FRETTING FATIGUE STRENGTH OF SEVERAL MATERIALS COMBINATIONS.

Fretting fatigue tests are carried out with various materials combinations, and the reduction rates of fatigue strength by fretting are obtained with an observation on the behaviors of frictional force. Stress analyses on the contacting surfaces are conducted elastically by using the maximum stress due to friction together with repeated stress applied on specimens, and the results are compared with the experimental results. The fatigue strength is reduced more remarkably by fretting under bending than under twisting and the damage is greater to materials combination with higher tangential stress. These results agree fairly well with the consideration where the fatigue cracks are initiated under the maximum repeated shearing stress calculated from the combination of bending or twisting stress and frictional stress. The strength reduction rate is, however, greater than the analytical one for specimens of aluminum alloy and for lower cycle frequencies. Although further studies should be made on the behaviors in fretting fatigue which are similar to those in corrosion fatigue, it may be concluded that the initiation of fretting fatigue cracks is due to the maximum repeated shearing stress.