Failure Investigation of Counterweight Separation from Aircraft Propeller

Bokwon Lee, Ryan L. Karkkainen, Young Ha Hwang

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish (US)
Pages (from-to)568-579
Number of pages12
JournalJournal of Failure Analysis and Prevention
Issue number3
StatePublished - Jun 1 2018


  • Bolt failure
  • Counterweight
  • Thread stripping
  • Turboprop engine
  • XFEM

ASJC Scopus subject areas

  • Materials Science(all)
  • Safety, Risk, Reliability and Quality
  • Mechanics of Materials
  • Mechanical Engineering


Dive into the research topics of 'Failure Investigation of Counterweight Separation from Aircraft Propeller'. Together they form a unique fingerprint.

Cite this