Crystal Elasticity. Pascal Gadaud

      [1.59]

      According to the anisotropy, each one corresponds either to a maximum or a minimum. Therefore, for a rectangular section, for example, the weighting calculation of the directions in the formalism is needed, which additionally requires the knowledge about the orientations of the sides of the rectangle.

      The problem can be solved by measuring Poisson’s ratio or the shear modulus only along the directions of type <100> or <111> in which these two quantities are anisotropic.

As far as the hexagonal symmetry is concerned, the same type of reasoning leads to conducting the measurements of these two quantities only along the direction z in which they are equally isotropic.