Effect of a Notch on the Fatigue Strength of a Gear Shaft

A failure of a gear shaft in an industrial application led to this investigation. The fractographic analysis revealed that the shaft was subjected to a high stress gradient at the failed location. Finite Element Analysis revealed that the nominal stress was way below the endurance limit of the material, however, due to the design of the shaft, a stress relief groove was used at a point where the shaft diameter had an abrupt change. The relief groove was necessary to properly fit the bearing on the shaft. The stress relief groove acted as a stress riser at the location. This was further verified by an experimental investigation of the stress gradient when in operation, optical imaging of the failed section and further a numerical analysis. A fracture mechanics analysis was used to assess the fatigue life of the notched component.