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The development of improved ductile damage models for plastically anisotropic
materials has received limited attention in the literature. We derive a new
yield criterion for materials containing spheroidal voids embedded in a Hilltype
orthotropic matrix. The coupling of void shape evolution with the plastic
anisotropy of the matrix leads to improved predictions for the yield surface
as well as the evolution of microstructural variables. An alternative numerical
approach is also developed to derive rigorous upper-bounds to the
yield loci for anisotropic porous materials of a given microstructure. Under
conditions of transverse isotropy, i.e. spheroidal voids in a transversely
isotropic matrix, and axisymmetric loading, the numerical approach delivers
quasi-exact results. Comparison of the analytical and numerical yield
loci for selected material properties indicates significant improvements with
respect to previous models from the literature.