Failure Investigation of an F1000 Racecar Wheel Center

We investigated the root cause of an F1000 racecar wheel failure and provided recommendations for potential corrective actions. Through thickness cracks were discovered in three of the spokes after several races, during which there were no reported crashes or notable incidents. Dye penetrant testing revealed additional cracks of varying size on all spokes in the same location as the through-thickness cracks. We evaluated the stresses in the wheel spokes during dynamic cornering using finite element analysis (FEA), which identified the failure region as a stress concentration under a cyclic reversed bending load. Observed machining marks in the failure region further concentrated the stress. The fracture surface revealed features consistent with fatigue, such as potential beach marks and ratchet marks. Additionally, cantilever curl was identified at the termination of fracture, which is consistent with a bending load. ThermoCalc® equilibrium phase modeling of the measured alloy composition indicated that Mg2Si precipitates are stable past the solidus temperature, suggesting possible challenges with breaking down the eutectic component of the solidification structure. Metallography showed an anisotropic structure with elongated bands of high precipitate density, consistent with the prediction of an intact eutectic component. A crack was revealed propagating through the eutectic component parallel to the banding direction, suggesting an interaction between the two. We concluded that the wheel center failed by high cycle fatigue primarily due to the stress concentration at the fillet on the interior face of the wheel center and exacerbated by microstructural anisotropy. We provided recommendations related to improved manufacturing processes to reduce stress concentration and heterogeneous microstructural constituents, as well as considerations for material selection.