  This paper describes a modification of Ehlers' model for the inelastic
behavior of granular media. The modified model can be applied for describing
the inelastic behavior of porous media. The key feature is a subtle change of
the yield potential, which allows the correct orientation of the
triangular-shaped yield surface cross sections depending on the hydrostatic
stress state. The model is incorporated into a general framework for isotropic
plasticity. An elastic predictor/corrector algorithm is employed to solve the
constitutive equations. The necessary derivatives for a Newton update are also
given in detail. The model is calibrated using stress, and strain data obtained
from finite element simulations of a generic highly porous open-cell
Wheire-Phelan foam.
