A PROGRESSIVE DAMAGE APPROACH FOR COMPOSITE STRUCTURES UNDER FATIGUE LOADING CONDITIONS

In this paper a fatigue damage propagation numerical model based on gradual material degradation rules and Hashin fatigue failure criteria is formulated, implemented in a finite element platform and then used to simulate the intra-laminar fatigue damage evolution in composite structures. The model has been preliminary validated against literature experimental data in terms of s-n curves providing confirmation of its effectiveness in predicting pinned composite joints fatigue life. The simulation of the models fatigue life provided detailed information on the intra-laminar damage mechanisms on-set and evolution related to fatigue gradual degradation of material stiffness and strength for different values of the applied maximum stresses. Finally an application to a delaminated stiffened composite panel, loaded in compression-compression fatigue, is presented. The intra-laminar damage propagation in the delaminated area and in the rest of the panel has been simulated considering the material properties gradual degradation with the fatigue cycles and the sudden failure arising according to fatigue stress based criteria