NON-SCHMID YIELD BEHAVIOR IN SINGLE-CRYSTALS

APPARENTLY, certain single crystals do not obey Schmid's law for slip on individual systems. For example, many intermetallic compounds such as Ni3Al with the Ll2 structure display yield behaviors that are called "anomalous" in the sense that the critical resolved shear stress in the primary slip system at yield is a function of the orientation of the loading axis and the sense of load. To accommodate such non-Schmid behaviors, a generalization of Schmid's law is proposed where stress components other than the Schmid stress also enter the criterion. The general effects of "cross slip" in FCC single crystals as well as the detailed shield behavior of Ni3Al are well described. Finally, we demonstrate that non-Schmid effects can make it more difficult to activate many slip systems simultaneously.