FRETTING FATIGUE OF A 2-1/2-PERCENT NICRMOV LOW-PRESSURE TURBINE SHAFT STEEL - THE EFFECT OF DIFFERENT CONTACT PAD MATERIALS AND OF VARIABLE SLIP AMPLITUDE

The fretting fatigue strength of a 2 1 2% NiCrMoV low pressure turbine shaft steel has been measured when in contact with fretting pads machined from En3, 3%CrMoV, 8%Mn8%Ni4%Cr and 2 1 2%NiCrMoV steels of different hardnesses. The fatigue strength reduction factors at a mean stress of zero were all in the range 2.6 to 3.2. Fractographic and metallographic studies of both fatigue specimens and contact pads revealed major differences in the type and extent of surface damage between the various material combinations. Fretting fatigue failures occurred over a wide range of relative slip amplitude with a minimum in fatigue life at a slip of approximately 25 μm. The experimental observations indicate that the initiation and growth of fretting fatigue cracks are controlled by the surface cyclic tangential stress which is a combination of the cyclic frictional stress induced by fretting and the bulk alternating stress. © 1990.