A model was proposed which described monocrystalline creep behavior by using evolution equations for the dislocation densities on individual slip systems. An interaction matrix determined the effect of one glide system on another. Upon assuming a face-centered cubic crystal that permitted deformation on octahedral glide planes and cube glide planes, with a Burgers vector of a/2(110), 9 independent parameters of the interaction matrix could be distinguished. An examination of the 9 parameters revealed their effect upon particular orientations of the load axis. If it was assumed that dislocation interaction of a glide system occurred only with itself, a smooth behavior was predicted; with the highest creep rate being found for the [001] orientation, followed by [011] and [111]. If a strong interaction was assumed, the orientation-dependent creep behavior was not at all smooth but instead exhibited a sharp drop in creep rate; mainly for symmetrical positions in the standard orientation triangle. The orientations with the highest creep rates were, in this case, those which favoured single glide. Highly symmetrical orientations, such as [001], [011] and [111] exhibited strongly decreased stationary creep rates.

Material Model Describing the Orientation Dependent Creep Behavior of Single Crystals Based on Dislocation Densities of Slip Systems. H.Brehm. U.Glatzel: International Journal of Plasticity, 1999, 15[3], 285-98