Fatigue Response of Thin Stiffened Aluminum Cracked Panels Repaired with Bonded Composite Patches

This research investigated the fatigue response of precracked and patched 2024-T3 Aluminum panels with stiffeners. Patches were single-sided, unidirectional three ply boron/epoxy. Stiffeners were 2024-T3 aluminum and were riveted and bonded on. Disbonds were introduced into the repair bondline by inserting teflon strips. Three disbond configurations were investigated rack tip disbond (CTD) located at the edge of the patch in the path of crack propagation, full-width disbond (FWD) covering the entire crack, and end disbond (ED) located at each end of the patch and covering the full width. Each repaired panel was subjected to tension/tension cyclic fatigue with a maximum stress of 120 MPa. The effects disbonds had on fatigue life was studied by comparing disbonded repair fatigue life with that of perfectly bonded repairs. Results showed that disbonds closer to the crack that took up more bondline area had a larger negative impact on fatigue life. While disbonds did have some detrimental effects on repaired panel fatigue life, the disbonded repair cases still performed considerably better than an unrepaired panel. Results also showed that intentional disbonds did not experience significant growth during cyclic fatigue, and cyclic disbonding around the crack only occurred in the wake of the crack tip