Damage in concrete: the unilateral phenomenon

Because the damage in a solid results from microscopic movements, we decided to include the power of these microscopic movements in the power of the internal forces. The microscopic velocities are related to the damage rate. The power of the internal forces that we choose depends on the damage velocity and its gradient to take into account the interactions. Models from this theory are presented. They are coherent from the mechanical and mathematical points of view. The numerical computations show no mesh sensitivity. They describe with good agreement the main experimental properties. Concrete is chosen as an example to illustrate the theory. A model using two damage quantities is also presented. It gives a description of the unilateral phenomenon observed in concrete. (orig.)