| Most metallic alloys and thermoset polymers are
considered isotropic, where by
definition the material properties are independent of direction.
Such materials have only 2 independent variables (i.e. elastic
constants) in their stiffness and compliance matrices, as opposed to
the 21 elastic constants in the general anisotropic
case.
The two elastic constants are usually expressed as the Young's
modulus E and the Poisson's
ratio n. However, the alternative
elastic constants K (bulk
modulus) and/or G (shear
modulus) can also be used. For isotropic materials, G and
K can be found from E and n
by a set of equations,
and vice-versa. | 
