Journal of Failure Analysis and Prevention

, Volume 18, Issue 3, pp 568–579 | Cite as

Failure Investigation of Counterweight Separation from Aircraft Propeller

  • Bokwon Lee
  • Ryan L. Karkkainen
  • Young-Ha Hwang
Technical Article---Peer-Reviewed


The counterweight of a propeller in a turboprop aircraft was separated during an engine run-up inspection. If this separation occurs in-flight, it may result in an accident involving serious damage or injury. In this investigation, the failed counterweight clamping assembly was studied to determine the root cause of failure. Both experimental and computational investigations were performed to explore and confirm the effects of experimentally observed anomalies on potential clamping assembly failure. Dimensional measurement of the failed clamping thread area by X-ray CT scanning revealed significant deviation from requirements in the major diameter of the thread. Fractographic and microscopic examination along with chemical analysis confirmed that the clamping bolts were pulled out due to overload stripping failure of the internal threads. Detailed computational fracture modeling utilizing the XFEM crack simulation technique provided further insight proving that thread engagement length had a significant effect on the clamping assembly failure. Based on these observations, it was concluded that the main root cause of the stripping failure was the dimensional nonconformance of the internal thread from the requirements in standard 7/16-20UNF-3B that resulted in the loss of thread engagement length.


Bolt failure Turboprop engine Thread stripping Counterweight XFEM 



The author would like to acknowledge the assistance of all the staff members of the failure analysis laboratory in ATRI at various stages in this investigation.


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Copyright information

© ASM International 2018

Authors and Affiliations

  • Bokwon Lee
    • 1
  • Ryan L. Karkkainen
    • 2
  • Young-Ha Hwang
    • 3
  1. 1.ATRI (Aero Technology Research Institute)DaeguRepublic of Korea
  2. 2.Department of Mechanical and Aerospace EngineeringUniversity of MiamiCoral GablesUSA
  3. 3.Korea Institute of Industrial TechnologyYeongcheon-siRepublic of Korea

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