Aluminum 7075 stress-corrosion cracking in aircraft structures

Generic mechanism behind the Brazilian rotor spar failure; mentioned without alloy specified, but the high-strength aluminum + paint-protection failure pattern matches the 7075 cluster.

I went back and looked at photos. I said, metallurgically, on the surface, it was stress corrosion cracking. The problem was not that they had sanded the surface — they hadn't repainted it well enough to protect it from stress corrosion cracking of a high-strength aluminum. They got a stress corrosion crack which was a three-millimeter-deep crack, which now fracture mechanics could explain. I gave my deposition. The plaintiffs were very unhappy, because the helicopter company had come out with an alert service bulletin saying you've got to be careful and inspect all this stuff. After I gave my deposition, the helicopter company went back, had their engineers look at what I had said, redid the calculations, and withdrew their service bulletins, because they got it wrong. People just say, oh, I had a scratch, and a scratch caused the whole thing to fail. Well, scratches don't cause a ductile metal to fail. They might cause a piece of glass to fail, but they don't cause a piece of metal to fail. And I see two people a year in some failure claiming that — oh, the scratches caused the failure. Not in metals, folks.