Torsional Failures in Hollow Axle Shafts from an F1000 Race Car

We investigated the failures of two hollow axle shafts from an F1000 race car. This race car is powered by a Suzuki GSXR1000 motorcycle engine that uses a chain drive to spin the rear differential that the axle shafts connect to. One axle shaft failed while racing in the SCCA Sprints at Road America in 2021 and the other during testing at Circuit of the Americas in October 2020. Notably, both axles failed in a similar manner and the direct cause of the failure was torsional fatigue. The metallurgical investigation revealed that pre-existing flaws on the inner surface along the length of hollow axle shaft initiated the fatigue cracks. Prior to these failures, similar hollow axle shafts from the same vendor were used without issue; this led to an investigation into possible changes in the manufacturing process. Recommendations were made to mitigate the stress concentrations that initiated fatigue cracking in these axle shafts.