Bifurcation investigations of coupled damage-plasticity models for concrete materials

This communication addresses the localization properties of a coupled damage-plasticity formulation for concrete materials to provide information on the onset of material bifurcation and the critical failure modes. Two separate loading functions are considered, one for damage and one for plasticity. A three-invariant yield surface is used to model plasticity and to consider the significant role of the intermediate principal stress and the Lode parameter on the failure of concrete materials. A non-associated flow rule is employed to control inelastic dilatancy. To model degradation of the elastic stiffness a scalar-valued isotropic damage formulation is introduced based on the total strain energy formulation that is used. Monotonic and cyclic uniaxial compression experiments are performed on concrete cylinders under displacement control and photogrammetric images are collected for Digital Image Correlation Analysis. The triaxial based damage-plasticity model is calibrated based on these experimental observations and is implemented in Matlab. Extensive localization analysis studies are performed at the constitutive level for representative load scenarios in the form of non-positive properties of the elastoplastic-damage localization tensor. The contributions of damage, plasticity and coupled damage-plasticity are explored and compared for classical Boltzmann and Micropolar Cosserat continuum formulations.