The main goal of this thesis is the simulation of the performance of composite naval structures subjected to cyclic loads. The predicted behavior expected is the fatigue life of the composite structure, as well as the fatigue failure mechanisms. This achievement is conducted by coupling the serial/parallel mixing theory and a fatigue damage model. Consequently, the work has the following stages. In first place, a study is conducted in order to identify the failure mechanisms of composites in fatigue and how the different factors affect it, in order to propose a fatigue constitutive model for fibre and matrix. The review uses a constituent materials point of view, thus fatigue performance of fibres and resins are analyzed, as well as their role in each failure mechanisms. In addition, different variables that may affect fatigue behavior are described. Secondly, a numerical procedure for characterizing fibres and matrix is proposed, in order to predict the failure mechanisms in composites subjected to static loads. The procedure defines which experimental tests should be conducted and what material parameters are obtained from them. As a consequence, the material parameters of the constituent materials are defined, obtaining the failure of the composite by the failure of the constituent materials, without pre-defining the expected failure. The next stage is coupling the serial/parallel mixing theory and the fatigue model. The fatigue model modifies the constitutive equation of the components, while the rule of mixtures acts as a constitutive law manager. The fatigue models of fibre and matrix are characterized, assuming that the fatigue behavior of unidirectional laminates is driven by one of the constituents, in function of the loading direction. This methodology is validated for two different composite systems: a carbon epoxy cross-ply laminate and glass/polyester balanced angle-ply laminates. Finally, this numerical methodology is applied to two naval structures: a small section of a container ship and a flexible composite blade of a marine propeller. The two analyses obtain the failure mechanisms of both structures, as well as the ply or plies failing, and the corresponding constituent material causing the failure. One of the fatigue analyses is used in order to propose a simplified method capable of predicting the fatigue initiation in the structure, by only applying a quasi-static analysis. This method is based on comparing the maximum equivalent stress in the components with their SN fatigue curve.