Damage Concept and Its Applicability to Concrete

Damage to a material or structure expresses the gradual or sudden deterioration of the medium that forms them. This chapter presents the framework of the thermodynamics of irreversible processes, which is based on two major principles, one relating to the conservation of energy and the other to the production of entropy. Prior to the prediction of the fatigue failure of metal structures, tests are carried out on specimens to which sinusoidal loads are applied. At a given instant, the state of a material is described by state variables, which are classified into two categories: observable state variables and the internal state variables. The Helmotz free energy is a state function whose variation makes it possible to obtain the useful work likely to be provided by a closed thermodynamic system. The damage variable is also a state variable because it is associated with the state of the material at a given time.