SHEAR-BAND POSTBIFURCATION IN ORIENTED COPPER SINGLE-CRYSTALS

By in situ SEM observation performed in oriented copper single crystals strained in tension, the formation and propagation processes of macroscopic shear bands (MSB) as well as the consequences of their interactions are analysed. We found that an MSB consisted of a collection of parallel shear bands on slip lines scale. The observed lengthening and thickening of MSB were related to saturation of the individual shear bands and to nucleation of new ones in the adjacent matrix. In order to understand this phenomenon, a post-bifurcation model is applied to an idealized planar double slip single crystal. We show that shear banding is effectively characterized by the three observed stages: bifurcation, large shear strain localization and saturation. The bifurcation is accompanied by unloading in the matrix. The saturation is due to the fact that the geometrical softening leading to the bifurcation decreases with localized shear.