Non-linear generalized elasticity of icosahedral quasicrystals
  Quasicrystals can carry, in addition to the classical phonon displacement field, a phason displacement field, which requires a generalized theory of elasticity. In this paper, the third-order strain invariants (including phason strain) of icosahedral quasicrystals are determined. They are connected with 20 independent third-order elastic constants. By means of non-linear elasticity, phason strains with icosahedral irreducible Gamma^4-symmetry can be obtained by phonon stress, which is impossible in linear elasticity. 
M. Ricker, H.-R. Trebin