Damage tolerance of adhesive bonded stiffened panels: experimental and analytical investigation of the fatigue crack propagation underneath the stringers

On the basis of well-known literature, an analytical model was developed by the authors to provide reliable predictions on the fatigue propagation of cracks growing through the skin underneath adhesively bonded stringers of aeronautical stiffened panel. In order to exploit the significant damage tolerance proprieties of adhesively bonded stiffened panels it is indeed fundamental to take into account the slow fatigue crack growth under the bonded stringers, currently completely neglected as a consequence of the limits of the employed prediction tools. The correlation between the model predictions and experimental fatigue crack propagation test results of wide stiffened panels permitted to validate the model and to provide a deep insight into the mechanisms involved during the skin crack propagation under the bonded stringers of fatigue loaded panels. The implemented model confirmed its reliability in describing the fatigue skin crack propagation under the bonded stringers, but phenomena that can occur during this propagation phase, as adhesive delamination that can develop around the advancing crack tip and the fatigue failure of the bonded stringer must be taken into account in order to obtain reliable predictions.