A coupled elastoplastic damage model for geomaterials

Abstract

A triaxial constitutive model is developed for elastoplastic behavior of geomaterials, which accounts for tensile damage. The constitutive setting is formulated in the framework of continuum thermodynamics using internal variables. The interaction of elastic damage and plastic flow is examined with the help of very simple constitutive assumptions: (i) a Drucker–Prager yield function is used to define plastic loading of the material in combination with a non-associated flow rule to control inelastic dilatancy ; (ii) elastic damage is assumed to be isotropic and is represented by a single scalar variable that evolves under expansive volumetric strain. Thereby, positive volumetric deformations couple the dissipation mechanisms of elastic damage and plastic flow which introduce degradation of the elastic stiffness as well as softening of the strength. The constitutive model is implemented in the finite element program ADINA to determine the response behavior of the combined damage-plasticity model under displacement and mixed control. A number of load histories are examined to illustrate the performance of the material model in axial tension , compression, shear and confined compression. Thereby incipient failure is studied at the material level in the form of non-positive properties of the tangential material tensor of elastoplastic damage and the corresponding localization tensor comparing non-associative with associative plasticity formulations.