A tension-torsion combined stress was loaded onto cylindrical rods of polyethylene to investigate the deformation mechanism of the crystalline phase under non-uniform stress. On applying the combined stress, a neck occurred at the centre of the sample and extended in the axial direction. After necking occurred, the twist deformation generated compressive stress in the radial direction, which suppressed the formation of micro-voids. Wide-angle X-ray diffraction revealed the following facts. The c axis, i.e. the crystal molecular chain axis, deviates from the axial direction owing to the combined loading of the tensile force and the shear force. The b axis, which is the long axis of the initial lamellae, orients selectively in the radial direction in the non-uniform stress state in which the shear stress increases in proportion to the distance from the centre of the cylindrical rod.
Посилання на статтю:
Orientation behaviour of crystallites in cylindrical polyethylene rods under tension-torsion combined stress / Takeshi Katagiri, Masanobu Sugimoto, Eiji Nakanishi* and Sadao Hibi // Polymer. – 1993. – Vol 34. – P. 487-493.