Handbook of Case Histories in Failure Analysis
Processing-Induced Fatigue Fracture of a Helicopter Tail Rotor Blade
Formerly Head, Metallic Materials Engineering, Naval Aviation Depot, Pensacola, Florida
A helicopter tail rotor blade spar failed in fatigue, allowing the outer section of the blade to separate in flight. The 7075-T7351 aluminum alloy blade had fiberglass pockets. The blade spar was a hollow “D” shape, and corrosion pits were present on the inner surface of the hollow spar A single corrosion pit, 0.38 mm (0.015 in.) deep, led to a fatigue failure of the spar The failure initiated on the pylon side of the blade. Dimensional analysis of the spar near the failure revealed measurements within engineering drawing tolerances. Though corrosion pitting was present, there was an absence of significant amounts of corrosion product and all of the pits were filled with corrosion-preventative primer. This indicated that the pitting occurred during spar manufacture, prior to the application of the primer The pitting resulted from multiple nickel plating and defective plating removal by acid etching. Post-plating baking operations subsequently reduced the fatigue strength of the spar.
Richard H. McSwain, Processing-Induced Fatigue Fracture of a Helicopter Tail Rotor Blade, Handbook of Case Histories in Failure Analysis, Vol 2, Edited By Khlefa A. Esaklul, ASM International, 1993, p 33–35, https://doi.org/10.31399/asm.fach.v02.c9001298
Download citation file:
New Handbook: Volume 11B
Now available in the Digital Library! Volume 11B serves as a reference and guide to help engineers determine the causes of failure in plastic components and make corrective adjustments through design and manufacturing modifications.