Anisotropic elasticity

Summary

Anisotropic elasticity is linear elasticity for materials whose elastic response depends on direction. The elasticity tensor of such a material is not invariant under all rotations. It can have up to $21$ independent constants instead of the $2$ of an isotropic material. Crystals, wood, fibre composites and rolled metals are anisotropic, so the theory is needed for most engineering materials with a structure.