Macroscopic Anisotropic Properties
10.1. Aniso- and isotropic samples and properties
In order for a given sample to exhibit anisotropic macroscopic properties, two necessary conditions must be fulfilled. The first is that the individual crystallites intrinsically exhibit the anisotropic property concerned. However, in a polycrystalline aggregate, this intrinsic anisotropy of the crystals can be revealed at the macroscopic scale of the specimen only in the presence of texture. We can then distinguish 4 different types of samples:
– randomly oriented specimen with isotropic crystallites (isotropic sample);
– textured specimen with isotropic crystallites (textured isotropic sample);
– randomly oriented specimen with anisotropic crystallites (isotropized sample);
– textured specimen with anisotropic crystallites (anisotropic sample).
Texture is understood here as both morphological and crystallographic textures, since a specimen with randomly oriented crystals, but with anisotropically aligned grain shapes (morphological texture), can still be macroscopically anisotropic, depending on the properties. For example, in an isotropized sample, with a strong morphological texture and in the absence of crystallographic texture, the interaction between neighboring grains can result in mechanically anisotropic properties. The term quasi-isotropic is sometimes used for isotropized samples [WEL 05], but the term “quasi” would leave us to imagine that anisotropy is almost eliminated ...