  A finite-strain formulation is developed, implemented and tested for a
constitutive model capable of describing the transition from granular to fully
dense state during cold forming of ceramic powder. This constitutive model (as
well as many others employed for geomaterials) embodies a number of features,
such as pressure-sensitive yielding, complex hardening rules and elastoplastic
coupling, posing considerable problems in a finite-strain formulation and
numerical implementation. A number of strategies are proposed to overcome the
related problems, in particular, a neo-Hookean type of modification to the
elastic potential and the adoption of the second Piola-Kirchhoff stress
referred to the intermediate configuration to describe yielding. An incremental
scheme compatible with the formulation for elastoplastic coupling at finite
strain is also developed, and the corresponding constitutive update problem is
solved by applying a return mapping algorithm.
