NON-SCHMID EFFECTS AND LOCALIZED PLASTIC-FLOW IN INTERMETALLIC ALLOYS

A general strain rate dependent crystallographic slip theory which inc orporates both non-Schmid effects and thermal deformation is presented . The theory is applied to the description of deformation in intermeta llic alloys such as Ni3Al. For Ni3Al, as an example, it is shown that the approach embodies descriptions of stress state dependent yielding as observed experimentally as well as described by existing models suc h as that of Paidar, Pope and Vitek (Acta Metall., 32 (1984) 435). Fin ite element calculations of crystals deforming on only one slip system demonstrate that Asaro and Rice's (J. Mech. Phys. Solids, 25 (1977) 3 09) criterion for bifurcation is a necessary condition for the formati on of shear bands in crystals undergoing slip on only one slip system. Geometric effects are shown, however, to play an important role in th e development of such localized shear bands. Strain rate sensitivity c an delay significantly the formation of the localization, and lattice rotations relative to the surrounding lattice inside the shear bands a re found to be quite small. This is in contrast to the case in multipl e slip where lattice rotations play an important role in the localizat ion process. In multiple slip the criteria for localized plastic flow are found to be of the sort described by Asaro (Acta Metall., 27 (1979 ) 445; Mech. Mater. 4 (1985) 343), although localization generally occ urs much sooner in the deformation process as a result of deviations f rom Schmid's rule.