Dynamical expansion of a dislocation loop on a two-dimensional periodic potential

The equilibrium shape and the motion of a dislocation loop on two-dimensional periodic potential fields are discussed. The Peierls stress for a straight dislocation along non-close-packed direction as well as the Peierls stress for kink migration can be neglected in comparison with that for a dislocation along close-packed directions, provided that the potential is not high. A dislocation loop can take various stable configurations under an applied stress below a certain critical stress. If the dynamic effect of the motion of a loop is taken into account, the segments along non-close-packed directions which start to move under small stresses gain kinetic energy, and the motion of the segments along close-packed direction is induced. Therefore, reduction in the stress for the infinite expansion of a loop can occur.