Neck of Polyethylene Cylindrical Rod under the Tension-torsion Combined Stress

Abstract

The neck structure formed in polyethylene cylindrical rods under a tension-torsion combined stress was analyzed using wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC). The volume change of microvoids in the neck was investigated suing DSC and density measurements.At the start of a neck, the crystal a-axis is oriented in the direction that is different from the equatorial direction. At the end of the neck, a fibrillar structure is formed. Bundles of fibers are oriented in the direction that is different from the axial direction due to the resultant force of the combined tensile and shear forces, which result sin a spiral orientation of the polymer chains. Microvoids are created during the plastic deformation as a fibrillar structure is formed. However, the volume of microvoids is reduced in the cold drawing region. As a result, it is suggested that the volume of microvoids created among the bundles of fibers is reduced with further twisting.