A new strain based damage model for structural concrete

Microcracking and plastic flow are the two physically distinct irreversible processes commonly found in brittle materials, like concrete. Plastic flow is a process in which particle dislocation and relocation takes place along the preferred slip planes. The effect of plastic flow is the development of irrecoverable strains in the material without altering the elastic properties. On the other hand, the development of microcracks and microvoids weakens the material bonds and alters the elastic properties. This microfracturing process results in the development of anisotropic elastic and inelastic damages. Both plastic flow and microcracking are to be addressed equally while developing a constitutive model for concrete.;A new strain based damage model for structural concrete is developed within the general framework of the internal variable theory of thermodynamics. It is assumed that a continuum approach can be taken to describe the constitutive relation for concrete and that coupled stresses are absent. For rate-independent behavior and infinitesimal deformations and utilizing the Helmholtz Free Energy (HFE) as an energy potential, a damage surface in the strain space is developed. Adopting additive decomposition of the stiffness tensor, kinetic relations are developed and used to capture the anisotropy caused by induced cracking. A damage function that is sometimes referred to as "critical strain" is identified in this work. The new damage model is checked against experimental data for uniaxial and biaxial stress paths both in tension and in compression.;To address plastic flow and damage, a single-flow surface model, in strain space, is developed utilizing the internal variable theory of thermodynamics. Scalar functions generated from volumetric strains are used in the dissipation inequality to generate a single-flow surface. This single-flow surface model is particularly tested for concrete through the formulation of specific response tensors, volumetric strain functions and damage functions. Finally, the model's ability to predict the enhancement in apparent ductility and strength in triaxial compression is compared against experimental results.