Effect of the contact conditions and surface treatments on the fretting fatigue strength of medium carbon steel

Fretting fatigue tests characterized with employing a contact bridge pad clamped to a fatigue specimen were conducted to find the effect of shapes of contact pads. The shapes of the contact edge of the pad used in the test were sharp and round. The relative slip amplitude during fatigue testing was measured and the effect of the location of the displacement sensor was discussed with the result of the stress analysis around the contact area. The effect of molybdenum coating on the fretting fatigue strength was also investigated. It was found that by using the round edge pad, reproducible fretting scars could be obtained and also the round edge pad prevented the fatigue failure at the contact edge. A remarkable difference of the measured slip amplitude was found by the location of the displacement sensor. The molybdenum coating increases the fretting fatigue limit about 1.5 times that of the fretting fatigue strength of uncoated specimens. Fretting fatigue cracks always initiate at the inner site of the contact area. The results were explained from the results of contact stress analysis where the maximum shear stress occurred at the inner surface of the contact area in both types of the pad.