Anisotropy, elastic stresses, and yielding

Hook and Hirth first showed how elastic anisotropy can produce local stress concentrations at grain boundaries.4 Consider a single crystal under a compressive stress, crystal A in Figure la. The crystal is so oriented that it will shear in the direction indicated by the arrow. If the crystal is rotated 180 degrees about the vertical axis (crystal B, Figure 1a), the direction of shear is reversed.