Ultrasonic lubrication has been proven effective in reducing dynamic friction. This paper investigates the relationship between friction reduction, power consumption, linear velocity, and normal stress. A modified pin-on-disc tribometer was adopted as the experimental set-up, and a Labview system was utilized for signal generation and data acquisition. Friction reduction was quantified for 0.21 to 5.31 W of electric power, 50 to 200 mm/s of linear velocity, and 23 to 70 MPa of normal stress. Friction reduction near 100% can be achieved under certain conditions. Lower linear velocity and higher electric power result in greater friction reduction, while normal stress has little effect on friction reduction. Contour plots of friction reduction, power consumption, linear velocity, and normal stress were created. An efficiency coefficient was proposed to calculate power requirements for a certain friction reduction or reduced friction for a given electric power.
This article presents an analytical model for piezoelectrically-assisted ultrasonic friction and wear reduction. A cube is employed to represent the asperities in contact between two surfaces. Dynamic friction is considered as the sum of two friction components that depend on deformation of the cube and relative velocity. Ultrasonic vibrations change the geometry, contact stiffness, and deformation of the cube, as well as the relative velocity, which leads to a reduction in the effective dynamic friction. Volume loss of surface wear is explained by the integral of half of the cube volume over the time duration of the sliding. Change of the cube geometry caused by ultrasonic vibrations results in a change of the cube volume. A piezoelectrically-assisted tribometer was designed and built for pin-on-disc friction and wear tests. The experimental measurements validate the model for ultrasonic friction reduction at various macroscopic sliding velocities, and for ultrasonic wear reduction at various sliding distances with most errors less than 10%.
It has been shown that the coefficient of dynamic friction between two surfaces decreases when ultrasonic vibra-
tions are superimposed on the macroscopic sliding velocity. Instead of longitudinal vibrations, this paper focuses
on the lateral contractions and expansions of an object in and around the half wavelength node region. This
lateral motion is due to the Poisson effect (ratio of lateral strain to longitudinal strain) present in all materials.
We numerically and experimentally investigate the Poisson-effect ultrasonic lubrication. A motor effect region
is identified in which the effective friction force becomes negative as the vibratory waves drive the motion of the
interface. Outside of the motor region, friction lubrication is observed with between 30% and 60% friction force
reduction. A "stick-slip" contact model associated with horn kinematics is presented for simulation and analysis
purposes. The model accurately matches the experiments for normal loads under 120 N.
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