Fatigue Performance of Repaired Aluminum Panels

Fatigue lives of some pre-cracked 7075-T6 aluminum panels that had been repaired using four different repair techniques have been investigated. The panels were repaired by patching over the cracks either with aluminum plates using rivets or with car bon/epoxy composite patches using adhesive. The same repair techniques, together with a 2 mm diameter hole drilled at the tip of the pre-crack, were also studied to evaluate the effectiveness of blunting the crack with such "stop holes." In comparison to the virgin panels, fatigue crack growth rates of the repaired panels were found to have decreased, with composite patches resulting in longer fatigue lives than the riveted patches. The intro duction of "stop holes" was observed to further retard the growth of the crack where an in crease in fatigue life of the repaired panels by some 50% was possible. No crack retarda tion was evident from panels repaired without the "stop holes."