A material is orthotropic if its mechanical properties are unique and independent in the directions of three mutually perpendicular axes. Examples of orthotropic materials are wood, many crystals, and rolled metals.
For example, the mechanical properties of wood at a point are described in the longitudinal, radial, and tangential directions. The longitudinal axis (1) is parallel to the grain (fiber) direction; the radial axis (2) is normal to the growth rings; and the tangential axis (3) is tangent to the growth rings.
