Forensic Deformation Analysis of a Farm Clevis Using Photographs and Exemplar Tests

Two ARCCA experts recently published ‘Forensic Deformation Analysis of a Farm Clevis Using Photographs and Exemplar Tests‘ in Vol. 42 No. 1 of the Journal of the National Academy of Forensic Engineers (NAFE). This team includes Michael Stichter, PhD, PE, DFE, (NAFE 1162M) and Wade Lanning, PhD of ARCCA’s Failure Analysis engineering group.

This publication reviews a case where a failed component (a farm clevis or round pin shackle) was part of equipment used to attempt to recover a vehicle mired in the mud at an above-ground mine site. The shackle failed, and the shackle pin became a projectile that penetrated the cab and injured the driver. The subject clevis was not available for physical inspection or testing. However, the condition of the subject clevis after the accident had been documented in photographs.

Application of solid mechanics principles made it possible to determine the sequence of deformation steps that occurred during the failure. Additionally, comparing the deformation behavior documented in photographs of the subject clevis — and to tests of exemplars — allowed a determination of the strength of the subject clevis. Thus, investigators were able to use photographs to determine that the clevis’ shackle failed due to longitudinal tensile forces in excess of its working load limit (WLL) and elastic limit. Since the failure occurred above the WLL of the component, the shackle failed due to excessive loads, not a defect.

For more details on this publication, visit NAFE here to download and view a copy of the paper.