Peierls Stress for Screw Dislocations in Polyethylene

Abstract

The Peierls stress for the motion of screw dislocations with [001] Burgers vectors in orthorhombic polyethylene has been investigated. Assumptions made are that a polymer chain moves along [001] as a unit and no intramolecular interactions need be considered, that the chains do not twist during dislocation motion, and that material displacements around the dislocation are the same as in continuum anisotropic theory. The force between chains is shown to vary nearly sinusoidally with relative displacement along the chain direction. The shear moduli C₄₄ and C₅₅ are derived. The Peierls stresses are expressed relative to C₅₅. The results show that for reasonable values of C₄₄/C₅₅, the Peierls stress for screw dislocation glide on a (100) slip plane is about 5×10⁻⁵ C₅₅, while the Peierls stress for dislocation glide on a (010) slip plane is about 0.1 C₅₅. For screw dislocation glide, it is concluded that dislocation motion on a (100) slip plane is probable, but that dislocation motion on a (010) slip plane is highly unlikely. Any slip plane other than (100) for these screw dislocations would necessitate crossing (100) planes, and Peierls stresses arising from glide on (010) slip planes would then be felt. Hence it is concluded that (100) is the only likely slip plane for the glide of such screw dislocations.