Mixed-mode delamination with large displacement modeling of fiber-bridging

Crack bridging mechanisms, such as fiber-bridging and fibrillation, take place in many different types of interfaces upon the development of large relative displacements between the separating faces. Cohesive models that do not account for these mechanisms inevitably underestimate the interface strength. On the other hand, consideration of large interface openings implies tackling a number of mechanical and geometrical difficulties, conflicting with the basic assumptions behind the cohesive model. A simple strategy to deal with large openings and fiber-bridging in cohesive models is discussed in the present contribution. A recently proposed cohesive model for mixed-mode delamination is used to model the interface behavior until the normal opening remains small, while the remaining cohesive energy is transferred to a co-linear fibril element when a critical opening threshold is reached. The initial use of a mixed-mode cohesive model allows to correctly define the complex evolution of the fracture energy with the mode-ratio in the initial, short range phase of the cohesive resistance, while the fibril correctly models the interface behavior in the final, long range phase, where crack bridging mechanisms are dominant. Some preliminary numerical examples confirm the accuracy and robustness of the proposed procedure.