Forming limit during superplastic deformation of sheet metals
A thermo-viscoplastic damage potential and Hill's normal anisotropy (isotropy in plane) yield criterion, quadratic in the stress components, are combined to describe the interaction of damage and instability during superplastic deformation, based on the kinetic equation for damage. The superplastic deformation process is divided into four stages, namely stable, quasistable, strain path drift to plane strain, and plane strain stages.
Hill's normal anisotropy yield criterion
scientific article; zbMATH DE number 892223