Forensic Engineering Investigation of a High-Voltage Transmission Line Anchor Shackle Failure




high voltage transmission line, shackle hardware, Charpy tensile test, low-temperature fracture toughness, experimental design, statistical sample, forensic engineering


A forged alloy steel anchor shackle, one of a batch of more than 2,600 produced for the project, failed catastrophically in service on a newly erected 66-kilometer high-voltage transmission line in northern Canada. A failure analysis led to a hypothesis that forging laps had created the critical crack size to initiate propaga-tion under cold weather conditions. An extensive Charpy fracture toughness test program based on CAN/CSA C83.115-96 parameters was performed on 150 shackles, but the data did not support the initial hypothesis of temperature dependence. The forensic engineering team designed experimental tensile tests at ambient tem-peratures as low as -40°C to evaluate the propagation response of lap cracks in a statistically valid sampling of shackles. The trimmed forging flash area disguised laps from the manufacturing process, and subsequent galvanizing steps prevented detection by magnetic particle inspection. A focused recommendation for removal and replacement of the shackles was issued for those bearing major loads in the tower array.


For more information on applied quality theory in manufacturing practice, visit American Society for Quality at, and see

Communication and Power Line Hardware, CAN/CSA C83-96 (2011), Canadian Standards Association, Etobicoke, ON, Canada, 2011.

Communication and Power Line Hardware: Appendix J, CAN/CSA 83.115-96 Shackles, Canadian Standards Association, Etobicoke, ON, Canada, 2011.

Standard Test Methods and Definitions for Mechanical Testing of Steel Products, ASTM A370-19e1, ASTM, West Conshohocken, PA, USA, 2019.

General Requirements for Rolled or Welded Structural Quality Steel, CAN/CSA G40.20, Canadian Standards Association, Etobicoke, ON, Canada, 1998.

Standard Test Methods for Notched Bar Impact Testing of Metallic Materials, ASTM E23-12c, ASTM, West Conshohocken, PA, USA, 2012.

Richard W. Hertzberg, Deformation and Fracture Mechanics of Engineering Materials. Hoboken, NJ, USA: Wiley, 1976, pp 327-335.

William F. Hosford and Robert M. Caddell, Metal Forming: Mechanics and Metallurgy Second Edition. USA: Prentice Hall, 1993, pp 244-303.

George E. P. Box, J. Stuart Hunter and William G. Hunter, Statistics for Experimenters: Design, Innovation and Discovery. Hoboken, NJ, USA: Wiley, 2005.

Bert Gunter and Daniel Coleman., A DOE Handbook: A Simple Approach to Basic Statistical Design of Experiments. USA: CreateSpace, 2014.




How to Cite

Couture, Daniel P. 2022. “Forensic Engineering Investigation of a High-Voltage Transmission Line Anchor Shackle Failure”. Journal of the National Academy of Forensic Engineers 39 (1):35-46.