What does it mean when we say a certain property of a materi

What does it mean when we say a certain property of a material is anisotropic? Explain in the context of the elastic constant of single crystal BCC iron unit cell. Also, in a macro scale sample made out of this single crystal BCC iron, what does it mean?

Solution

anisotropy is the property bhy virtue of which amaterial exhibits different properties in different directions .It is caused by preferred orientation of grains(crystallographic texture).

A single crystal often has distinctive plane faces and some symmetry. The actual shape of the crystal will be determined by the availability of crystallising material, and by interference with other crystals, but the angles between the faces will be characteristic of the material and will define an ideal shape.

Let\'s picture the simplest lattice: BCC iron unit cell. If you are an atom at a corner and look along the edges of the lattice unit cell, your nearest neighbor is one lattice parameter distance away. However, the nearest neighbor when looking in a direction towards the opposite corner of the unit cell will be sqrt(3)/2 times longer, and when looking towards the atom on the adjacent face in the opposite corner will be sqrt(2) times longer. In other words, the linear density of atoms along any given direction varies simply due to the crystal symmetry. Many properties will vary with this linear density, even when all atoms are the same.

macrosample

When a material is formed, the grains are usually distorted and elongated in one or more directions which makes the material anisotropic.