Toward A Sound Understanding of Dislocation Plasticity

Abstract

A novel theory is presented for work hardening in stage II shown by single crystals of ductile face-centered cubic (fcc) metals. The theory is based on the assumption that slipbands are highly elongated ellipsoidal zones with weak interiors, oriented at small, alternating angles with the crystallographic slip planes. Consideration of the stacking of such ellipsoids, together with a condition for the nucleation of a new slipband at the center of an obstacle nearby, yields both the average angle of inclination and the shear offset in the bands, both of which remain constant throughout stage II. The theory makes several predictions concerning the internal stress distribution and the plastic behavior. Before expounding the theory, the concepts upon which it is based are discussed in the context of two much simpler problems: the work hardening of dispersionhardened metals and the cyclic work hardening which forms the basis of understanding fatigue properties. The picture confirms in a natural way that the value of σ _III , the stress which marks the end of stage II hardening, may be taken to be equal to the fatigue endurance limit.