Small-amplitude cyclic sliding motion at the interface between two solid bodies pressed together by a normal force initiates microcracks which propagate and cause premature fatigue failure. This action is defined to be fretting-fatigue. A quantitative evaluation of fretting-fatigue damage would be of great value to the mechanical engineering designer. It is proposed that a fretting-fatigue damage-factor could be developed to provide a quantitative index to fretting-fatigue damage. The damage-factor proposed is a function of eight basic fretting-fatigue parameters. Experimental tests were conducted to establish quantitative values for the fretting-fatigue damage-factor for a few specific sets of fretting-fatigue conditions. An unexpected trend in the value of the fretting-fatigue damage-factor was observed for the case of static stress in the specimen during fretting. With a static tensile stress in the specimen during fretting, the fretting-fatigue damage, as measured by reduction in fatigue limit, was very slight, while with a static compressive stress in the specimen during fretting, the fretting-fatigue damage was very great. A tentative explanation is presented.

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