Combined damage and plasticity approach for modeling brittle materials with application to concrete

Microcracking and inelastic flow are two physically distinct irreversible processes commonly found in brittle materials like concrete. The inelastic flow is characterized by a process, in which particle dislocation and relocation takes place along the preferred slip planes leading to the development of irrecoverable strains in the material without altering elastic properties. On the other hand, the development of microcracks destroys material bonds and alters elastic properties leading to anisotropic damage. Microcracking and inelastic flow interact with each other in the presence of confining stresses. This paper presents a single-flow surface model for brittle solids unifying damage mechanics and plasticity. The necessity of using a singleflow surface model over the existing bi-surface model is discussed. The model is cast within the general framework of the internal variable theory of continuum thermodynamics, using strain space formulation, where an internal dissipation inequality is established. The model is particularly tested for concrete through the formulation of specific response tensors, volumetric strain functions and damage functions. The model is capable of capturing essential features of concrete inelasticity including anisotropic stiffness degradation, inelastic flow, and increase in apparent ductility and strength with lateral pressure, and is compared against experimental results.