A cardon shaft operating in an aircraft engine failed and was taken out and analyzed to determine the cause. A photograph of the broken shaft in the as-received condition shows the location and orientation of the fracture. The fracture surface appeared smooth, indicating that a considerable amount of rubbing occurred after the shaft broke. SEM fractography revealed deformation marks and elongated dimples, typical of shear overloads, along with other details. Based on their analysis, investigators concluded that the cardan shaft failed under torsional overload. They also cited a need for a more detailed examination of the driven end of...