• Cohesive Elements
• Composites Delamination
• Damage Propagation
• Fatigue Delamination
• Fatigue in Composites
• Fatigue Propagation

The present thesis aims at developing a cohesive element behaviour for predictive analysis involving delamination in composites under cyclic loading. The key feature of the proposed method is the implementation of a degradation law that slowly decrease the cohesive properties of the element itself with the number of elapsed cycles. In this way, damage can be accumulated, and a crack can grow, also when local stress is lower than the cohesive strength of the element, that is the typical situation of fatigue problems. The formulation is capable of an automatic identification of the initiation zone, and can reproduce propagation of a crack as well. Several algorithms are developed, starting from a simple one to finally obtain a satisfying degradation law. Simulations are performed under various mode-mixity conditions using Double Cantilever Beam, End Notched Flexure and Mixed Mode Bending tests, as well as a more complex laminated structure. Finally, simulations performed to compare the model with experimental data proved quite satisfying.