Failure Investigation of Counterweight Separation from Aircraft Propeller
- 97 Downloads
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.
KeywordsBolt 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.
- 1.NTSB Identification, NYC98IA106 (1998)Google Scholar
- 2.M.M. Martinez, D.Z. Rios, An empirical model to calculate the threads stripping of a bolt installed in a tapped part. Eng. Technol. 46, 418–421 (2008)Google Scholar
- 3.M.M. Martinez, A. Ferrand, J. Guillot, Finite element analysis of thread stripping of a threaded assembly. Trans. Eng. Sci. 32, 263–272 (2001)Google Scholar
- 4.ASME B1.1, Unified inch screw threads, An American National Standards (American Society of Mechanical Engineers, New York, 1992)Google Scholar
- 5.R.T. Barret, Fastener design manual (NASA Reference Publication 1228, 1990)Google Scholar
- 6.ABAQUS Analysis User’s Manual 6.11, USA (2011)Google Scholar
- 7.MMPDS-1, Metallic materials properties development and standardization, 2nd Edition, September 2005Google Scholar