Tribological Characteristics of Metallic Counterparts under Ultrasonic Elliptical Vibration

Wear behavior is influential to improve friction drive and wear lifespan of actuators or motors, which
work at ultrasonic elliptical vibration. Especially, the efficient friction-drive and durable wear-life are
critical for service performances of ultrasonic motors, particularly for standing-wave ultrasonic motors,
where the drive tip on the slider is in intermittent contact followed by impact effects. To investigate
wear mechanisms of metallic driving and driven parts, sliding wear tests of metallic friction pairs are
conducted by a laboratory rig of ultrasonic vibration. Surfaces of the different metallic sliders are
characterized by using surface roughness, Abbott curves and fractal dimension. Results show that
surface roughness is reduced to varying degrees in the metallic sliders due to ultrasonic polishing
and/or micro-rolling effect. Variations in the fractal dimensions of contact surfaces are consistent with
that of surface roughness. Wear traces demonstrate that plastic deformation and cracking are the
primary failure modes. Where the driving tip on the slider is in intermittent contact followed by impact
effects, ripples of 3~5 μm traces suggest the occurrence of fretting in duralumin sliders. Nodular cast
iron showed a favorable performance during running of ultrasonic motor, exhibiting a stable output
performance and durable wear life.