A modified Ehlers model for inelastic behavior of foam structures

This paper describes a modification of Ehlers' model for the inelastic behavior of geomaterials. The newly developed modified model is intended to describe the inelastic behavior of highly porous media such as opencell foams. The key feature is a subtle change of the yield potential, which allows the correct orientation of the triangularly-shaped yield surface cross sections that depend on the hydrostatic stress state. The model is incorporated into a general framework for isotropic plasticity. An elastic predictor/plastic corrector algorithm is employed to solve the constitutive equations. The necessary analytical 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 Weaire-Phelan foam. The modified model provides an almost perfect prediction of the yield potential of the generic foam structure. The suggested modeling approach therefore shows great promise for its applicability to a wide range of isotropic porous structures.