Research on the yield limits and slip directions of the twin-shear unified yield criterion

Two aspects of the yield limits and the slip directions for materials in the twin-shear unified yield criterion are analyzed in this paper. The results show that on the yield limits of the materials, the criterion can express the influences of the intermediate principal stress on promoting the values of yield limits and such promotions varied in intervals with the intermediate principal stress. But on the slip directions for materials when yielding, although the effects of the intermediate principal stress can also be characterized in this criterion, the double slip angles are existed when the actual stress states acting on materials meet with the boundary restrictions of the two equations in the twin-shear unified yield criterion simultaneously. Such stress states make the slip directions varied abruptly. So it is summarized that the twin-shear unified yield criterion could not give a proper descriptions to the slip characteristics for the materials when yielding.