Computer simulation of polyethylene crystals

Abstract

A simulation by computer of dislocations in orthorhombic polyethylene has been undertaken using the DEVILS suite of programs described in Part 1 [2]. The perfect dis locations with the shortest Burgers vector b have been considered, namely the screw withb=[001] and the edges withb = [010], [100] and 〈110〉. The 〈110〉 edge dissociates into Shockley partials with a very wide spacing and could not be modelled successfully with the crystal sizes employed. The other dislocations have narrow cores, and the [001] screw is symmetrical except for small molecular rotations along the (100) plane. Under applied shear strain, the screw glides on (100), (010) and {110}, with the [001] (100) system having the lowest Peierls stress. The [100] and [010] edge dislocations are not glissile on their slip planes, however. Instead of gliding on (010), the [100] edge dissociates under stress in a non-planar way on the {110} planes. It is predicted that transverse slip in polyethylene occurs by combinations of partial dislocation glide on the two {110} planes.