Anisotropy of fracture in hexagonal metals

When plastic deformation in hexagonal metals with lower symmetry than in cubic metals cannot support the external load, the crystal can break along a certain plane. Using a simple criterion based on the surface energy, Young modulus and interplanar separation, the anisotropy of fracture is discussed for three typical hexagonal metals, magnesium, titanium and zinc. The obtained results are generally in agreement with the experimental observations.