Lamé parameter

The two Lamé parameters $\lambda$ and $\mu$ determine the linear isotropic relation between stress and strain; $\mu$ is the shear modulus.

An isotropic linear elasticity material with equal positive Lamé parameters has Poisson's ratio $1/4$ and the displayed compressional/shear speed ratio. This simplifying model fixes the relative amplitudes in the tensile-crack radiation pattern; it does not describe every stable isotropic solid.