Failure investigation of pure titanium bleed air ducts in jet fighters

Bokwon Lee, Garrett Nygren, Ryan L. Karkkainen, Jinyi Lee

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


This paper describes the failure investigation of in-flight failures of bleed air ducts in jet fighters. Severe rupture had occurred at the bleed air duct during the flight that had caused the emergency landing situation. The tubular duct was manufactured using commercially pure titanium. An inspection revealed that all cracks occurred in the central portion of the bleed air duct. Examination of the fractured surfaces by using electron microscopy revealed that cracks initiated at multiple corrosion pits in the inner surface of the duct and these propagated by brittle cleavage cracking with occasional areas of fatigue striations induced by in-service cyclic pressure. Fractography, chemical analysis, and metallographic analysis confirmed that brittle fracture involved the ingress of hydrogen into a duct surface. The hydrogen effectively decreased the ductility of the duct which contributed to brittle fracture. The final destructive rupture of the duct can be explained by fracture mechanics. The critical crack size and stress induced by conditions at or near the operating load were estimated based on computational fracture analysis to explore the fracture mechanism. As a consequence, a novel nondestructive inspection method has been developed to prevent such failures in future.

Original languageEnglish (US)
Pages (from-to)381-392
Number of pages12
JournalEngineering Fracture Mechanics
StatePublished - Feb 1 2018


  • Aircraft
  • Corrosion pits
  • Environmentally assisted cracking
  • Extended finite element method
  • Failure analysis
  • Titanium duct

ASJC Scopus subject areas

  • Materials Science(all)
  • Mechanics of Materials
  • Mechanical Engineering


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