Equilibrium and passing properties of dislocation dipoles

Abstract

Static and dynamic properties of dislocation dipoles are investigated under isotropic and anisotropic elasticity. In elastically isotropic systems for a dislocation character between 35 and 40°, a dipole assumes the same stress-free equilibrium angle of 90° as the screw dipole. This can be affected by elastic anisotropy, as in Cu where the equilibrium angle assumed by a screw dipole (≈59°) is unchanged up to a dislocation character of 22°. In contrast, the static properties of near-edge dislocation dipoles are little influenced by elastic anisotropy. Certain dipole passing properties, not the passing stress however, are also modified by elastic anisotropy. For large heights and/or in the case of undissociated dislocations, the minimum passing stress corresponds to a dipole character of ∼60° and it exhibits a sharp maximum in screw orientation. Reasonably moderate dislocation reorientations should facilitate the passing of near-screw dislocations in fatigue channels. Within a certain range of applied stresses, the passing of dipoles, comprised of unlike attractive dislocations, is accompanied by the sweeping of one dislocation by the other over a limited distance. Dissociation plays a prominent role in determining both static and dynamic properties for dipole heights less than a few times the dissociation distance of an isolated dislocation.