A cohesive interface model with degrading friction coefficient

A new model for cohesive interfaces is presented, based on energy and dissipation functionals and directly derived from thermodynamic principles, so that it is compatible with a continuum damage mechanics constitutive model for the continuum. Degradation of the interface is introduced through the dependency of the activation function on a driving force, dual to the internal variable of damage. The activation function of the interface is thus defined in the extended space of the tractions and of the conjugated forces, making it possible to model opening and reclosing, eventually with permanent residual relative displacements. An original feature of the model is that the friction angle degrades with the damage, modeling the reduction of the surface asperities, so that dilatancy tends to disappear. The evolution of the interface relative displacements is obtained from the conjugated dissipation functional, that is ruled by an associated flow rule.