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Fretting fatigue mechanism of rapidly solidified powder aluminum alloy has been studied by model tests and analysis using fracture mechanics. The factors which influences upon fretting scar formation and fatigue crack propagation were the main concerns in the present work. In order to investigate the mechanism of fretting scar formation in detail, fretting wear tests in which small amplitude oscillatory movement occurred in the contact region were carried out. Test results showed that the size of fretting scar increased with increasing tangential force coefficient. Characteristics of fretting fatigue crack propagation were analyzed using fracture mechanics. The fatigue limits under fretting conditions were estimated by connecting the applied stress intensity factor range calculated from applied cyclic stress and tangential force, with the threshold stress intensity factor range of small crack.

A resonance type gear fatigue tester has been developed for fast and efficient evaluation of tooth-root fatigue strength. This tester is a sort of pulsating-type, and operates under quasi-resonance condition. One test gear is held stationary, and the mating gear fastened to a vibratory shaft oscillates against the stationary gear. The torsional vibration of the shaft is excited by a rotating eccentric. The torque amplitude is controlled automatically by varying the rotational speed of the eccentric and is maintained during a test. Fatigue tests and measurements of tooth-root strain were conducted on three kinds of helical gears, whose results were compared with those of a running-type fatigue tester. The results indicated that the tooth-root fatigue strengths with the resonance-type tester agreed with the running-type tester by taking the compressive strain which occurred at the tooth-root on the tension side in meshing, the dynamic load and the supporting rigidity in to account.