Fretting fatigue of interference fitted joints: development of a novel specimen for four-point rotating-bending tests and experimental results

Interference-fitted joints are widely used to join a shaft and a hub. The contact pressure produced by the interference induces stress concentration on the shaft at the hub end. FEA can be helpful in evaluating the related stress concentration factor. However, fretting damage may be generated and may arise from micro-sliding between the mating surfaces. It is currently not feasible to take this occurrence into account and to properly and reliably address this phenomenon by a standard numerical simulation. In order to tackle this question, an ad hoc specimen was designed for four-point rotating bending fatigue testing. The new specimen has three main advantages: the first one is the reduced dimensions with respect to the usually tested shafts, the second is the possibility of controlling the average contact pressure, and the third is the capability of easily dismounting the specimen without damaging the coupled surfaces. The specimen has been then tested. The study focused on C40 normalized steel, whose fretting fatigue limit was experimentally evaluated by the aforementioned device. The mating surfaces could also be carefully analyzed for fretting damage detection after cycling. The fatigue limit retrieved was 254 MPa and fretting damage and induced cracks were detected in the specimens, which proves the effectiveness of the introduced testing rig at reproducing fretting fatigue damage.