Within the framework of the theory of representation, generalizations to anisotropic conditions of the invariants of the deviatoric stress are proposed. Using these generalized invariants, any isotropic yield criterion can be extended such as to describe any type of material symmetry. In this paper, we apply this method to extend to orthotropy Drucker's isotropic criterion. Comparison with data on aluminum alloys show that this new criterion describes with improved accuracy the anisotropy of the plastic response.
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