Metallurgical failure analysis was requested after a company experienced several identical shaft failures. Macro and microscopic examination revealed that these shaft failures were the result of bending fatigue. The metal fatigue, which was observed on the shaft fracture surface, was due to an inadequate filet radius at a diameter change in the subject shaft. The inadequate radius was due to a machining error and was a manufacturing defect.
Photograph A Failed shaft, which separated at a diameter transition.
Photograph B Two halves of the failed shaft.